Safety and efficacy of Photorefractive Keratectomy (PRK) for myopia using a new corneal epithelium debridement technique

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1 ARTICLE Safety and efficacy of Photorefractive Keratectomy (PRK) for myopia using a new corneal epithelium debridement technique Rafael Bilbao-Calabuig, MD 1 ; Felix Gonzalez-Lopez, MD 1 ; Miguel A. Calvo-Arrabal,MD 1 ; Jose R Villada-Casaponsa, MD 2 ; Jaime Beltrán, MD 3 PURPOSE: To evaluate the clinical outcomes of photoreactive keratectomy (PRK) for myopia, using a new combined, ethanol-assisted and blunt mechanical corneal epithelial peeling technique. METHODS: In this prospective cases series, PRK was performed in myopic patients. A circular cellulose cell sponge soaked with 20% ethanol solution was positioned over the central cornea for 50 seconds. The adhesions between the epithelium and corneal stroma were loosened using a Weck-Cel spear, and finally, central loosened corneal epithelium was easily lifted off in a circular epitheliorhexis-like technique. Corneal photoablation was then performed using the usual nomograms and protocols for myopic surface photoablation treatments. Manifest refraction, uncorrected distance visual acuity (UDVA), and corrected distance visual acuity (CDVA) were evaluated preoperatively and postoperatively, and adverse effects were also assessed. RESULTS: The study enrolled 248 eyes of 144 consecutive patients. Mean and standard deviation of preoperative manifest refraction spherical equivalent (MRSE) was 3.73 ± 1.49 D, and mean preoperative cylinder 0.65 ± 0.71 D. After 6 months, mean decimal UDVA was 0.97 ± 0.08 and MRSE was 0.04 ± 0.33 D; postoperatively 96% of eyes had an MRSE within ±0.50 D of emmetropia. Efficacy Index was 0.99 and Safety Index Postoperative mean time for reepithelialization and contact lens removal was 5.1 ± 0.4 days, and no patient required more than 14 days of contact lens wear. No eye lost two or more lines of CDVA, or presented any significant clinical complication. Only one eye required an enhancement procedure. CONCLUSIONS: This new corneal epithelium debridement technique has been shown to be safe and effective when correcting myopia with PRK. J Emmetropia 2015; 3: Photorefractive keratectomy (PRK) is less invasive than laser in situ keratomileusis (LASIK), and seems to structurally Submitted: 07/06/2015 Revised: 08/24/2015 Accepted: 08/27/ Clínica Baviera, Instituto Oftalmológico Europeo, Madrid, Spain 2 Clínica Baviera, Instituto Oftalmológico Europeo, Albacete, Spain 3 Clínica Baviera, Instituto Oftalmológico Europeo, Valencia, Spain Financial disclosure: The authors have no commercial or proprietary interest in the products mentioned herein. Acknowledgements: Presented as an oral communication at the 32nd Congress of the European Society of Cataract and Refractive Surgery (ESCRS), London, September The authors thank Dr. Manuel Romera ( for his collaboration in producing the illustrations of the surgical procedure. Corresponding Author: Rafael Bilbao-Calabuig Clínica Baviera, Paseo Castellana, 20, Madrid 28046, Spain rbilbaocalabuig@hotmail.com weaken the cornea to a lesser degree. As a result, a trend has emerged over the last decade favouring surface ablation techniques 1,2. Several modifications of the conventional PRK procedure have been introduced in order to minimize the disadvantages of the surface ablation techniques, namely longer epithelial healing and visual recovery times, pain, and corneal haze. These alternative methods modify the means by which the corneal epithelium is removed prior to laser photoablation. Mechanical debridement (using different types of rotating brushes or scalpels), alcohol solution in laser-assisted subepithelial keratomileusis (LASEK), excimer laser in transepithelial PRK (t-prk) and an epithelial microkeratome in epi-lasik, have been extensively used to separate the corneal epithelium from the underlying anterior stroma. We recently reported a technique to peel off corneal epithelium prior to photoablation in surface ablation laser surgery that combines both a chemical and a blunt mechanical action while using very simple surgical instruments SECOIR Sociedad Española de Cirugía Ocular Implanto-Refractiva ISSN:

2 134 PRK FOR MYOPIA WITH A NEW CORNEAL EPITHELIUM DEBRIDEMENT TECHNIQUE The aim of the present study was to assess the clinical and refractive outcomes of PRK for myopia, using the aforementioned corneal epithelial debridement technique. MATERIALS AND METHODS This prospective interventional case series comprised 144 consecutive patients (248 eyes) who had PRK for myopia, treated for targeted emmetropia. It was performed at the Clinica Baviera (Madrid, Spain) in compliance with the tenets of Declaration of Helsinki, and had full ethical approval from the Clinica Baviera Institutional Ethics Committee. All patients provided written informed consent after receiving a full explanation of the procedure. All patients were assessed preoperatively and operated by one single experienced refractive surgeon (RBC), between April 2011 and March Inclusion criteria were aged over 18 years, and stable myopic error less than 8.00 D of MRSE. The exclusion criteria were: history of eye disease and ocular abnormalities that would normally exclude the patient from being a candidate for myopic PRK, previous ocular surgeries, aged over 50 years, less than 470 microns in central corneal pachymetry and preoperative CDVA less than 0.6. Before surgery, all patients had a complete ophthalmic examination, which included: manifest and cycloplegic refractions, keratometry, corneal topography (Orbscan II, Bausch&Lomb, Rochester, NY, USA), ultrasound corneal pachymetry, slitlamp microscopy, applanation tonometry and binocular indirect ophthalmoscopy through a dilated pupil. The surgical technique has been extensively described by the authors elsewhere (Figure 1) 3. Photoablation was performed using the Technolas 217 Z100 (Bausch&Lomb, Rochester, NY, USA) excimer laser platform using our standard nomogram. Following laser ablation, 0.02% mitomycin C (MMC) was applied on the ablated stroma. The duration of MMC application was 12 seconds when the depth of central ablation was less than 65 microns, and 20 seconds if more than 65 microns. Eyes were then thoroughly irrigated with 50 ml of chilled balanced salt solution and a silicon hydrogel contact lens (Acuvue Oasys, Johnson&Johnson Vision Care, Inc) was placed over the cornea until complete re-epithelialization. Our usual postoperative topical and oral analgesic regime was applied in all patients 3. RESULTS Of the 144 patients, 80 were women and 64 men. The mean age (± standard deviation [SD]) was ± 7.09 years (range 18 to 49). Pre-operatively, the mean manifest refraction spherical equivalent (MRSE) was 3.73 ± 1.49 D (range 1 to 7.12 D), mean refractive cylinder 0.65 ± 0.71D (range 0 to 4 D) and mean decimal best spectacle corrected distance visual acuity (CDVA) 0.98 ± Postoperatively, after a minimum of 6 months follow-up (mean 185 ± 17 days), the mean decimal uncorrected distance visual acuity (UDVA) was 0.97 ± 0.08 and MRSE was 0.04 ± 0.33 (range to 0.82) (Table 1); 6 months postoperatively, 96% of eyes had an MRSE within ± 0.50 D, and 99% were within ± 1.00 D of emmetropia (Figure 2).The Efficacy Index (mean postoperative UDVA/mean preoperative CDVA) was 0.99 (Figure 3). Only one eye out of 248 (0.4%) required an enhancement procedure at the end of follow-up. Postoperative mean time for complete re-epithelialization and contact lens removal was 5.1 ± 0.4 days, and no patient required more than 14 days of contact lens wear. Eight eyes had transient grade 1 corneal haze. No eye lost 2 or more lines of CDVA, or presented any significant clinical complication; the Safety Index (mean postoperative CDVA/ mean preoperative CDVA) was 1.02 (Figure 4). No patient presented any intraoperative or early postoperative complications, or required any other technique to complete epithelial debridement. The mean time for complete re-epithelialization and contact lens removal was 4.3 ± 0.4 days, and no patient required more than 14 days of contact lens wear. With respect to the refractive results, we did not notice any significant difference compared to our previous epithelial debridement techniques, and no modification in our previous laser nomograms