Archives: Surgery Techniques

Cataract Surgery

What is a cataract ?

The eye lens, consisting of fibers, can not only become less elastic with age (presbyopia) but also cloudy. A similar effect of “nuclear sclerosis” also occurs in cases with pets. Cataract disease is a kind of clouding of the vitreous body (the lens of the eye). In that case the cataract surgery is recommended.



The word cataract has been translated from Latin as a waterfall since ancient Roman times as the clouding of the lens was represented like the white foam of a waterfall 1. Although some cataracts can be congenital, caused by trauma, smoking, diseases (such as diabetes), and oxidizing drugs, age-related cataracts are considered the main ones 2. It is believed that cataracts cannot be avoided otherwise by eating and living the right way. Cataract disease may occur sooner or later. It’s just a matter of time.




The lens of the eye also acts as UV filter protecting the retina from its damage. Nutrients pass through the fibers of the lens and thus, the lens acts as an oxygen scavenger with a high concentration of antioxidants. Induced oxidative damage can accompany corneal opacity 2.




If the cataract is not “treated” (replaced eye lens) then the person can become permanently blind. The main cataract complications are increased eye pressure or glaucoma, inflammation of the choroid, but it can be seen at the initial level with the help of modern diagnostic equipment.




 


How is cataract surgery and lens replacement performed ?


For a long time over the centuries, the surgeon pushed an opaque lens into the vitreous cavity with a needle, thus clearing the way for the propagation of light in the eyeball. At the very least, such a method could restore hope to blind cataract patients with completely clouded lenses. Since more than 20 diopters of optical power are concentrated in the lens of the eye, appropriate glasses were required after such an operation.




Since the eighteenth century the development of implantation of artificial lenses for cataract disease (replacement of the lens) began. During World War II, it was observed1 that damage to the eyes of pilots by some materials resulted in minimal intraocular irritation. So attention was paid to this material but this did not help to avoid postoperative inflammation. Another problem was the dislocation of the lens in the eye lens capsule. There was still work to be done to improve the centering of the artificial lens when calculating the optical power of the IntraOcular Lens (IOL).




Depending on which part of the eye lens capsule becomes cloudy, that part is operated on (capsulotomy):




a) capsulotomy for cataract of the lens nucleus,




b) treatment of cataracts with clouding of the outer shell of the capsule,




c) capsulotomy of the clouded posterior lens shell.




In the first case the symptoms may be a deterioration in the clarity of vision at a distance and near. In others, it may be visual impairment in illuminated spaces.




Cataract Surgery IOL




Fig. 1. Schematic representation of the position of the IOL in the eyeball is indicated in yellow. Antennae are needed for a stable position in the capsule of the eye




FemtoSecond Laser and Phacoemulsification


The introduction of the femtosecond laser to the ophthalmic market has made it easier for surgeons to perform cataract surgery. With the help of the laser the accuracy and safety of the corneal incisions necessary for the removal of the lens, as well as for its fragmentation (fragmentation), were improved.




The native lens of the eye can also be fragmentized with an ultrasonic tip and sucked out (aspiration process) through the desired incision in the eye – phacoemulsification.




Such technologies have helped to avoid a long stay of patients in the hospital after cataract surgery.






Advantages of IOL implantation over laser correction for presbyopia


One of the biggest advantages of IOL implantation is that it can be removed if the IOL does not compensate for lost vision. The IOL can be removed from the eye and a new one put in without changing the thickness of the cornea, as would be required when correcting laser vision for presbyopia.






Future prospects of IOLs


It is known that IOL lenses can be of three types depending on the calculations and properties of the cornea (multifocal, monofocal and toric). An ideal IOL would be an accommodative IOL that could contract like the natural lens of the eye.




Attention! If you have more recent information, we will be happy to accept it. If you have any questions, put it on the forum (https://findsurgery.eu/forum/) or ask directly by email info@findsurgery.eu.


 


 


Bibliography


    

  1. Krueger RR, Talamo JH, Lindstrom RL. Textbook of Refractive Laser Assisted Cataract Surgery (ReLACS). (Krueger, Ronald R. Talamo, Jonathan,H. Lindstrom RL, ed.). Springer New York Heidelberg Dordrecht London; 2013. doi:10.1007/978-1-4614-1010-2
    2. 

  2. Moshirfar M, Milner D, Patel BC. Cataract Surgery. In: Treasure Island (FL); 2022.
    3. 


	


	

			






	

		
Corneal Implants for presbyopia, corneal segments and rings
	


	
	

		
In addition to laser vision correction and intraocular lens replacement, there are also various types of corneal implants and implantable collamer (also contact) lenses (ICL) 1 2 3.






What are corneal implants?


Methods where synthetic materials (implants) are inserted into the cornea to reshape it encompass IntraCorneal Lenses (ICL for presbyopia also known as inlays), Rings (ICR) and Ring Segments (ICRS) 4. Unlike Implantable Collamer (Contact) Lenses, also abbreviated as ICL, and Intraocular Lenses (IOL), which are implanted behind the cornea or in the back chamber of the eye, respectively, the implants are inserted into the incision made in the cornea. In case of refractive error between +4 diopters and -8 diopters Implantable Contact Lenses can be used, while the IOL is preferred for cataract. The Implantable collameral (contact) lenses (ICL) have advantages for the correction of myopia and myopic astigmatism due to their predictability, stable refraction, and high efficiency. Studies have shown a low incidence of unwanted symptoms 5. In the case of presbyopia, intracorneal rings or lenses may be used. In case of keratoconus corneal segments can be used for therapeutic purposes  2.






Types of corneal implants


For the treatment of presbyopia rings and lenses are implanted into the cornea.




The meaning of the corneal ring is that it improves near vision in the non-dominant eye, but retains distance vision with two eyes 6. That is such a ring restricts the flow of light into the eye and is a kind of a narrow pupil.




Presbyopic intracorneal lenses change the curvature of the cornea in the middle, but not change it in the periphery. This creates a multi-vocal effect similar to Presby-LASIK (see Presby-LASIK).




Other intracorneal lenses may have a hole in the middle for distance vision surrounded by a neutral optical zone and refractive power at the periphery of the lens for near vision 6.






Benefits of corneal implants


The main advantage of corneal implants is the reversibility of the operation, i.e. they can always be removed if the effect is unsatisfactory 1 6.




However, central corneal opacity may occur. In turn corneal rings restrict light from entering the eye, which can reduce the contrast and quality of night vision, and may also cause optical side effects.




Studies using intrastromal (stroma – the main part of the cornea) segments (ICRS) in keratoconus to correct astigmatism have shown improvement in visual acuity and refraction of the eyes in the first three years 2.






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Bibliography


    

  1. Alio JL. Management of Complications in Refractive Surgery. (Alió JL, Azar DT, eds.). Berlin, Heidelberg: Springer Berlin Heidelberg; 2018. doi:10.1007/978-3-540-37584-5
    2. 

  2. Min-Ji K, Yong-Soo B, Young-Sik Y, et al. Long-term outcome of intrastromal corneal ring segments in keratoconus: Five-year follow up. Sci Rep. 2019;9(1):1-7.
    3. 

  3. Higginbotham J. Correcting Presbyopia – Modern Options Head of Clinical Affairs What is Presbyopia ? Birmingham Opt. 2016:44. https://de.slideshare.net/JasonHigginbotham/correcting-presbyopia-modern-options.
    4. 

  4. Shortt AJ ABDS, Evans JR. Laser assisted in situ keratomileusis (LASIK) versus photorefractive keratectomy (PRK) for myopia. Cochrane Database Syst Rev. 2013;(1). doi:10.1002/14651858.CD005135.pub3
    5. 

  5. Packer M. Meta-analysis and review: effectiveness, safety, and central port design of the intraocular collamer lens. Clin Ophthalmol. 2016;10:1059-1077. doi:10.2147/OPTH.S111620
    6. 

  6. Arba Mosquera S, Alió JL. Presbyopic correction on the cornea. Eye Vis (London, England). 2014;1:5. doi:10.1186/s40662-014-0005-z
    7. 


	


	

			






	

		
Personalized laser vision correction
	


	
		

		
	

		
Often patients familiarizing themselves with the list of operations offered by a medical institution notice how the price tag differs from a common surgery type. This is especially true for the so-called personalized (individual or customized) methods, i.e. personalized laser eye surgery. The marketing term “Super” is often placed next to the type of a surgery. Why do clinics overcharge because of this “Super”? Let’s figure it out together. We want to make a reservation right away that not everyone does this. It looks like the price for the same type of surgery in different clinics may differ by a factor of two or more, although the same equipment is used. Conventional laser vision correction for the treatment of refractive errors accounts for the lion’s share of laser refractive corneal surgery. Nevertheless, there are about 10% of patients (we speak from our own experience) who need an individual approach.




Sometimes this approach is necessary in order to try to eliminate irregularities (see Fig. 1) and to achieve a better result or some kind of scars on the surface of the cornea for therapeutic purposes (scar eyes), irregular astigmatism (see Myopia, astigmatism and laser vision correction). Eye laser correction of presbyopia is often referred to individual methods as there an additional depth of field is achieved in the distance and for reading 1 2. Individual approach is also necessary to correct any consequences of unsuccessful operations. Such irregularities are called high-order aberrations. Low order aberrations include myopia, hyperopia, and astigmatism. Roughly speaking, an individual approach is needed in cases where high visual acuity cannot be achieved with glasses. In such cases, there are various effects like ghosting, glare or splitting at the edges of the image, etc.




Technique of personalized laser vision correction


Fig. 1. Schematic representation of irregularities






If you have a prescription for your glasses, then there are low order aberrations. One of the first will be recorded, for example myopia Sph. -2Dpt. with astigmatism in the form of the presented refractive cylinder Cyl. -1Dpt., Rotated by any degree (see Astigmatism). And as we know, this is temporarily corrected by a simple selection of glasses at the doctor’s office. In this case, the recipe for myopic astigmatism is Sph. -2 diopters / Cyl. -1Dpt. @ 180o.




Personalized laser ablation requires a thorough analysis of the topography of the eye, i.e. maps of corneal irregularities and its optical power in each area, each of which has an effect on the quality of vision. Such a measurement is made by a device called a topographer. Therefore, you cannot simply take and evaporate the same amount of tissue in nearby areas like in common optimized surgery types. It may not be enough to investigate how the cornea focuses light; additional scattering comes from the lens of the eye. For such purposes, a so-called aberrometer is needed, a device for measuring the total distortion of light in the eye.




It should be understood that the measurement of the surface and refraction of the eye is repeated several times in order to avoid the possibility of errors. Based on the data obtained, the attending surgeon chooses the best one from all the available topography maps and compares the data with the subjective selection of glasses in order to find the best compromise between them. All this requires both time and experience of the surgeon in order to accurately compensate for all existing irregularities that affect poor visual acuity. When the surgeon makes a choice, the data is loaded into the laser and performed with both superficial and flap-types of laser vision correction. Now we understand why clinics often inflate prices for this method of surgery.




