Category: Laser Eye Surgery

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.

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. @ 180^o.

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.

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Bibliography

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

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.

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.

• Corneal segments (implants)

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. 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. 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. 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. 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. 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. 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. 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. 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. Sinjab MM, Cummings AB. Customized Laser Vision Correction. Springer International Publishing AG; 2018. doi:10.1007%2F978-3-319-72263-4
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. 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. 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. 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. 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. 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. Eskina EN. CORRECTING PRESBYOPIA USING BI-ASPHERIC MULTIFOCAL ABLATION PROFILE RELATED TO THIS PRESENTATION. ESCRS 2019, Paris. 2019.
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

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.

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

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17. Johnstone P, Gartry D. Synopsis of Causation. Refractive Error. Dundee, London; 2008.
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. 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. 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. 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. 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. Pallikaris I, Mcdonald MB, Cross WD, et al. A Roundtable Discussion Epi-LASIK : A Roundtable Discussion. 2005;(May).
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. 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. 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. 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. 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. 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

Corneal Lenticule Extraction as 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. What about Corneal Lenticule Extraction ?

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 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.

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.

How long does the 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.

See video here.

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.

 

 

Bibliography

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. 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. 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. Pepose BYJ a YS, Lubatschowski H. Comparing Femtosecond Lasers. Cataract Refract Surg Today. 2008;(OCTOBER):45-51.
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. 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. 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. Reinstein DZ, Archer TJ, Carp G. The Surgeon’s Guide to SMILE : Small Incision Lenticule Extraction.; 2018.
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. 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. Ziemer Ophthalmology GmbH. CLAER. NEW: CE marked. https://www.ziemergroup.com/en/clear/.
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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. Shen Z, Zhu Y, Song X, Yan J, Yao K. Dry Eye after Small Incision Lenticule Extraction (SMILE) versus Femtosecond Laser-Assisted in Situ Keratomileusis (FS-LASIK) for Myopia: A Meta-Analysis. PLoS One. 2016;11(12):e0168081. doi:10.1371/journal.pone.0168081
24. Zhang Y, Shen Q, Jia Y, Zhou D, Zhou J. Clinical Outcomes of SMILE and FS-LASIK Used to Treat Myopia: A Meta-analysis. J Refract Surg. 2015;32(4):256-265. doi:10.3928/1081597X-20151111-06
25. El-Naggar MT. Bilateral ectasia after femtosecond laser-assisted small-incision lenticule extraction. J Cataract Refract Surg. 2015;41(4):884-888. doi:10.1016/j.jcrs.2015.02.008
26. Wang Y, Cui C, Li Z, et al. Corneal ectasia 6.5 months after small-incision lenticule extraction. J Cataract Refract Surg. 2015;41(5):1100-1106. doi:10.1016/j.jcrs.2015.04.001
27. Sachdev G, Sachdev MS, Sachdev R, Gupta H. Unilateral corneal ectasia following small-incision lenticule extraction. J Cataract Refract Surg. 2015;41(9):2014-2018. doi:10.1016/j.jcrs.2015.08.006
28. Zhang Y, Shen Q, Jia Y, Zhou D, Zhou J. Clinical Outcomes of SMILE and FS-LASIK Used to Treat Myopia: A Meta-analysis. J Refract Surg. 2015;32(4):256-265. doi:10.3928/1081597X-20151111-06
29. Shen Z, Shi K, Yu Y, Yu X, Lin Y, Yao K. Small Incision Lenticule Extraction (SMILE) versus Femtosecond Laser-Assisted In Situ Keratomileusis (FS-LASIK) for Myopia: A Systematic Review and Meta-Analysis. PLoS One. 2016;11(7):e0158176. doi:10.1371/journal.pone.0158176
30. 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
31. Sia RK, Ryan DS, Beydoun H, et al. Visual outcomes after SMILE from the first-year experience at a U.S. military refractive surgery center and comparison with PRK and LASIK outcomes. J Cataract Refract Surg. 2020;46(7):995-1002. doi:10.1097/j.jcrs.0000000000000203
32. Cai W, Liu Q, Wei Q, et al. Dry eye and corneal sensitivity after small incision lenticule extraction and femtosecond laser-assisted in situ keratomileusis: a Meta-analysis. Int J Ophthalmol. 2017;10(4). doi:10.18240/ijo.2017.04.21
33. YC L, ASJ J, JY C, LWY Y, JS M. Cross-sectional study on corneal denervation in contralateral eyes following SMILE versus LASIK. J Refract Surg. 2020;36(10):653-660.
34. 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