was needed. No eye presented corneal haze higher than grade 1 after 6 months of postoperative follow-up. DISCUSSION Pain, slow vision recovery, myopic regression and haze have been extensively described as the adverse effects related with conventional PRK. As mentioned previously, several modifications of the initial PRK technique have been introduced in order to minimize these drawbacks. These include laser transepithelial debridement, de-epithelialization with diluted alcohol, epithelial mechanical scraping with scalpels or rotating brushes, and later, the epi-lasik technique 4,5,6,7,8. All these techniques have been found to be safe and effective for treating a wide range of myopias and myopic astigmatisms 9. However, comparing the clinical outcomes among them has been difficult due to the variability in the surgical conditions and protocols 10. Controversy remains as regards the advantages and disadvantages of each method, particularly regarding postoperative pain, recovery of visual acuity, subepithelial scar formation, the toxic effect of alcohol, and synergistic effect with MMC 11,12,13. JOURNAL OF EMMETROPIA - VOL 6, JULY-SEPTEMBER

3 PRK FOR MYOPIA WITH A NEW CORNEAL EPITHELIUM DEBRIDEMENT TECHNIQUE 135 Figure 1. Corneal epithelium debridement technique. A) An 8 mm circular Weck-Cel sponge soaked in 20% alcohol solution is positioned over the central corneal surface for 50 seconds. B) If some solution leaks towards the periphery, it is dried with another Weck-Cel spear. C) Epithelial adhesions are released by applying some pressure with circular movements over the central surface of the cornea. D, E and F) Central loosened corneal epithelium is easily lifted off with the same Weck-Cel spear in a circular epitheliorhexis manner. G) The edges of the debrided area can be slightly extended towards the corneal periphery with the Weck-Cel or a blunt spatula before laser photoablation, and the epithelial flap is discarded. JOURNAL OF EMMETROPIA - VOL 6, APRIL-JUNE

4 136 PRK FOR MYOPIA WITH A NEW CORNEAL EPITHELIUM DEBRIDEMENT TECHNIQUE Figure 2. Achieved versus attempted MRSE correction PREOP 0.00% 0.00% 0.01% Efficacy Index: months POSTOP 78.48% 21.02% UDVA CDVA Figure 3. Changes in mean uncorrected and corrected visual acuity. 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Loss 3 or more Changes in decimal lines of CDVA Loss 2 Loss 1 No change Figure 4. Changes in decimal lines of CDVA. 0.04% 0.00% Gain 1 Gain 2 Gain 3 or more Mechanical debridement is straightforward and effective, but Bowman s layer can be damaged, and a more irregular anterior stromal surface and retained islands of residual epithelium have been described. Moreover, the time required for mechanical debridement is longer, and patients generally experience more discomfort. Alcohol-assisted removal is perhaps easier, faster and more comfortable for both the patient and the surgeon 14,15. However, some pressure needs to be applied with the cone over the ocular globe for seconds, and the 20% ethanol solution may sometimes spill towards the periphery of the cornea, particularly after involuntary ocular movements when the patient feels the pressure of the cone. The spilled solution can damage the ocular surface epithelial cells, and often produces pain and significant irritation of the conjunctiva. In t-prk, total epithelial removal using excimer laser is difficult, and in some cases areas of Bowman s membrane can be unintentionally removed. This may lead to underor overcorrections in refractive results 16. The Epi-LASIK technique requires sophisticated surgical material, and complications such as anterior corneal stromal damage or optic neuropathy related to the suction process have been described 17. In the technique described above, we combine the initial chemical effect of the 20% ethanol solution, which loosens the corneal epithelium, with a non-traumatic mechanical effect produced by the circular movement of the cellulose sponge and the later epithelial peeling. This procedure combines the advantages of the two initial techniques while minimizing their adverse effects. The diluted alcohol separates the epithelium and corneal stroma, creating