 


Attention! If you have more recent information, we will be happy to accept it. If you have any questions, put it on the forum (https://findsurgery.eu/forum/) or ask directly by email info@findsurgery.eu.






Bibliography


    

  1. Sinjab MM, Cummings AB. Customized Laser Vision Correction. Springer International Publishing AG; 2018. doi:10.1007%2F978-3-319-72263-4
    2. 

  2. Li SM, Kang MT, Wang NL, Abariga SA. Wavefront excimer laser refractive surgery for adults with refractive errors (Review). Cochrane database Syst Rev. 2020;12:CD012687. doi:10.1002/14651858.CD012687.pub2
    3. 


	


	

			






	

		
Laser vision correction and other surgeries for presbyopia
	


	
		

		
	

		
From what age and when it is recommended to undergo laser vision correction for presbyopia?


By getting elder the lens of the eye loses its elasticity, which makes it difficult to focus vision at close range. At the same time, a person cannot see the fine print or small objects. All older people are at risk of presbyopia, mostly from 45 years of age. Clinical research and patient demand has resulted in more and more individualized treatments for presbyopia in recent years 1 2 3 4 5. Presbyopic corneal correction techniques (not intraocular lenses) can be categorized as 6 7:


    

  • monovision,
    • 

  • laser multifocal vision correction,
    • 

  • intracorneal multifocality,
    • 

  • corneal segments (implants).
    • 



Laser multifocal vision correction for presbyopia has significantly increased interest in itself in recent years. The use of excimer lasers in the surgical correction of presbyopia is not new, but only recently refractive surgeons have begun to effectively combine this method of treating refractive anomalies of presbyopia. Basically, the type of laser correction of presbyopia comprises Presby-LASIK (see LASIK) and less often Presby-LASEK operations (see LASEK). When the flap is created with a femtosecond laser, this group is called Prebi-Femto-LASIK, but that doesn’t change the meaning. Next, we will analyze in more detail why Presby-LASEK is not so popular.




How is the Presby-LASIK surgery type done ?


The essence of all laser refractive surgery for presbyopia is multifocal ablation, i.e. based on the creation of two or more areas of different optical power in which the greatest visual acuity is achieved. This can be achieved by creating different cornea curvatures for distance visual acuity and near reading in different eyes (monovision) or in one eye. In monovision, the dominant eye is usually corrected for distance.




In the second case, basically, a small central optical region is created with a steeper curvature for reading and a less steep region for distance vision (see Fig. below). The number of areas can be more than 2. Here visual acuity depends on the size of the pupil 8,9. It is necessary to understand that each person has a dominant eye, which is operated so that the distance visual acuity is maximum on it. One such ablation profile for presbyopic patients has been performed with AMARIS lasers since 2007.




Presby-LASIK and other types of surgeries for presbyopia correction





One such module for Presby-LASIK with two areas of vision is PresbyMAX® of three surgeries (µ-Monovision, Hybrid, Monocular), which differ in the degree of difference in refraction between the eyes (anisometropia). There are other multifocal surgeries of this type from other manufacturers of surgeries with commercial names such as Presbyond®, Supracor ™ and CustomVue ™ VISX, however in the case of Presbyond® the central cornea is left for distance vision 10. It should be understood that a high degree of anisometropia can lead to loss of stereoscopic (spatial) vision and contrast sensitivity.




Here we can add that such operations with Presby-PRK or Presby-LASEK are rare, because there is a possibility that multifocality on the cornea may be partially covered by the processes of overgrowing of the removed epithelium (re-epithelialization). Hence, the presence of a flap excludes this possibility.








Other surgery types to correct presbyopia


Recently, IOL implantation has been chosen by an increasing number of refractive surgeons and patients due to its reversibility and a wider range of vision error correction. IOLs are considered to be more accurate and safer than laser presbyopia 11, but laser vision correction is worth considering as well. Patients undergoing posterior IOL surgery should be counseled about the risk of cataracts and the potential need for further surgery 11. Surgeons and patients should make decisions carefully according to specific situations 12.




There are the following most popular alternative treatments for presbyopia:




    

  • Reading glasses
    • 



This is a monofocal vision correction for only one specific working distance.




    

  • Progressive glasses
    • 



This is a multifocal vision correction, but here not all patients adapt to such glasses. These glasses have areas for near (reading) and distance visual acuity.




    

  • Contact lenses
    • 



This is both multifocal and monofocal vision correction. Glare and ghosting is possible with multifocal lenses.




    

  • Monofocal vision with Presby-LASIK or by replacing the lens of the eye with an intraocular lens (IOL)
    • 



In this case, both eyes are corrected for distance or near vision. Reading glasses are often needed if the patient has been operated for distance vision.




    

  • Monovision with Presby-LASIK
    • 

  • Monovision when replacing the eye lens by an IOL
    • 



In monovision, the visual acuity of the eyes is corrected at one distance only. As mentioned above, there is a possibility that not all patients get used to the significant difference in visual acuity of the distance and the near eye.




    

  • Multifocal methods for Presby-LASIK and IOL
    • 



There is also the likelihood of the above, i.e. not all patients can get used to it. One of the advantages is that this treatment covers the entire range of distances due to the different curvature of areas on the cornea. The disadvantages may include discomfort, because the quality of vision depends on the size of the pupil.





The advantage of using inlay inserts is that they can eliminate and reverse the results of treatment. Although the inserts in the cornea are located in only one eye, they differ from monovision in that they do not affect distance vision. For some inserts, light entering the eye is limited, which can reduce contrast and night vision, i.e. optical side effects may occur.




    

  • Conductive keratoplasty
    • 



Complete correction of the far eye in combination of multifocality and monovision for reading in the other eye 6.






Results after laser vision correction of prebiopia


Let’s consider clinical results after applying PresbyMAX® technique and its three modes: monocular, hybrid and µ-monovision. They differ from each other in the magnitude of refraction into the distance and must be selected individually. We will not delve into the theory, but compare the results of recent positive studies.




The results of clinics in Holland in 2020 showed that even 6 years after surgery, presbyopic treatment using hybrid and µ-monovision modes is safe and effective. Postoperative results indicate improved binocular vision for distance, near, and mid-range. To improve patient satisfaction, 8% of patients had to resort to a second course of surgery 9. Binocular Uncorrected Distance Visual Acuity (BUDVA, i.e. by two eyes)> 20/20, or one (0 according to the logMAR table), was achieved in 100% of patients. Although individually 16% of the eyes lost more than 2 lines of visual acuity compared to vision with glasses before surgery, no line was lost in the case of binocular vision after 6 years.




One of the latest studies 8 of the same 2020 of the same PresbyMAX® technique for patients from 42 to 62 years old in the People’s Republic of China, but a monocular mode, has shown its safety and efficacy for correcting presbyopia and that it can improve vision both at far and near distance. However, deterioration in the quality of vision can occur at an early stage, but gradually recover to the preoperative level. All patients had binocular vision (vision with two eyes) more than 100% at a distance of more than 100% after 12 months (≥ 20/20 according to Snellen chart or  ≤ 0.0 according to the logMAR table, or more than 10 lines according to the Sivtsev’s table). Binocular near visual acuity of more than 100% was achieved in almost 78% of patients. Preservation of visual acuity after eye correction remained at a high level, because no one has lost more than 2 lines.




The PresbyMAX® monocular mode in study 13 of the same year 2020 showed that it can provide a quick recovery of vision, and therefore is recommended for people with increased demands for distance vision. Patients over 40 years old showed stable refraction during the following 2 years. Binocular uncorrected distance visual acuity (BUDVA) remained ≥ 20/25 or 80% (0.1 acc. the logMAR table), and binocular uncorrected near visual acuity (for reading) (BUNVA) > 20/25 remained in 90.9% of patients. Here, too, none of the patients lost more than 2 lines of visual acuity compared to visual acuity with glasses before the operation.




The study results 14 of 2019 from clinic in Spain using one of the currently popular PresbyMAX® modes (µ-Monovision) showed a good stability of eye refraction after three months and three years (deviation 0.25 D).




There is also a less successful study 15 of patients over 40 years old after one year using PresbyMAX® technology (µ-Monovision and Hybrid) from Germany, dating back to 2020. Although the indicators of the achieved refraction remained quite high, i.e. a change of no more than 1 diopter was in 89% of the eyes in the dominant eye (reading vision), and 86% in the dominant eye (distance vision), but about 31% of patients lost more than 2 lines of visual acuity compared to vision with glasses before surgery.




However, the Hybrid and µ-Monovision methods with PresbyMAX® technology in 2020 showed higher results 16 after 1 year in patients from 41 to 51 years old in China. So in 99% of patients, the change in refraction was less than 1 diopter. None of the patients lost more than 2 lines of visual acuity compared to vision with glasses before surgery.




There are also results of studies from Russia after 4 years using the µ-Monovision mode in patients aged from 40 to 59, presented at an international congress in 2019 17. It was shown that the average binocular visual acuity significantly improves after surgery, stabilizes within 6 months after surgery and remains stable for at least 4 years of the follow-up.




As it has already become clear, monocular surgery with PresbyMAX® has an advantage over classical monovision in that it uses intermediate vision in the non-dominant eye and restoration of distance vision is usually achieved after about 3 months. By other PresbyMAX® modes this period is even faster.




Prospects for treating presbyopia


Implantation of a refractive lenticule can be an effective alternative to the treatment of presbyopia or to eliminate complications of LASIK 18. Despite the leading development of materials with increased biocompatibility with the cornea, the implantation of natural donor tissue, that is a refractive lenticule, can provide better diffusion of nutrients through the cornea than presbyopic inserts (implants). Implantation of the lenticule can provide an inexpensive alternative to synthetic material that is associated with subsequent opacification, fibrosis (proliferation of connective tissue), or abnormal corneal shape 18. After natural tissue implantation, the corneal shape remains more natural compared to laser treatment.


 


Attention! If you have more recent information, we will be happy to accept it. If you have any questions, put it on the forum (https://findsurgery.eu/forum/) or ask directly by email info@findsurgery.eu.






Bibliography


    

  1. Uthoff D, Pölzl M, Hepper D, Holland D. A new method of cornea modulation with excimer laser for simultaneous correction of presbyopia and ametropia. Graefe’s Arch Clin Exp Ophthalmol. 2012;250(11):1649-1661. doi:10.1007/s00417-012-1948-1
    2. 

  2. P B, F P, S. AM. Uncorrected binocular performance after biaspheric ablation profile (PresbyMAX) for presbyopic corneal treatment. Am J Ophthalmol. 2013. doi:10.1016/j.ajo.2013.07.005
    3. 