The introduction of the excimer laser into the world of keratorefractive surgery in the 1990s changed the treatment of myopia, hyperopia and astigmatism forever ¹. Photorefractive keratectomy (PRK) was developed in the year 1983 using an excimer laser emitting ultraviolet light to change the curvature of the cornea. Although The United States Food and Drug Administration approved PRK as a refractive surgery method only in 1996 ². However, in recent years, the use of PRK  has shrunk due to the introduction of laser keratomileusis LASIK and later Femto-LASIK ².

Types of eye microsurgery. Treatment of myopia and hyperopia

Corneal laser surgery has become an effective alternative to glasses and contact lenses for correcting refractive errors ³. Since PRK a wide range of surgical techniques have been developed that correct the refractive errors of the eye (ametropia) by removing corneal tissue and thereby changing its curvature.

These operations can be divided into three main types:

1. PRK* (mechanically or alcohol) and LASEK (alcohol only);

* also known as MAGEK on the territory of the Russian Federation

2. Ablation of the cornea with an excimer or solid-state laser when creating a flap on its surface with an electric blade or a femtosecond laser: LASIK** and Femto-LASIK;

**also known as the REIK on the territory of the Russian Federation

3. Extraction of the corneal lenticule without and with a flap ³.

It is worth mentioning that for the first two types of operations, you can find many marketing names, which are often invented by the clinics themselves to attract more attention. These names may be neither confirmed in the scientific literature nor patented by any manufacturer. But no matter how these types of operations are presented, their principle remains unchanged.

The type of surgery with the extraction of the corneal lenticule has several commercial names, which are patented by the manufacturers of the femtosecond lasers. Of course, it should not be ruled out that clinics may also start advertising their services by replacing their proprietary names with their own for marketing purposes.

The exception is laser epithelial keratomileusis (LASEK), which historically was also called Excimer Laser Subepithelial Ablation (ELSA) ⁴. As already mentioned, in the present LASEK the epithelium is brought back onto the cornea.

How PRK and LASEK are done

The first step in the PRK procedure starts by removing the epithelial layer by physical scraping or peeling. For this, an instrument resembling a miniature hockey stick is used (“hockey knife”). In eye surgery PRK and LASEK, an epithelial flap can also be created by applying an alcohol solution to the cornea for mechanical ablation.

The second step of the procedure is the evaporation of a part of the cornea (ablation) ⁵. The laser is applied on the surface of the cornea, known as the stroma, and modifies its shape (curvature), therefore correcting visual errors ⁶. Later, the surface of the cornea without epithelium (the upper layer of the cornea of about 6 hundredths of a millimeter) left for natural healing under a contact lens ⁶. In the LASEK operation, the epithelium may not be removed, but placed back onto the stroma. In PRK operations, the epithelium is removed, regardless of whether it was “scraped” mechanically or with the use of alcohol.

In SUPER PRK and SUPER LASEK the term “SUPER” usually denotes individual (personalized) laser correction, which takes into account the peculiarities of the eye, that are needed to eliminated more complex refractive errors. In this case, it is not enough to correct only spherical vision error or astigmatism.

See video here.

Features of PRK and LASEK

PRK was the first refractive procedure using a laser and has been widely used for its safety and efficacy ⁵. In PRK the corneal epithelium is removed to facilitate stromal ablation ^{7 2}.

Today PRK surgery is often used in cases where LASIK is contraindicated, since LASIK is a “flap surgery” type, and another PRK surgery is a “surface treatment” type ⁶. For example, if the thickness of the cornea does not allow leaving the recommended minimum safe thickness of the cornea (0.25mm – 0.3mm) after changing its curvature by tissue evaporation, apart from the thickness of the flap, PRK is used. PRK corrects mild to moderate myopia, hyperopia and astigmatism with a high level of safety and efficacy ².