a smooth, regular surface; however, in contrast to the conventional alcoholassisted technique, no pressure needs to be applied to the ocular globe, and no spillage of the solution occurs, thus minimizing patient discomfort and surgical trauma to the ocular surface. The mechanical effect in this technique is produced by a blunt sponge, thus rendering the use of sophisticated or potentially traumatic surgical instruments unnecessary. In our experience, contact with the circular cellulose sponge is required for 50 seconds in order to easily loosen Table 1: Refractive parameters before and after the procedure Manifest refraction spherical equivalent (D) Manifest cylinder (D) Manifest myopic refraction (D) Manifest decimal corrected distance visual acuity (D) Preoperatively 3.73 ± 1.49 ( 7.12 to 1.00) 0.65 ± 0.71 (0.00 to 4.00) 2.97 ± 1.71 ( 6.75 to 0.50) 0.98 ± 0.05 (1.20 to 0.55) Data given as mean ± standard deviation, with range in parentheses Postoperatively 0.04 ± 0.33 (+0.85 to 0.82) 0.35 ± 0.22 (0.00 to 1.00) ± 0.32 (+0.75 to 0.75) 1 ± 0.04 (1.20 to 0.82) JOURNAL OF EMMETROPIA - VOL 6, JULY-SEPTEMBER

5 PRK FOR MYOPIA WITH A NEW CORNEAL EPITHELIUM DEBRIDEMENT TECHNIQUE 137 corneal epithelium. When exposure time is shorter, removal of the epithelium with the Weck-Cel sponge is often incomplete, and the use of other rigid surgical instruments may be required thereafter. No clinical adverse effects have been found with this alcohol solution exposure time, which is longer than that described in previous techniques. In addition, patient tolerance is excellent, as no pressure is applied over the ocular globe. The technique also allows for complete lifting of the epithelial flap, which can be repositioned over the corneal stroma after laser ablation, if the surgeon considers it appropriate. In the current series, early refractive and anatomic results are consistent with those in previous studies that used different epithelial debridement techniques for myopic PRK, showing excellent efficacy, predictability and safety outcomes in eyes with low myopia 18,19,20,21. Although this was a case series without a control group, and a randomized controlled study would have been a better option to compare this epithelium debridement technique with those previously described, this was not the purpose of our study. Since it was first introduced in our clinic in 2011, most of the surgeons in our group have progressively abandoned their previous debridement methods, and have changed to the above-described technique, which has now been very extensively used in surface ablation photorefractive surgery; the authors have also used this manoeuvre for epithelial debridement in other surgical procedures, such as corneal cross-linking or phototherapeutic keratectomy for anterior corneal disorders, without any adverse effects or unexpected corneal reactions. In conclusion, this corneal epithelium debridement technique combining a chemical and blunt mechanical action has proven to be safe and effective when used for myopic PRK. The minimization of the intraoperative ocular surface damage and the reduction in patient discomfort has allowed us to optimize our surgical performance with this refractive procedure. REFERENCES: 1. Pop, M, Payette Y. Photorefractive keratectomy versus laser in situ keratomileusis: a control matched study. Ophthalmology. 2000;107: Hersh PS, Brint SF, Maloney RK, Durrie DS Gordon M, Michelson MA.Photorefractive keratectomy versus laser in situ keratomileusis for moderate to high myopia. A randomized prospective study. Ophthalmology. 1998; 105: Bilbao-Calabuig R, González-López F, Villada-Casaponsa JR. Combined ethanol-assisted and blunt mechanical corneal epithelial peeling technique. J Emmetropia 2014; Melki SA, Azar DT. LASIK complications: etiology, management and prevention. Surv Ophthalmol. 2001;46: Alio JL, Artola A, Claramonte PJ, et al. Complications of Photorefractive keratectomy for myopia: two year follow-up of 3000 cases. 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J Refract Surg. 2012;28: First author: Rafael Bilbao-Calabuig, MD Clínica Baviera Madrid, Spain JOURNAL OF EMMETROPIA - VOL 6, APRIL-JUNE