  3. Luger MHA, Ewering T, Arba-Mosquera S. One-year experience in presbyopia correction with biaspheric multifocal central presbyopia laser in situ keratomileusis. Cornea. 2013;32(5):644-652. doi:10.1097/ICO.0b013e31825f02f5
    4. 

  4. Luger MHA, Ewering T, Arba-Mosquera S. 3-Month experience in presbyopic correction with bi-aspheric multifocal central presbyLASIK treatments for hyperopia and myopia with or without astigmatism. J Optom. 2012;5(1):9-23. doi:10.1016/j.optom.2011.12.001
    5. 

  5. Iribarne Y, Juárez E, Orbegozo J, Saiz Á, Mosquera SA. Bi-aspheric ablation profile for presbyopic hyperopic corneal treatments using AMARIS with PresbyMAX module : Multicentric Study in Spain. 2012:5-16.
    6. 

  6. Arba Mosquera S, Alió JL. Presbyopic correction on the cornea. Eye Vis (London, England). 2014;1:5. doi:10.1186/s40662-014-0005-z
    7. 

  7. Higginbotham J. Correcting Presbyopia – Modern Options Head of Clinical Affairs What is Presbyopia ? Birmingham Opt. 2016:44. https://de.slideshare.net/JasonHigginbotham/correcting-presbyopia-modern-options.
    8. 

  8. Fu D, Zhao J, Zhou X-T. Objective optical quality and visual outcomes after the PresbyMAX monocular ablation profile. Int J Ophthalmol. 2020;13(7):1060-1065. doi:10.18240/ijo.2020.07.07
    9. 

  9. Luger MHA, McAlinden C, Buckhurst PJ, Wolffsohn JS, Verma S, Arba-Mosquera S. Long-term outcomes after LASIK using a hybrid bi-aspheric micro-monovision ablation profile for presbyopia correction. J Refract Surg. 2020;36(2):89-96. doi:10.3928/1081597X-20200102-01
    10. 

  10. Sinjab MM, Cummings AB. Customized Laser Vision Correction. Springer International Publishing AG; 2018. doi:10.1007%2F978-3-319-72263-4
    11. 

  11. Barsam A, Allan BD. Excimer laser refractive surgery versus phakic intraocular lenses for the correction of moderate to high myopia. Cochrane Database Syst Rev. 2012;(5):CD007679. doi:10.1002/14651858.CD007679.pub2
    12. 

  12. Chen H, Liu Y, Niu G, Ma J. Excimer Laser Versus Phakic Intraocular Lenses for Myopia and Astigmatism: A Meta-Analysis of Randomized Controlled Trials. Eye Contact Lens. 2018;44(3):137-143. doi:10.1097/ICL.0000000000000327
    13. 

  13. Fu D, Zhao J, Zeng L, Zhou X. One Year Outcome and Satisfaction of Presbyopia Correction Using the PresbyMAX® Monocular Ablation Profile. Front Med. 2020;7(November):1-8. doi:10.3389/fmed.2020.589275
    14. 

  14. Villanueva A, Vargas V, Mas D, Torky M, Alió JL. Long-term corneal multifocal stability following a presbyLASIK technique analysed by a light propagation algorithm. Clin Exp Optom. 2019;102(5):496-500. doi:10.1111/cxo.12883
    15. 

  15. Kohnen T, Myriam B, Herzog M, Hemkeppler E. Near visual acuity and patient-reported outcomes in presbyopic patients after bilateral multifocal aspheric laser in situ keratomileusis excimer laser surgery. J Cataract Refract Surg. 2020;46:944-952.
    16. 

  16. Liu F, Zhang T, Liu Q. One year results of presbyLASIK using hybrid bi-aspheric micro-monovision ablation profile in correction of presbyopia and myopic astigmatism. Int J Ophthalmol. 2020;13(2):271-277. doi:10.18240/ijo.2020.02.11
    17. 

  17. Eskina EN. CORRECTING PRESBYOPIA USING BI-ASPHERIC MULTIFOCAL ABLATION PROFILE RELATED TO THIS PRESENTATION. ESCRS 2019, Paris. 2019.
    18. 

  18. Lazaridis A, Messerschmidt-Roth A, Sekundo W, Schulze S. Refractive lenticule implantation for correction of Ametropia: Case reports and literature review. Klin Monbl Augenheilkd. 2017;234(1):77-89. doi:10.1055/s-0042-117280
    19. 


	


	

			






	

		
Laser eye surgery treatments to improve visual acuity
	


	
		

		
	

		
Laser eye surgery treatments may be divided into therapeutic and refractive groups depending on whether the goal is to improve or safe visual acuity. The main goal of refractive surgeries is to improve the refractive effect without creating new optical problems in the eye. For example, in order to correct myopia it is necessary to reduce the refractive power of the eye either by reducing the curvature of the corneal surface, or by introducing a silicone intraocular lens (IOL) of the required power. The second option, as a rule, is used for high diopters or for diseases of the lens (cataract). There are several surgical methods available to treat ametropia (e.g. myopia, hyperopia). These techniques are broadly divided into two groups 1: those related to surgery on the cornea (refractive surgery of the cornea) and those related to surgery of the eye lens (lens refractive surgery).


Eye surgery types for vision correction


Fig. 1. Refractive and therapeutic eye surgery types




    

  • Eye flap surgeries use a blade or a femtosecond laser to create a thin flap on the surface of the cornea. The two main surgical methods used are LASer In-situ Keratomileisis (LASIK) (read more about LASIK) and PhotoRefractive Keratectomy (PRK)2 (read more about PRK). The flap treatment is called LASIK. If an incision (the cut) in the corneal stroma is created with a femtosecond laser instead of a mechanical blade a microkeratome, then LASIK is called Femto-LASIK. It is worth mentioning that a mechanical microkeratome is a thin scalpel driven by a mini electric motor. It is put on a ring, which is fixed on the eye by means of a vacuum and is controlled by the surgeon by pressing the pedal. A hinge is left on one side of the flap to fold the flap back and open the eye stroma. After that, the refractive procedure is performed by evaporation (ablation) of the corneal tissue with an ultraviolet laser source (excimer laser visual acuity correction). The laser beam vaporizes the corneal tissue without damaging the stroma. At the end of the surgery, the flap is returned to its original position to remain for healing in the postoperative period. The flap remains in place by natural fusion until the epithelium is completely healed.
    • 





    

  • In another type of laser eye surgery (Epi-LASIK), when using a mechanical microkeratome, the thickness of the flap corresponds to the epithelium thickness (less than 60 µm) 3. Here the epithelium is folded back after laser ablation. Since Epi-LASIK does not make a section in the corneal stroma, it is possible to avoid complications associated with superficial laser visual acuity correction including epithelial ingrowth, infections, etc. 4
    • 





    

  • The first step in the PRK procedure is to remove the epithelial layer by physical scraping or peeling. For this, an instrument resembling a miniature hockey stick is used. The second stage of the procedure is the evaporation of a cornea part (ablation) 5. The laser is applied on the surface of the cornea, known as the stroma, and changes its shape (curvature), therefore correcting visual errors 2. Later, the surface of the cornea without epithelium (the upper layer of the cornea is about 6 hundredths of a millimeter) is left to heal naturally with a contact lens 2.
    • 





    

  • In the LASEK operation, the necessary part of the epithelium may be not entirely removed, but folded back onto the stroma. In PRK operations, the epithelium is removed, regardless of whether it was “scraped” mechanically or with the help of alcohol. In both PRK and LASEK operations the separation of the epithelial “surface” can be carried out by applying an alcohol solution to the cornea for mechanical ablation.
    • 





    

  • Transepithelial PhotoRefractive Keratectomy (TransPRK) is a simplified one-stage PRK (read more about TransPRK). Here, the epithelium as well as a part of the stroma (the main layer under the epithelium), is removed by a laser without mechanical scraping of the epithelium with an instrument resembling a hockey stick or a rotating mechanical brush. Chemical agents such as dilute ethanol solution 6,7 8 can be used to remove corneal epithelium . Total treatment usually takes less than 30 seconds depending on the number of diopters. Removing the epithelium with a laser smoothes the surface of the cornea, which can affect the clinical results 9. Here you need to understand that the epithelium, covering the cornea, masks its microroughness.
    • 





    

  • The aim of all laser refractive operations for presbyopia (Presby-LASIK and Femto-Presby-LASIK) (read more about Presby-LASIK) is multifocal ablation, i.e. based on the creation of two or more optical areas in which the best visual acuity is achieved. This can be achieved by creating different curvatures of the cornea for distance acuity and near reading in different eyes (monovision) or in one eye. In monovision, the dominant eye is usually corrected for distance. In the second case (one eye), an optical region is created with a steeper curvature for reading and a less steep region for distance vision. The number of areas can be more than 2. Here visual acuity depends on the size of the pupil 10,11. It should be understood that each person has a dominant eye, which is treated so that the visual acuity in the distance is achieved on it by the best approach.
    • 





    

  • SMILE® corneal lenticule extraction is the first of the corneal lenticule extraction technologies, which has existed for almost 15 years 12 13. In theory, it is a flapless refractive corneal operation or vision correction using only a femtosecond laser system 14. Here refractive correction is achieved by removing part of the corneal tissue. In the first step a femtosecond laser creates an intrastromal lenticule (a detached layer) inside the cornea. For this, a contact element (patient interface) touches the eye using a vacuum for stability during laser operation. In the second stage, two “pockets” are prepared with a special instrument (dissector) above and below the lenticule. After that, the lenticule is removed with tweezers in common (read more about lenticule extraction).
    • 





    

  • Methods where synthetic materials (implants) are inserted into the cornea to reshape the cornea include intracorneal inlays and rings for treating presbyopia and segments for corneal diseases (e.g. keratoconus) 2 15. Unlike Implantable Collamer (also Contact) Lenses (ICL) and Intraocular Lenses (IOL), which are implanted behind the cornea in the posterior chamber of the eye, the implants are inserted into the incision made in the cornea.
    • 





    

  • It shall be mentioned, that in general therapeutic surgeries are applied in case of preventing progression or formation of keratoconus (type of ectasia or bulging out cornea), scars or need of corneal transplantation. The name CorssLinking means a minimally invasive treatment, where a combination of ultraviolet light and a solution containing vitamin B2 (Riboflavin) forms additional bonds between molecules of the cornea, i.e. strengthens it. In case of following corneal abrasions after trauma such strategy as excimer laser PhotoTherapeutic Keratectomy (PTK) is applied 16. In simple words the excimer laser deletes the part of epithelium and serves for better errosion (epithelium cells healing).
    • 





Attention! If you have more recent information, we will be happy to accept it. If you have any questions, put it on the forum (https://findsurgery.eu/forum/) or ask directly by email info@findsurgery.eu.