Although LASIK is primarily used in refractive surgery due to minor pain and rapid visual rehabilitation, LASIK is also a popular method for high myopia, thinner cornea or retinal pathology. The advantages of LASEK include the absence of possible complications associated with the flap in LASIK ⁸. The cornea is known to lead in the number of nerve endings in the human body. There are about 7000 of them per square millimeter. Therefore, removal of the epithelial layer in PRK results in a delayed healing time, slower visual recovery, and increased postoperative pain compared to LASIK ⁵.

Therefore, LASEK was developed to reduce corneal pain and opacification associated with PRK and to speed up vision recovery. Removal of the epithelium with dilute alcohol in PRK and LASEK has shown a smoother surface suitable for laser ablation ^{7, 2}. Such a surface aids in corneal healing and prevents corneal opacities (haze) ⁹ that were originally found after PRK. Recently, the problem of stromal opacification after PRK and LASEK has been significantly reduced with the introduction of new profiles of laser ablation and Mitomycin-C (MMC) ¹⁰.

On the territory of the Russian Federation, PRK with the use of Mitomycin-C is better known as MAGEK. Mitomycin-C is a solution from the group of antitumor antibiotics for suppressing division (mitosis) of epithelial cells during the healing reaction after PRK and LASEK, also used after keratoplasty (corneal transplantation) ¹⁰. Thus, MMS reduces corneal opacity and, as a consequence, improves visual acuity after PRK and LASEK ². However, new algorithms or energy settings in lasers can reduce the inflammatory response. For example, studies without MMC but using a specific excimer laser profile in Central Europe did not result in clinically significant corneal opacities ¹¹.

Epithelial cells are the first cells involved in the process of corneal regeneration after PRK, LASIK and Transepithelial PRK (see Transepithelial PRK) ^{12 2}. After removal of the epithelium for laser correction, its cells migrate from the edges of the cornea (limb) to restore the removed area ^{13,14 2}. Removal of the epithelial layer contributes to some inflammation and pain, which usually begins shortly after the PRK and LASEK treatments and continues in the first 3-5 days until the end of re-epithelialization (restoration of the removed epithelium at the sites of tissue damage). Nevertheless, the severity of this pain differs widely in patients, whereas chronic pain is much less common and is often classified by doctors and patients as symptoms of dry eye ⁵. During the healing process, the superficial epithelium and a part of the cornea may change and return to its original state. This process is called “regression”. Studies have also shown a decrease in the likelihood of its occurrence after PRK and LASEK when using MMS ^{15,16 17}.

Pain management strategies are very diverse and include techniques like cooling the cornea to reduce inflammation and suppress the perception of pain. The tissue can be cooled by washing with physiological solution (saline) or by cooling with a wet ring. Silicone hydrogel lenses, worn after surgery, allow oxygen to pass through and thus reduce pain while increase patient comfort. Also, local anesthetics (drops) applied locally are good at suppressing corneal pain. This is why this class of medication is used before surgery to numb tissues. For the best results, a contact lens is worn after surgery for mechanical protection and support for re-epithelialization in combination with the use of local non-steroidal anti-inflammatory drugs and / or diluted anesthetics. Other pain relievers can be taken in case of sudden pain ⁵.

Results after PRK and LASEK

The recent completion of a ten-year study (2008-2019) of PRK and Femto-LASIK treatments has proven their safety and effectiveness in the long term ¹⁸.

According to one study ¹⁹, LASIK suggests a higher likelihood of postoperative dry eye syndrome than PRK. On the other hand, dry eye is also associated with lower corneal sensitivity and less frequent blinking.

Another recent study ²⁰ of the results after LASEK with patients aged 18 to 37 years old using lasers from two German manufacturers showed that 100% of patients had visual acuity higher than 20/20 according to the Snellen chart, i.e. more than one (more than 10 lines according to Sivtsev’s table) in one group and more than 50% in another. After the first month, 92% of patients in the first group and 81% in the second had more than 20/20 vision, i.e. more than 10 lines according to Sivtsev’s table.

In the first weeks after LASEK surgery, the side effect of corneal opacity was noticed, but only in one eye in one of the groups. With the use of the prescribed drops, the cloudiness disappeared in the first month. 6 months after surgery, no corneal opacities were observed in any of the groups.

 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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