To the Editor:
Epipolis laser in situ keratomileusis (epi-LASIK) and laser subepithelial keratomileusis (LASEK) combine the advantages of LASIK and photorefractive keratectomy (PRK), allowing faster visual recovery with less postoperative pain.1 Few studies have shown retinal nerve fiber layer changes after LASIK.24 Because epi-LASIK also involves application of a suction ring similar to LASIK, it may predispose the eye to risk of retinal nerve fiber layer damage. The present study was conducted to evaluate and compare the influence of epi-LASIK and alcohol-assisted LASEK on peripapillary retinal nerve fiber layer using optical coherence tomography (OCT).
Ninety-five patients with myopia (up to ?8.00 D) were included. Mean patient age was 21 ?4.3 years. Aside from the routine preoperative work-up, retinal nerve fiber layer measurements were performed using OCT (OCT#3 STRATUS; Zeiss, Jena, Germany).
Epi-LASIK was performed in 41 patients and LASEK in 54 patients. A pre-assembled epi-microkeratome (Epi-K; Moria SA, Antony, France) was used for epiLASIK. Intraocular pressure (IOP) >65 mmHg was induced and the Chiron Technolas Laser 217 C (Bausch & Lomb, Rochester, NY) was used in the PRK mode in both the groups. During epi-LASIK, the suction time varied from 30 seconds to 1 minute.
Measurements of retinal nerve fiber layer thickness were performed on the first postoperative day and at 1 month following surgery. Retinal nerve fiber layer parameters were compared using analysis of variance (ANOVA) for repeated measurements, and if ANOVA was significant, post hoc (Bonferroni) analysis was applied. A comparison of retinal nerve fiber layer thickness at both follow-up examinations was done using the unpaired t test. A P value<.05 was considered significant.
The mean preoperative spherical equivalent refraction was -5.25±2.50 diopters (D) in the epi-LASIK group and -5.12±2.25 D in the LASEK group (P=.48). In the epi-LASIK group, the mean ablation depth was 78±3 7.42 µm, and in the LASEK group, the ablation depth was 76±36.5µm (P=.56). In the epi-LASIK group, the mean preoperative retinal nerve fiber layer thickness was 96.8±5.8 µm and the inferior, superior, temporal, andnasal averages were 128.4±7.4 µm, 121.38?9.4 µm, 60.5±18.0 µm, and 78.5±10.6 µm, respectively. In the LASEK group, the mean preoperative retinal nerve fiber layer thickness was 98.6±4.5 µm and the inferior, superior, temporal, and nasal averages were 128.5±12.2 pm, 124.1±8.3 µm, 65.5±7.2 µm, and 72.7±12.8 µm, respectively. No significant differences were found between any retinal nerve fiber layer thickness parameters amongst the two study groups preoperatively (unpaired t test) or postoperatively (P>.05).
Refractive surgeries with an epithelial flap obviate the flap-related complications of LASIK, especially in deep set eyes, eyes with narrow palpebral fissure, and eyes with flat or steep corneas and the problems of slow visual recovery and corneal haze of PRK. Similar to conventional LASIK, application of a suction ring during epi-LASIK transiently raises the IOP (60 to 80 mmHg). It has been shown that both LASIK and LASEK do not significantly affect the peripapillary retinal nerve fiber layer thickness.5 Our study shows that epi-LASIK and LASEK have no significant effect on retinal nerve fiber layer thickness parameters at 1-month follow-up. However, larger studies with long-term follow-up are needed to further support this finding.
1. Taneri S, Zieske JD, Azar DT. Evolution, techniques, clinical outcomes and pathophysiology of LASEK: Review of the literature. Surv Ophthalmol. 2004;49:576-602.
2. Nevyas JY, Nevyas HJ, Ne vyas -Wallace A. Change in retinal nerve fiber layer thickness after laser in situ keratomileusis. J Cataract Refract Surg. 2002;28:2123-2128.
3. Roberts TV, Lawless MA, Rogers CM, Sutton GL, Domniz Y. The effect of laser assisted in situ keratomileusis on retinal nerve fiber layer measurements obtained with scanning laser polarimetry. J Glaucoma. 2002;11:173-176.
4. Hollo G, Nagy ZZ, Vargha P, Suveges I. Influence of post-LASIK corneal healing on scanning laser polarimetrie measurement of the retinal nerve fibre layer thickness. BrJ Ophthalmol. 2002;86:627-631.
5. Sharma N, Sony P, Gupta A, Vajpayee RB. Effect of laser in situ keratomileusis and laser-assisted subepithelial keratectomy on retinal nerve fiber layer thickness. J Cataract Refract Surg. 2006;32:446-450.