Bibliography


    

  1. Barsam A, Allan BD. Excimer laser refractive surgery versus phakic intraocular lenses for the correction of moderate to high myopia. Cochrane Database Syst Rev. 2012;(5):CD007679. doi:10.1002/14651858.CD007679.pub2
    2. 

  2. Shortt AJ ABDS, Evans JR. Laser assisted in situ keratomileusis (LASIK) versus photorefractive keratectomy (PRK) for myopia. Cochrane Database Syst Rev. 2013;(1). doi:10.1002/14651858.CD005135.pub3
    3. 

  3. Pallikaris I, Mcdonald MB, Cross WD, et al. A Roundtable Discussion Epi-LASIK : A Roundtable Discussion. 2005;(May).
    4. 

  4. Wen D, McAlinden C, Flitcroft I, et al. Postoperative efficacy, predictability, safety, and visual quality of laser corneal refractive surgery: a network meta-analysis. Am J Ophthalmol. 2017;178:65-78. doi:10.1016/j.ajo.2017.03.013
    5. 

  5. Golan O, Randleman JB. Pain management after photorefractive keratectomy. Curr Opin Ophthalmol. 2018;29(4):306-312. doi:10.1097/ICU.0000000000000486
    6. 

  6. Lee HK, Lee KS, Kim JK, Kim HC, Seo KR, Kim EK. Epithelial healing and clinical outcomes in excimer laser photorefractive surgery following three epithelial removal techniques: Mechanical, alcohol, and excimer laser. Am J Ophthalmol. 2005;139(1):56-63. doi:10.1016/j.ajo.2004.08.049
    7. 

  7. Aslanides IM, Padroni S, Mosquera SA, Ioannides A, Mukherjee A. Comparison of single-step reverse transepithelial all-surface laser ablation (ASLA) to alcohol-assisted photorefractive keratectomy. Clin Ophthalmol. 2012;6(1):973-980. doi:10.2147/OPTH.S32374
    8. 

  8. Tomás-Juan J, Larra AM, Hanneken L. Corneal Regeneration After Photorefractive Keratectomy : A Review. J Optom. 2015;8:149-169. doi:10.1016/j.optom.2014.09.001
    9. 

  9. Rechichi M. The new modified STARE-X EVO protocol for keratoconus: two years’ results of full customized transepithelial ablation and pachymetry-guided accelerated cross-linking. ESCRS 2019 Paris. 2019:47.
    10. 

  10. Fu D, Zhao J, Zhou X-T. Objective optical quality and visual outcomes after the PresbyMAX monocular ablation profile. Int J Ophthalmol. 2020;13(7):1060-1065. doi:10.18240/ijo.2020.07.07
    11. 

  11. Luger MHA, McAlinden C, Buckhurst PJ, Wolffsohn JS, Verma S, Arba-Mosquera S. Long-term outcomes after LASIK using a hybrid bi-aspheric micro-monovision ablation profile for presbyopia correction. J Refract Surg. 2020;36(2):89-96. doi:10.3928/1081597X-20200102-01
    12. 

  12. Shah R, Shah S, Sengupta S. Results of small incision lenticule extraction: All-in-one femtosecond laser refractive surgery. J Cataract Refract Surg. 2011;37(1):127-137. doi:10.1016/j.jcrs.2010.07.033
    13. 

  13. Reinstein DZ, Archer TJ, Carp G. The Surgeon’s Guide to SMILE : Small Incision Lenticule Extraction.; 2018.
    14. 

  14. Ang M, Tan D, Mehta JS. Small incision lenticule extraction (SMILE) versus laser in-situ keratomileusis (LASIK): Study protocol for a randomized, non-inferiority trial. Trials. 2012;13. doi:10.1186/1745-6215-13-75
    15. 

  15. Sakellaris D, Balidis M, Gorou O, et al. Intracorneal Ring Segment Implantation in the Management of Keratoconus: An Evidence-Based Approach. Ophthalmol Ther. 2019;8(s1):5-14. doi:10.1007/s40123-019-00211-2
    16. 

  16. Watson SL, Leung V. Interventions for recurrent corneal erosions. Cochrane Database Syst Rev. 2018;(7). doi:10.1002/14651858.CD001861.pub4
    17. 


	


	

			






	

		
LASIK eye surgery and Femto-LASIK
	


	
		

		
	

		
How is LASIK procedure and Femto-LASIK done?


 


The different types of refractive surgery have a number of individual advantages and disadvantages. Types of stromal ablation (flap surgery where the base layer of the cornea is evaporated) are usually less painful and provide faster visual recovery than superficial ablation techniques.




 


Flap eye surgery uses a blade or femtosecond laser to create a thin flap on the surface of the cornea. The two main surgical techniques used are laser keratomileusis (LASIK) and photorefractive keratectomy (PRK) 1. The flap treatment is called LASer In situ Keratomileusis (LASIK). If an incision in the corneal stroma is created with a femtosecond laser instead of a mechanical blade of a microkeratome, then LASIK eye surgery becomes Femto-LASIK eye surgery. It is worth mentioning that a mechanical microkeratome is a thin scalpel driven by a mini electric motor. It is put on a ring, which is fixed on the eye by means of a vacuum and is controlled by the surgeon by pressing a pedal. A hinge is left on one side of the flap to fold the flap back and open the eye stroma. After that, the refractive procedure is performed by ablation – evaporation of the corneal tissue with an ultraviolet laser (excimer laser vision correction). The laser beam vaporizes (ablates) the corneal tissue without damaging the stroma. At the end, the flap is returned to its original position and remains for healing in the postoperative period. The flap remains in place by natural fusion until the epithelium is completely healed.




Other types of laser vision correction with flap


 


Another variant of LASIK is Sub-Bowman’s Keratomileusis (SBK), which differs from LASIK eye surgery only in that the flap is significantly thinner. Therefore, SBR is also called “LASIK with a thin flap” 2–4, more often just LASIK. Femtosecond laser flap procedures include femtosecond extraction of the lenticule Relex® FLEx 5–7. There are also names SUPER LASIK and SUPER Femto-LASIK. Here “SUPER” or “plus” means individual (personalized or customized) laser correction, which takes into account the irregularities of the eye, necessary to eliminate more complex refractive errors. In this case, it is not enough to correct spherical vision error (defocus) or astigmatism.




LASIK eye surgery and Femto-LASIK


Fig. 1. Schematic representation of LASIK eye surgery and Femto-LASIK procedures, in which the flap is created for laser correction of the cornea under this flap. Other procedures are ablation methods on the surface of the cornea such as (Trans) PRK or LASEK.




Pros and cons of Femto-LASIK and LASIK recovery. Is LASIK safe ?


 


Desensitization of the cornea and dry eyes symptoms are the most common temporary complications after LASIK 8. These postoperative consequences occur for reasons such as damage of the corneal nerves and epithelial cells, impairment of the blinking reflex, and increased tear evaporation 9. Since Femto-LASIK creates a more accurate and predictable flap thickness than after mechanical microkeratomes (see description above), the likelihood of dry eye is reduced, and the recovery of corneal sensitivity is faster than after LASIK 10. Femtosecond-laser-LASIK-made flap creation is more predictable than mechanical microkeratome 11. On the other hand, some of the advantages of a mechanical blade microkeratome include reduced procedure duration 12 and cost.




A 2020 meta-analysis using a mechanical microkeratome for LASIK and a femtosecond laser for Femto-LASIK showed that dry eyes as an adverse event may be more common with a mechanical microkeratome (457 per 1000) than with a femtosecond laser (80 per 1000 people) 13. Temporary dry eyes and an inflammatory reaction after several days (diffuse lamellar keratitis) can be side effects after mechanical microkeratome and femtosecond laser, which are treated with tear solution or anti-inflammatory therapy for a week or more, respectively.




It is important to mention that one of the factors for successful laser surgery is the achieved laser refraction and visual acuity after 3-6 months. Dissatisfied patients may experience symptoms related to residual refraction. Improved patient-reported postoperative outcomes and high levels of satisfaction are attributed to modern lasers with improved ablation profiles, combined with experienced surgeons and rigorous preoperative examinations. This makes LASIK one of the safest and most effective procedures in laser surgery 14.




According to authoritative sources 15 16 17 18, the clinically significant refractive error in optometric practice ranges up to 0.75 D, and the spherical equivalent of refraction (SEQ) around ± 0.50 D is considered for the last follow-up visit to an ophthalmologist after a laser vision correction. However, the values of refractive errors can be assessed only taking into account the patient’s visual acuity (for example, a row number according to the Snellen’s or Sivtsev’s table for the countries of the former Commonwealth of Independent States (CIS), etc.).




Ultimately, the success of LASIK depends on how satisfied patients are with their vision. A systematic review of the world literature of results after LASIK shows that more than 95% of patients are satisfied with their results 14 19, or have a best vision of more than 100% (e.g. visual acuity 20/20 according to the Snellen’s table or 10 lines according to the Sivtsev’s table for the CIS countries).




One of the other recent scientific studies (2020) presents the results of LASIK patients who have been operated since 2003 at the age of 17 to 20 years. The results show that more than 64% of patients retained more than one (e.g. 100%) visual acuity. Also, there were no cases of degenerative diseases of the eye of the cornea, ectasia (e.g. keratoconus) 20. The recent completion of a ten-year study (2008-2019) of PRK and Femto-LASIK operations proved their safety and efficacy in the long term. However, the Femto-LASIK operation showed a slight superiority in safety and efficacy over the PRK 21.




Femto-LASIK or LASIK ? PRK vs LASIK


 


Another of the meta-analyzes showed that there were no statistically significant differences in efficacy, outcomes, or safety between Femto-LASIK and other treatments used. However, Femto-LASIK is better in predictability than any other type of eye microsurgery. Femto-LASIK tends to lead over other refractive eye surgeries in the so-called “SUCRA” rating and predictability score 22. LASIK has been shown to provide faster visual recovery than PRK and is less painful, although one year visual results after surgery are comparable 1. In another type of laser surgery Epi-LASIK, the thickness of the flap corresponds to the thickness of the epithelium (less than 60 µm) when using a mechanical microkeratome 23. Here, the epithelium is folded back after laser ablation. Since Epi-LASIK does not cut the corneal stroma, it avoids the complications associated with superficial laser vision correction including epithelial ingrowth, infections, etc. 24




High results are published after Femto-LASIK 25 and remain unchanged after 3, 5 and more years 26 27. Thus, in one study with a five-year follow-up none of the patients had postoperative keratectasia, dry eye symptoms, infectious keratitis or other complications. Other follow-ups of patients over 10 years till 2020 have demonstrated excellent safety and efficacy indicators for both types of laser surgery Femto-LASIK and PRK, where Femto-LASIK had higher efficacy rates than PRK 21.




Femto-LASIK or lenticule extraction ?


 


According to one of the latest international studies, the overall satisfaction between LASIK and SMILE lenticule extraction did not differ between groups throughout the study 28. Targeted analysis during the first postoperative week showed that compared with SMILE the recovery of corneal sensitivity after LASIK was faster, and the number of symptoms reported by the patient was less. However, already one month after surgery, there were no such differences between groups in visual symptoms and satisfaction. The results of one review indicate that the purported biomechanical advantages of a small incision after lenticule extraction over LASIK cannot be demonstrated in existing studies 6.




Is it possible to do a second vision correction after LASIK?


 


First of all, it is necessary to undergo a diagnostic examination as well as to gain eye consultation at the clinic in order to answer this question. One of the latest studies showed that after a repeated LASIK procedure for myopia and hyperopia in the period 2012-2018 (originally treated 1997-2012) 88% and 74% of patients acquired visual acuity of 20/20 or more according to the Snellen’s table (10 lines according to the Sivtsev’s table) 29, respectively.


 


Attention! If you have more recent information, we will be happy to accept it. If you have any questions, put it on the forum (https://findsurgery.eu/forum/) or ask directly by email info@findsurgery.eu.






 


Источники


    

  1. Shortt AJ ABDS, Evans JR. Laser assisted in situ keratomileusis (LASIK) versus photorefractive keratectomy (PRK) for myopia. Cochrane Database Syst Rev. 2013;(1). doi:10.1002/14651858.CD005135.pub3
    2. 

  2. Althomali TA. Comparison of microkeratome assisted sub-Bowman keratomileusis with photorefractive keratectomy. Saudi J Ophthalmol. 2017;31(1):19-24. doi:10.1016/j.sjopt.2017.01.004
    3. 

  3. Slade SG, Durrie DS, Binder PS. A Prospective, Contralateral Eye Study Comparing Thin-Flap LASIK (Sub-Bowman Keratomileusis) with Photorefractive Keratectomy. Ophthalmology. 2009;116(6):1075-1082. doi:10.1016/j.ophtha.2009.01.001
    4. 

  4. Zhang R, Sun L, Li J, Law A, Jhanji V, Zhang M. Visual and Refractive Outcomes After Sub-Bowman Keratomileusis and Transepithelial Photorefractive Keratectomy for Myopia. Eye Contact Lens. 2019;45(2):132-136. doi:10.1097/ICL.0000000000000533
    5. 

  5. Wang J-S, Xie H-T, Jia Y, Zhang M-C. Small-incision lenticule extraction versus femtosecond lenticule extraction for myopic: A systematic review and Meta-analysis. Int J Ophthalmol. 2017;10(1):115.
    6. 

  6. Raevdal P, Grauslund J, Vestergaard AH. Comparison of corneal biomechanical changes after refractive surgery by noncontact tonometry: small-incision lenticule extraction versus flap-based refractive surgery – a systematic review. Acta Ophthalmol. September 2018. doi:10.1111/aos.13906
    7. 

  7. Yan H, Gong L, Huang W, Of YP-I journal, 2017 U. Clinical outcomes of small incision lenticule extraction versus femtosecond laser-assisted LASIK for myopia: a Meta-analysis. ncbi.nlm.nih.gov. 2017. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5596231/. Accessed July 4, 2018.
    8. 

  8. He M, Huang W, Zhong X. Central corneal sensitivity after small incision lenticule extraction versus femtosecond laser-assisted LASIK for myopia: A meta-analysis of comparative studies. BMC Ophthalmol. 2015;15(1). doi:10.1186/s12886-015-0129-5
    9. 

  9. Ambrósio R, Tervo T, Wilson SE. LASIK-associated dry eye and neurotrophic epitheliopathy: pathophysiology and strategies for prevention and treatment. J Refract Surg. 2008.
    10. 

  10. Friedlaender MH. LASIK surgery using the intralase femtosecond laser. Int Ophthalmol Clin. 2006. doi:10.1097/00004397-200604630-00013
    11. 

  11. Santos AM dos, Torricelli AAM, Marino GK, et al. Femtosecond Laser-Assisted LASIK Flap Complications. J Refract Surg. 2016;32(1):52-59. doi:10.3928/1081597X-20151119-01
    12. 

  12. Kahuam-López N, Navas A, Castillo-Salgado C, Graue-Hernandez EO, Jimenez-Corona A, Ibarra A. Femtosecond laser versus mechanical microkeratome use for laser-assisted in-situ keratomileusis (LASIK). Cochrane Database Syst Rev. 2018;2018(2). doi:10.1002/14651858.CD012946
    13. 

  13. N K-L, A N, C C-S, A G-HEJ-C, Ibarra A, Kahuam-López. Laser-assisted in-situ keratomileusis (LASIK) with a mechanical microkeratome compared to LASIK with a femtosecond laser for LASIK in adults with myopia or myopic astigmatism (Review). Cochrane database Syst Rev. 2020;(4):CD012946. doi:10.1002/14651858.CD012946.pub2.Copyright
    14. 

  14. Moshirfar M, Shah TJ, Skanchy DF, Linn SH, Durrie DS. Meta-analysis of the FDA Reports on Patient-Reported Outcomes Using the Three Latest Platforms for LASIK. J Refract Surg. 2017;33(6):362-368. doi:10.3928/1081597X-20161221-02
    15. 

  15. Pujol J, Ondategui-Parra JC, Badiella L, Otero C, Vilaseca M, Aldaba M. Spherical subjective refraction with a novel 3D virtual reality based system. J Optom. 2017;10(1):43-51. doi:10.1016/j.optom.2015.12.005
    16. 

  16. FDA. Study Designs of Trials in the Treatment of Myopia. Basel, Switzerland; 2003. https://webcache.googleusercontent.com/search?q=cache:QISmoWkqj3EJ:https://www.fda.gov/ohrms/dockets/ac/03/briefing/3988B1_02_Novartis%2520Briefing%2520Document.pdf+&cd=1&hl=de&ct=clnk&gl=de.
    17. 

  17. Johnstone P, Gartry D. Synopsis of Causation. Refractive Error. Dundee, London; 2008.
    18. 

  18. Sekundo W. Small Incision Lenticule Extraction (SMILE): Principles, Techniques, Complication Management, and Future Concepts. (Sekundo W, ed.). Marburg: Springer Cham Heidelberg New York Dordrecht London; 2015. doi:10.1007/978-3-319-18530-9
    19. 

  19. Kobashi H, Kamiya K, Igarashi A, Takahashi M, Shimizu K. Two years results of small incision lenticule extraction and wavefront guided laser in situ keratomileusis for Myopia. Acta Ophthalmol. 2018;96(2).
    20. 

  20. Alió del Barrio JL, Canto-Cerdán M, Bo M, Subirana N, Alió JL. Laser-assisted in situ keratomileusis long term outcomes in late adolescence. Eur J Ophthalmol. 2020. doi:10.1177/1120672120969039
    21. 

  21. Castro-Luna G, Jiménez-Rodríguez D, Pérez-Rueda A, Alaskar-Alani H. Long term follow-up safety and effectiveness of myopia refractive surgery. Int J Environ Res Public Health. 2020;17(23):1-9. doi:10.3390/ijerph17238729
    22. 

  22. Wen D, McAlinden C, Flitcroft I, et al. Postoperative Efficacy, Predictability, Safety, and Visual Quality of Laser Corneal Refractive Surgery: A Network Meta-analysis. Am J Ophthalmol. 2017;178:65-78. doi:10.1016/j.ajo.2017.03.013
    23. 

  23. Pallikaris I, Mcdonald MB, Cross WD, et al. A Roundtable Discussion Epi-LASIK : A Roundtable Discussion. 2005;(May).
    24. 

  24. Wen D, McAlinden C, Flitcroft I, et al. Postoperative efficacy, predictability, safety, and visual quality of laser corneal refractive surgery: a network meta-analysis. Am J Ophthalmol. 2017;178:65-78. doi:10.1016/j.ajo.2017.03.013
    25. 

  25. Li M, Li M, Chen Y, et al. Five-year results of small incision lenticule extraction (SMILE) and femtosecond laser LASIK (FS-LASIK) for myopia. Acta Ophthalmol. 2019;97(3):e373-e380. doi:10.1111/aos.14017
    26. 

  26. Han T, Xu Y, Han X, et al. Three-year outcomes of small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) for myopia and myopic astigmatism. Br J Ophthalmol. 2019;103(4):565-568. doi:10.1136/bjophthalmol-2018-312140
    27. 

  27. Li M, Yang D, Zhao Y, et al. Impact of ablation ratio on 5-year postoperative posterior corneal stability after refractive surgery: SMILE and FS-LASIK. Eye Vis. 2020;7(1):1-9. doi:10.1186/s40662-020-00218-y
    28. 

  28. Chiche A, Trinh L, Saada O, et al. Early recovery of quality of vision and optical performance after refractive surgery: Small-incision lenticule extraction versus laser in situ keratomileusis. J Cataract Refract Surg. 2018;44(9):1073-1079. doi:10.1016/j.jcrs.2018.06.044
    29. 

  29. Alió del Barrio JL, Hanna R, Canto-Cerdan M, Vega-Estrada A, Alió JL. Laser flap enhancement 5 to 9 years and 10 or more years after laser in situ keratomileusis: Safety and efficacy. J Cataract Refract Surg. 2019;45(10):1463-1469. doi:10.1016/j.jcrs.2019.05.030
    30. 


	


	





	

		
Myopia and myopic astigmatism in laser eye surgery
	


	
		

		
	

		
Refractive errors in human eyes, more commonly known as myopia, astigmatism and hyperopia, are the most common cases of visual impairment 1 2,3. For example, the total number of people with myopia in the world has reached 1950 million in 2010 and could exponentially reach more than 4700 million by 2050. These data indicate that by 2050, about half of the world’s inhabitants could suffer from myopia. This is primarily due to a change in genetics and the way of life of a modern person 2 3 4. As you may notice, myopia and myopic astigmatism tend to get more commonly treated in laser eye surgery.


 




Near-sightedness. Reasons


The main defining quality factors of vision are the eye lens (optical power more than 20 Diopters), curvature of the cornea (optical power more than 40 Diopters) and the length of the eyeball 5. In the emmetropic (clearly seeing) eye, light is focused in a deepening on the retina – the so-called “fovea“ (see figure below). In the fovea a clearly focused image is created, which is transmitted along the nerve fibers to the optic nerve.




Myopia, more commonly known as near-sightedness, is a condition of the eye in which the refractive power of the cornea is stronger than required to project an image on the retina, i.e., the cornea is more convex (too steep) 5. The greater the curvature of the cornea is, the greater its optical power (low and high myopia), and therefore the image from distant objects is projected not on the retina but in front of it (see figure below). As a result, the image from objects becomes blurry. Depending on the complexity of the myopia, nearby objects may be seen more clearly. Hyperopia or farsightedness is manifested in the indistinct perception of nearby objects. In this case, the image could have been projected behind the retina of the eye, but due to the lack of the ability to project it on the retina, it is simply scattered on the retina, which leads to a blurry image. In refractive surgery, myopia or general refractive astigmatism of the eye is treated by reshaping the anterior surface of the cornea (see figure below).




Myopia, astigmatism and laser eye surgery




Fig. 1. The principle of poor vision: Myopia




More often, myopia is formed due to the fact that the eye grows in adolescent period. So in most cases, myopia is formed before the age of 20 years old 6. Progressive myopia can be slowed down for children under 18 years old with the help of soft contact lenses, also special so-called orthokeratological lenses or special ophthalmic gels. Some soft contact lens (SCL) interventions for school-aged children can slow the progression of myopia (0.2 ~ 0.3 D per year) and reduce the axial length growths by about 0.10 mm per year 7. Treatment effect can last 24 months or longer. However, the mechanism of the effect of orthokeratology to slow down myopia is still unclear, although various associations and hypotheses are periodically being published 8.




Myopic Astigmatism


The cornea of a healthy eye has the same curvature in all directions, representing a flat spherical surface (X, Y in the figure below on the left).




Myopia, astigmatism and laser eye surgery




Fig. 2. Principle of poor vision. Myopic astigmatism




It should be assumed that during blinking due to the pressure of the eyelids on the cornea, as well as due to friction between eyelids and cornea, the ideal spherical shape of the cornea is disturbed. This explains one of the situations how astigmatism can occur 9 10. The cornea, as it were, acquires a shape of a cylinder.




An example of a simple correct direct myopic (near-sightedness) astigmatism is shown on the right in the figure above. It can be seen that the cornea has different curvature in two directions. In this case, there is a greater refractive power (and increased curvature) along the vertical Y meridian than along the horizontal X and this is called a with-the-rule astigmatism. With this astigmatism, the X and Y meridians are perpendicular to each other and their refractive power does not change throughout the meridian (symmetric) and is called “regular” 11. With such myopic astigmatism, the image from the stronger main meridian Y (greater curvature) is focused in front of the retina, while the image from the other major meridian X lies on the retina.




On a topographic map during a diagnostic examination, such astigmatism looks like a 90° rotated butterfly (see green colour in Fig.2).






Correction of astigmatism


The main meridians of astigmatism are determined by the optical power of refraction of the cornea. In this case, X and Y directions. Their optical power is designated by the method of their determination (keratometry) for small (K1) and large (K2) curvature of the cornea (see figure below). The difference between large and small curvature is called toricity. In this case, the visual anomaly occurs due to the too strong optical power of the Y meridian, which is more than X by two diopters.




Myopia, astigmatism and laser eye surgery




Fig. 3. Relation between eyeglass prescription and astigmatism


 




When we write a prescription for glasses or contact lenses, we use a format that allows us to describe the required optical power for the correction of myopia or hyperopia by a Sphere and for correction of astigmatism by a Cylinder with its optical axis: 0D Sph. -2D Cyl. Axis 0o. Thus, the glasses will have optical power of -2 Diopters in only one vertical direction.




Astigmatism and laser eye vision correction


The most common methods of dealing with myopia are glasses and contact lenses 12. But these conservative non-surgical methods of dealing with ametropia (myopia, hyperopia, astigmatism) are only temporary. In order to get rid of glasses, a surgical method for adults is required (see Treatments to improve vision). There are several reasons for this. One of the main ones is the ability to get rid of the wearing glasses and the painful wearing contact lenses. Wearing glasses may not be possible for certain professions, sports or other active hobbies such as fishing and hunting. Secondly, not everyone can wear contact lenses. They can be uncomfortable, not tolerated by eyes, and even unsafe in case of intense rejection by the eye 5. In the third, glasses can be associated with unacceptable aberrations (displacement of the visual rays) as the so-called glare (blindness of the patient in darkness and twilight).




When the two meridians of the cornea are at right angles, ametropia can be corrected with glasses (correct astigmatism). When the main meridians are not perpendicular, there are irregularities in them or the refractive power changes along the meridian, astigmatism is considered irregular and individual (personalized) laser correction is required (see Method of personalized (individual or customized) vision correction). Irregular astigmatism cannot be corrected with glasses or contact lenses, as the power varies along the major meridians. From a clinical point of view, the treatment of astigmatism is important in both laser vision correction and cataract surgery. Uncorrected astigmatism can lead to blurred vision, halos, etc.




The main goal of refractive surgery is to safely and predictably create a stable and desired refractive effect without introducing new optical problems. To correct myopia, it is necessary to reduce the refractive power of the eye, either by reducing the curvature of the corneal surface, or by introducing a silicone intraocular lens (IOL) of the required power. There are several surgical techniques available to treat ametropia. These techniques are broadly divided into two groups 12: those related to surgery on the cornea (refractive surgery of the cornea) and those related to surgery on the lens of the eye (lens refractive surgery) 12.




Attention! If you have more recent information, we will be happy to accept it. If you have any questions, put it on the forum (https://findsurgery.eu/forum/) or ask directly by email info@findsurgery.eu.




 


References


    

  1. Wen D, McAlinden C, Flitcroft I, et al. Postoperative Efficacy, Predictability, Safety, and Visual Quality of Laser Corneal Refractive Surgery: A Network Meta-analysis. Am J Ophthalmol. 2017;178:65-78. doi:10.1016/j.ajo.2017.03.013
    2. 

  2. Cooper J, Tkatchenko A V. A Review of Current Concepts of the Etiology and Treatment of Myopia. Eye Contact Lens. 2018;44(4):231-247. doi:10.1097/ICL.0000000000000499
    3. 

  3. Vagge A, Ferro Desideri L, Nucci P, Serafino M, Giannaccare G, Traverso CE. Prevention of Progression in Myopia: A Systematic Review. Dis (Basel, Switzerland). 2018;6(4). doi:10.3390/diseases6040092
    4. 

  4. Schaeffel F. Biological mechanisms of myopia. Ophthalmologe. 2017;114(1):5-19. doi:10.1007/s00347-016-0388-4
    5. 

  5. Shortt AJ ABDS, Evans JR. Laser assisted in situ keratomileusis (LASIK) versus photorefractive keratectomy (PRK) for myopia. Cochrane Database Syst Rev. 2013;(1). doi:10.1002/14651858.CD005135.pub3
    6. 

  6. Gwiazda J, Thorn F, Held R. Accommodation, accommodative convergence, and response AC/A ratios before and at the onset of myopia in children. Optom Vis Sci. 2005;82(4):273-278. doi:10.1097/01.OPX.0000159363.07082.7D
    7. 

  7. Li SM, Kang MT, Wu SS, et al. Studies using concentric ring bifocal and peripheral add multifocal contact lenses to slow myopia progression in school-aged children: a meta-analysis. Ophthalmic Physiol Opt. 2017;37(1):51-59. doi:10.1111/opo.12332
    8. 

  8. Li X, Friedman IB, Medow NB, Zhang C. Update on Orthokeratology in Managing Progressive Myopia in Children: Efficacy, Mechanisms, and Concerns. J Pediatr Ophthalmol Strabismus. 2017;54(3):142-148. doi:10.3928/01913913-20170106-01
    9. 

  9. Ford JG, Davis RM, Reed JW, Weaver RG, Craven TE, Tyler ME. Bilateral monocular diplopia associated with lid position during near work. Cornea. 1997;16(5):525-530. doi:10.1097/00003226-199709000-00005
    10. 

  10. Read SA, Collins MJ, Carney LG. The influence of eyelid morphology on normal corneal shape. Investig Ophthalmol Vis Sci. 2007;48(1):112-119. doi:10.1167/iovs.06-0675
    11. 

  11. Karabatsas CH, Cook SD, Sparrow JM. Proposed classification for topographic patterns seen after penetrating keratoplasty. Br J Ophthalmol. 1999;83(4):403-409. doi:10.1136/bjo.83.4.403
    12. 

  12. Barsam A, Allan BD. Excimer laser refractive surgery versus phakic intraocular lenses for the correction of moderate to high myopia. Cochrane Database Syst Rev. 2012;(5):CD007679. doi:10.1002/14651858.CD007679.pub2
    13. 


	


	

			






	

		
Transepithelial PRK
	


	
		

		
	

		


Methods for superficial excimer laser vision correction include transepithelial photorefractive keratectomy (TransFRK), laser epithelial keratomileusis (LASEK) and in situ epi-laser keratomileusis (Epi-LASIK). Stromal corneal ablation procedures include laser keratomileusis “in situ” with a flap (LASIK, i.e. Laser-in-situ-Keratomileusis), created mechanically or with a femtosecond laser (Femto-LASIK). Corneal lenticular extraction procedures have several commercial names depending on the manufacturer. The first femtosecond extraction of the leticula (corneal layer) using a flap has got the trade name given by the manufacturer ReLEx FLEx® 1 (Refractive Lenticule Extraction – Femtosecond lenticule extraction). Later, the small incision (cut) lenticule extraction was called ReLEx SMILE® 1 2. There are now several similar surgeries from other manufacturers such as SmartSight® 3, CLEAR 4 (Corneal Lenticule Extraction for Advanced Refractive Correction). Of course, it makes sense to believe that this number of surgeries will increase with time.


 




What is TransEpithelial PRK or TransPRK (also Trans-PRK) ?


 


 




Transepithelial photorefractive keratectomy is a simplified one-stage PRK (read more about PRK). Here, the epithelium, as well as part of the stroma (the main layer under the epithelium), is removed by a laser without mechanical scraping of the epithelium with an instrument resembling a hockey stick or a rotating brush. Chemical agents such as dilute ethanol 5, 6 7 can be used to remove corneal epithelium. The total laser treatment usually takes less than 30 seconds, depending on the number of diopters. Removing the epithelium with a laser smoothes the cornea surface which can affect the clinical results 8. Here you need to understand that the epithelium covering the cornea masks its surface with microroughness.






Features of TransPRK


Transepithelial photorefractive keratectomy (TransFRK) emerged as a modification of its predecessor PRK, and replaced mechanical and chemical cleaning of the corneal epithelium with a laser 9. As in PRK, one of the main inconveniences after Trans-PRK compared to LASIK is postoperative pain until the epithelium is overgrown 10. After TransFRK, similarly to PRK, soft contact lenses are widely used as a dressing to reduce pain and optimize the healing process of the epithelium 11. Although the tear film between the lens and the cornea is only about 1–2 µm thick, this facilitates the penetration of postoperative drugs into the cornea (anti-inflammatory eye drops, topical steroids, etc.). For example, soft contact lenses impregnated with a non-steroidal anti-inflammatory drugs have long been shown to be effective in reducing pain without compromising visual results 12.




Results after TransFRK


One of the first studies (2004) comparing epithelial healing, postoperative pain and visual results after epithelial-mechanical (conventional PRK), transepithelial PRK, and subepithelial keratomileusis (LASEK) after 6 months failed to find significant differences between the 3 methods. In other words, the results of corneal pain and the degree of corneal opacity were fairly similar 5. Later, in 2012, transepithelial ablation was shown to be safer than mechanical scraping of the epithelium using chemical agents such as alcohol. It has been demonstrated that TransPRK provides faster epithelial healing, less postoperative pain and less corneal opacity at 1 week, 1, 3 and 6 months after surgery 6. But it should be understood that other technologies are also not standing still and are being improved.




One large meta-analysis of the 16 most recent known studies of 1924 eyes after transepithelial PRK was published in 2020 9. The included studies were published by authors from South Korea, Iran, Turkey, People’s Republic of China, the Netherlands, Greece, Lebanon, Poland, and Saudi Arabia. The period of postoperative follow-up ranged from 3 to 18 months until 2019.




Here, characteristics such as clinical efficacy, safety and predictability of clinical results were tested. To understand these results, it is necessary to mention what these characteristics mean. Thus, efficacy was defined as the proportion of treated eyes with postoperative distance visual acuity (UDVA) ≥ 20/20 (or 10 lines according to the Sivtsev’s table). Predictability is the proportion of all eyes with a deviation from the target (planned) postoperative refraction of up to 0.5 diopters. Safety was interpreted as the proportion of operated eyes that lost more than 2 lines of postoperative distance visual acuity even with glasses (BDVA) according to the Snellen chart compared to visual acuity with glasses before surgery.




The results of all studies had an efficacy of more than 76% with the exception of one lower value 13. The small effectiveness of this study 13 can be explained by the fact that it also included patients with impaired distance visual acuity even with glasses before the surgery. In other words, this does not mean that this type of surgery in this study was not successful, but that the efficacy index took into account the preoperative distance visual acuity with glasses in all patients, even with complications. All 16 included studies confirmed the value of the TransPRK intervention. Thirteen studies reported 100% safety, while 13 and two others reported values ​​between 93% – 98%. In terms of predictability, the obtained results showed an average estimate of 89% (95% of estimates in the 82% – 93% confidence interval).




Thus, it has been proven that TransErithelial PRK is a useful technique of modern refractive surgery to avoid complications associated with flap, keratitis (inflammation), formation of macrostriae (micro stripes) or epithelial ingrowth 9.




In conclusion, we can conclude that Trans-PRK is a tissue-preserving laser intervention with a low risk of developing ectasia – deformity and protrusion of the cornea (the tissue is thicker because there is no flap). However, do not forget that other superficial operations like PRK and LASEK are also improving. A recent analysis at the World Congress of the European Society for Cataract and Refractive Surgeons (Winter ESCRS 2021) is an example of this 14.


 


Attention! If you have more recent information, we will be happy to accept it. If you have any questions, put it on the forum (https://findsurgery.eu/forum/) or ask directly by email info@findsurgery.eu.




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Источники


    

  1. Reinstein DZ, Archer TJ, Carp G. The Surgeon’s Guide to SMILE : Small Incision Lenticule Extraction.; 2018.
    2. 

  2. Carl Zeiss Meditec AG. ZEISS VisuMax Ideal platform for femtosecond laser solutions. https://www.zeiss.com/meditec/int/product-portfolio/refractive-lasers/femtosecond-laser-solutions/visumax.html.
    3. 

  3. SCHWIND eye-tech-solutions GmbG. CE approval for SCHWIND ATOS® and SmartSight. https://www.eye-tech-solutions.com/en/infocenter/press/ce-approval-for-schwind-atos-and-smartsight.
    4. 

  4. Ziemer Ophthalmology GmbH. CLAER. NEW: CE marked. https://www.ziemergroup.com/en/clear/.
    5. 

  5. Lee HK, Lee KS, Kim JK, Kim HC, Seo KR, Kim EK. Epithelial healing and clinical outcomes in excimer laser photorefractive surgery following three epithelial removal techniques: Mechanical, alcohol, and excimer laser. Am J Ophthalmol. 2005;139(1):56-63. doi:10.1016/j.ajo.2004.08.049
    6. 

  6. Aslanides IM, Padroni S, Mosquera SA, Ioannides A, Mukherjee A. Comparison of single-step reverse transepithelial all-surface laser ablation (ASLA) to alcohol-assisted photorefractive keratectomy. Clin Ophthalmol. 2012;6(1):973-980. doi:10.2147/OPTH.S32374
    7. 

  7. Tomás-Juan J, Larra AM, Hanneken L. Corneal Regeneration After Photorefractive Keratectomy : A Review. J Optom. 2015;8:149-169. doi:10.1016/j.optom.2014.09.001
    8. 

  8. Rechichi M. The new modified STARE-X EVO protocol for keratoconus: two years’ results of full customized transepithelial ablation and pachymetry-guided accelerated cross-linking. ESCRS 2019 Paris. 2019:47.
    9. 

  9. Sabau A, Daas L, Behkit A, et al. Efficacy, Safety and Predictability of Transepithelial Photorefractive Keratectomy – a Meta-Analysis. Vol Publish Ah.; 2020. doi:10.1097/j.jcrs.0000000000000487
    10. 

  10. María Clara Arbelaez. Pain control in TransPRK. ESCRS 2019 Paris. 2019:20.
    11. 

  11. Cherry PM. The treatment of pain following excimer laser photorefractive keratectomy: additive effect of local anesthetic drops, topical diclofenac, and bandage soft contact. Ophthalmic Surg Lasers. 1996;27:S477-S480.
    12. 

  12. Solomon KD, Donnenfeld ED, Raizman M, et al. Safety and efficacy of ketorolac tromethamine 0.4% ophthalmic solution in post-photorefractive keratectomy patients. J Cataract Refract Surg. 2004;30(8):1653-1660. doi:10.1016/j.jcrs.2004.05.019
    13. 

  13. Gershoni A, Mimouni M, Livny E, Ophthalmology IB-I, 2018 U. Z-LASIK and Trans-PRK for correction of high-grade myopia: safety, efficacy, predictability and clinical outcomes. Int Ophthalmol. 2019;39:753-763. https://link.springer.com/article/10.1007/s10792-018-0868-4. Accessed July 3, 2018.
    14. 

  14. J. Hjordal. Surface ablation techniques. Winter ESCRS 2021. 2021:21.
    15. 


	


	





	

		
Corneal Lenticule Extraction
	


	
		

		
	

		


FemtoSecond Laser and Femtolaser Eye Surgery


The introduction of the femtosecond laser into refractive surgery has made it possible to create corneal flaps in a more precise, stable and safer way 1. Since their first clinical use in 2001 in the LASIK flap, femtosecond lasers have consistently taken the place of the dominant flap technology worldwide, i.e. LASIK, due to their reproducibility, safety, accuracy and versatility 2.




The process of cutting the cornea with a femtosecond laser by ultrashort pulses (tens of 1/1015 seconds) is also known as photodisruption or photomechanical (photoacoustic) damage 3. Hot plasma is created inside the cornea at the absorption point of the femtosecond laser pulse. Subsequently, this plasma propagates (expands) in the form of a supersonic wave forming a cavitation bubble 4 5. In other words, extremely short pulses lead to surgical separation of the corneal tissue with minimal concomitant damage. Many bubbles, one after the other, create a cut.




Although the origin of this technique goes back to 1995 with the first patents 6, for a long time only one platform was available to perform this kind of procedure 7. Since 2019, other companies have started to enter the market with similar proposals. Corneal lenticular extraction procedures have several commercial names depending on the manufacturer. This is the first femtosecond extraction of the leticule (corneal layer) using a flap, the commercial name given by the manufacturer was ReLEx FLEx® 8. Later, ReLEx SMILE® 8 9 was called Small Incision (cut) Lenticule Extraction. There are now several similar operations from other manufacturers such as SmartSight® 10, CLEAR 11 (Corneal Lenticule Extraction for Advanced Refraction). Of course, it makes sense to believe that this number of operations will increase.




What is corneal lenticular extraction ?


Small incision lenticule extraction or SMILE is the first corneal lenticular extraction technology that has existed for almost 15 years 12. In theory, it is a flapless refractive corneal operation or vision correction using only a femtosecond laser system 13. Refractive correction is achieved by removing corneal tissue.




In the first step, a femtosecond laser creates an intrastromal lenticule (a detached layer) inside the cornea. For this, a contact element (patient interface) docks on (contacts) an eye using a vacuum for stability during laser operation. In the second stage, two “pockets” are prepared with a special instrument (dissector) above and below the lenticule. After that, the lenticle is removed with tweezers (see video).




Following the introduction in 2007 of the VisuMax® femtosecond laser 14, one of the first operations to remove the lenticule to correct myopia by flap formation (FLEX) was performed. This procedure was followed by the SMILE procedure (removal of the lenticule through a small incision). Because of eliminating the need for a flap on the surface of the cornea, SMILE damages fewer corneal nerves and has the potential to preserve more original corneal biomechanics than (Femto-)LASIK 15. In this technique the lenticule is selected through a lateral incision of 2.0 to 4.0 mm, which is much shorter than the LASIK flap15. The duration of the laser eye surgery




How long does laser eye of lenticule extraction surgery last ?


The eye contact with the PI during the surgery is typically less than 5 minutes. Patient lies on a patient

bed. To ensure adequate suction prior to and throughout the surgery the surgeon

shall optimize the eye position along the X and Y axes as the eye is brought closer to the laser contact

element. The duration of this step for lenticule surgery depends on the experience of the surgeon. The necessary suction level on the patient’s eye is achieved in several seconds. Then the start of the lenticule’s creation shall be confirmed.




The max duration of applied vacuum to the patient interface is usually less than 2 minutes. Application

of lower IntraOcular Presuure decreases the probability of intraocular pressure complications.

Thus, it shall be kept as short as possible. The laser portion  takes from 30 seconds to one minute that is roughly twice the duration to complete the flap cuts during Femto-LASIK 16. The duration of the photodisruption procedure shall almost not depend on the refractive error and remain the same if other lenticule and cap parameters remain unchanged. The entire procedure, including the removal of the corneal tissue, generally takes 10 to 20 minutes in total and is strictly dependent on the experience of the surgeon.




Benefits of corneal lenticule extraction


    

  • It is a “flapless” (no flap) and painless procedure, which means that there is no risk of loss of vision quality for the patient due to complications with the flap with (Femto-)LASIK 16.
    • 

  • The lifestyle or profession of patients sometimes contraindicates LASIK due to the flap. The type of surgery with extraction of the lenticule has a minimum of restrictions and maximum postoperative comfort. Corneal extraction provides a fast way back to sport. Since surgery is minimal here, patients can return to sports almost immediately after surgery. The risk of complications due to the potential bacterial invasion (for swimmers) is also close to zero.
    • 

  • Makeup after laser vision correction? Because of the small incision and consecutive less chance of infection in the cornea, makeup can be applied soon after corneal lenticule extraction. The access of microbes or bacteria to the structure of the cornea is minimized as much as possible 16.
    • 

  • A minimum incision size of a few millimeters for lenticule extraction ensures corneal integrity and biomechanical stability 17. Review results suggest that SMILE has less impact on corneal viscoelastic properties. However, the putative biomechanical advantage in the cornea after SMILE has not been demonstrated by non-contact air tonometry (intraocular pressure measurement) in nine studies 17.
    • 

  • Vision restoration is almost the same as in LASIK and much faster than after PRK. After a few days almost all patients have high preoperative visual acuity.
    • 

  • Sufficient patient comfort on postoperative days compared to other surgical methods due to minimal corneal response 16.
    • 

  • Since the corneal nerves are partially responsible for the production of tears and lacrimal secretion is minimally impaired, the likelihood of postoperative dryness is less than 16.
    • 

  • When working with a femtosecond laser, there is no evaporation of the cornea, and therefore no smell. This benefit can be appreciated by odor-sensitive patients 16.
    • 





Before SMILE entered the market, PRK was the only solution for military, firefighters, police officers and contact sportsmen, which requires no work or sports for some time after surgery.




Clinical results after corneal lenticule extraction vs risks of laser eye surgery


In a 2019 study, results from 622 eyes demonstrated that SMILE provides effective, predictable, stable and safe vision correction in patients with myopia and astigmatism 18. 6 months after the surgery, 95% of eyes had visual acuity greater than 1 (20/20 according to the Snellen chart or 10 lines according to Sivtsev’s table). It is noteworthy that the deterioration in visual acuity after surgery compared with preoperative Corrected Distance Visual Acuity (CDVA) in most eyes was from 20/16 to 20/20, i.e. deterioration is not less than one. At 6 months, all SMILE-treated eyes with astigmatism were within ± 1.00 D, and 92% of the eyes were within ± 0.50 D (achieved refractive target versus target).




From March 2018 to July 2020 a comprehensive search was carried out in international scientific libraries and several non-English language databases. This meta-analysis included twelve studies involving 1400 eyes from 766 patients, of whom 748 underwent SMILE. This analysis showed that postoperative distance visual acuity is 20/20 with 95% probability in the long term 19.




SMILE results show remarkable stability over 3 years 1,15,20–24 and more than 88% of the refractive index results of patients after SMILE remain within ± 0.5 D 22. In theory, stronger vision correction (deeper laser intervention in cornea) is possible with SMILE without the additional risk of ectasia (deformity, bulging of the cornea), but again in theory. However, there are at least several reports in the literature about such cases caused after SMILE 25 26 27. Results of the meta-analysis collected worldwide from different countries, including Germany, Switzerland, France, China, Turkey, India, etc. 1,15,20–23,28, state that temporary dry eye after SMILE can occur 23 29. However, SMILE is relatively safe, which is also associated with fewer dry eye symptoms than after (Femto-)LASIK 23 24.




Therefore, like after LASIK, patients scheduled for lenticule removal should be informed about the risk of dry eye symptom and potential visual symptoms. For example, ghosting, fogging or focusing problems can temporarily impair the quality of vision during the first postoperative week. However, there are no further significant differences in the overall satisfaction score between corneal lenticule extraction and other types of surgery 30.




Extraction of the cornea may offer a much faster recovery of vision than PRK 31. Some study also reported fewer dry eyes in the postoperative period and faster recovery of corneal sensitivity using the corneal extraction technique compared to LASIK 32, as well as better regeneration of the corneal nerves in the postoperative period compared to LASIK 33.




Prospects for corneal lenticule extraction


Studies show that the procedure for corneal lenticule extraction can be reversed. Donor lenticules (layers of the cornea) have been successfully implanted to eliminate myopia, treat presbyopia, hyperopia and keratoconus. The use of stromal lenticules is also described for therapeutic purposes, in which the lenticule is transplanted under the flap in cases of excessive removal of stromal tissue by LASIK 34. Implantation of a refractive lenticule (RL) can be an effective alternative to Presbyopic Corneal Inlays (PCI) 34, providing better diffusion nutrients through the cornea. Synthetic PCI is often associated with subsequent opacification or even fibrosis (scarring). After RL implantation for the treatment of hyperopia, the corneal shape remains more natural 34.


 


Attention! If you have more recent information, we will be happy to accept it. If you have any questions, put it on the forum (https://findsurgery.eu/forum/) or ask directly by email info@findsurgery.eu.




Нажмите ссылку, чтобы читать эту статью на русском языке.


 


 


Источники


    

  1. Wen D, McAlinden C, Flitcroft I, et al. Postoperative Efficacy, Predictability, Safety, and Visual Quality of Laser Corneal Refractive Surgery: A Network Meta-analysis. Am J Ophthalmol. 2017;178:65-78. doi:10.1016/j.ajo.2017.03.013
    2. 

  2. Kymionis GD, Kankariya VP, Plaka AD, Reinstein DZ. Femtosecond laser technology in corneal refractive surgery: a review. J Refract Surg. 2012;28(12):912-920. doi:10.3928/1081597X-20121116-01
    3. 

  3. Donaldson KE, Braga-mele R, Cabot F, et al. Femtosecond laser – assisted cataract surgery. J Cart Refract Surg. 2013;39(11):1753-1763. doi:10.1016/j.jcrs.2013.09.002
    4. 

  4. Pepose BYJ a YS, Lubatschowski H. Comparing Femtosecond Lasers. Cataract Refract Surg Today. 2008;(OCTOBER):45-51.
    5. 

  5. Lubatschowski H, Krueger RR, Smadja D. Femtosecond Laser Fundamentals. In: Textbook of Refractive Laser Assisted Cataract Surgery (ReLACS). New York, NY: Springer New York; 2013:17-37. doi:10.1007/978-1-4614-1010-2_3
    6. 

  6. Method for corneal laser surgery. https://worldwide.espacenet.com/publicationDetails/biblio?DB=worldwide.espacenet.com&II=3&ND=3&adjacent=true&locale=en_EP&FT=D&date=20000829&CC=US&NR=6110166A&KC=A#. Accessed February 22, 2018.
    7. 

  7. Blum M, Täubig K, Gruhn C, Sekundo W, Kunert KS. Five-year results of Small Incision Lenticule Extraction (ReLEx SMILE). Cornea. 2016;0:1-4. doi:10.1136/bjophthalmol-2015-306822
    8. 

  8. Reinstein DZ, Archer TJ, Carp G. The Surgeon’s Guide to SMILE : Small Incision Lenticule Extraction.; 2018.
    9. 

  9. Carl Zeiss Meditec AG. ZEISS VisuMax Ideal platform for femtosecond laser solutions. https://www.zeiss.com/meditec/int/product-portfolio/refractive-lasers/femtosecond-laser-solutions/visumax.html.
    10. 

  10. SCHWIND eye-tech-solutions GmbG. CE approval for SCHWIND ATOS® and SmartSight. https://www.eye-tech-solutions.com/en/infocenter/press/ce-approval-for-schwind-atos-and-smartsight.
    11. 

  11. Ziemer Ophthalmology GmbH. CLAER. NEW: CE marked. https://www.ziemergroup.com/en/clear/.
    12. 

  12. Shah R, Shah S, Sengupta S. Results of small incision lenticule extraction: All-in-one femtosecond laser refractive surgery. J Cataract Refract Surg. 2011;37(1):127-137. doi:10.1016/j.jcrs.2010.07.033
    13. 

  13. Ang M, Tan D, Mehta JS. Small incision lenticule extraction (SMILE) versus laser in-situ keratomileusis (LASIK): Study protocol for a randomized, non-inferiority trial. Trials. 2012;13. doi:10.1186/1745-6215-13-75
    14. 

  14. Reinstein DZ, Archer TJ, Gobbe M, Johnson N. Accuracy and reproducibility of artemis central flap thickness and visual outcomes of LASIK with the Carl Zeiss Meditec VisuMax femtosecond laser and MEL 80 excimer laser platforms. J Refract Surg. 2010;26(2):107-119. doi:10.3928/1081597X-20100121-06
    15. 

  15. He M, Huang W, Zhong X. Central corneal sensitivity after small incision lenticule extraction versus femtosecond laser-assisted LASIK for myopia: A meta-analysis of comparative studies. BMC Ophthalmol. 2015;15(1). doi:10.1186/s12886-015-0129-5
    16. 

  16. Sekundo W. Small Incision Lenticule Extraction (SMILE): Principles, Techniques, Complication Management, and Future Concepts. (Sekundo W, ed.). Marburg: Springer Cham Heidelberg New York Dordrecht London; 2015. doi:10.1007/978-3-319-18530-9
    17. 

  17. Raevdal P, Grauslund J, Vestergaard AH. Comparison of corneal biomechanical changes after refractive surgery by noncontact tonometry: small-incision lenticule extraction versus flap-based refractive surgery – a systematic review. Acta Ophthalmol. September 2018. doi:10.1111/aos.13906
    18. 

  18. Chen P, Ye Y, Yu N, Zhang X, Zhuang J, Yu K. Correction of Astigmatism With SMILE With Axis Alignment: 6-Month Results From 622 Eyes. J Refract Surg. 2019;35(3):138-145. doi:10.3928/1081597x-20190124-02
    19. 

  19. Fu Y, Yin Y, Wu X, Li Y, Xiang A. Clinical outcomes after small-incision lenticule extraction versus femtosecond laser-assisted LASIK for high myopia : A meta-analysis. 2021:1-15. doi:10.1371/journal.pone.0242059
    20. 

  20. Kobashi H, Kamiya K, Shimizu K. Dry Eye After Small Incision Lenticule Extraction and Femtosecond Laser-Assisted LASIK: Meta-Analysis. Cornea. 2017;36(1):85-91. doi:10.1097/ICO.0000000000000999
    21. 

  21. Messerschmidt-Roth A, Sekundo W, Lazaridis A, Schulze S. Drei Jahre Nachbeobachtung nach refraktiver Small Incision Lenticule Extraction (SMILE) mit einem 500-kHz-Femtosekundenlaser im “fast Mode.” Klin Monbl Augenheilkd. 2017;234(1):102-108. doi:10.1055/s-0042-117281
    22. 

  22. Seiler T, Koller T, Wittwer V V. Limitations of SMILE (Small Incision Lenticule Extraction). Klin Monbl Augenheilkd. 2017;234(1):125-129. doi:10.1055/s-0042-123194
    23. 

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