Studying the factors related to refractive error regression after PRK surgery

Mehdi Naderi,Soheila Khodakarim,Siamak Sabour,Farid Daneshgar

doi:10.1186/s12886-018-0879-y

Abstract

BackgtoundPhotorefractive keratectomy (PRK) is used for a wide range of refractive errors such as low to moderate myopia, hyperopia and astigmatism. While many improvements have been made in laser application and accuracy as well as the modes of corneal flap removal, and although the results are somewhat predictable, regression of refractive errors is still a common complaint among the patients undergoing refractive surgery with Excimer Laser. We aimed to determine related factors of regression following photorefractive keratectomy (PRK) in different types of refractive errors.MethodsThis cross-sectional study included patients who had undergone PRK more than 6 months previously and investigated refractive error regression and related factors. The participants were those who had PRK eye surgery for the first time from 2013 to 2016 using Technolas 217z100. A refraction value of spherical equivalent > 0.75 D after cycloplegic refraction was defined as refractive error regression.ResultsA total of 293 eyes on 150 subjects were studied. The preoperative refractive error of the eyes were as follows: 5.5% were myopic, 1% were hyperopic, 4.8% had astigmatism, 76% had myopic astigmatism and 12.6% had hyperopic astigmatism. Regressed and non-regressed eyes were assessed using the generalized estimating equations for the probabilistic variables of demographic characteristics, topography and eye refraction. The variables of simulated keratometry astigmatism (simK) (OR = 2.8; p = 0.04), 5 mm irregularity (OR = 3.56; p = 0.01) and sphere value (OR = 1.98; p = 0.01) were significantly related to refractive error regression. There was no significant relationship between the regressed and non-regressed eyes of the same person (p ≥ 0.05).ConclusionThere was a positive relationship between the increase of 5 mm irregularity, simK, sphere value before surgery and refractive error regression. Age, sex and type of refraction error of the patient and the expertise of the PRK surgeon could change the general results; therefore, not all cases should be dealt with identically.

Highlights

Current advances in refractive surgery have caused dramatic changes in ophthalmology
The current study found a relationship between simulated keratometry astigmatism (simK) and 5 mm irregularity and refractive error regression after photorefractive keratectomy (PRK)
The current study showed that, in general, a relationship exists between the variables of 5 mm irregularity, simK and sphere value before surgery and the regression of refractive error; the variables of age, sex and type of refractive error and surgeon specialty could change the general results

Summary

Introduction

Current advances in refractive surgery have caused dramatic changes in ophthalmology. PRK is used for a range of refractive errors, including low to moderate myopia, hyperopia and astigmatism [2, 3]. While many improvements have been made in laser applications and accuracy as well as the mode of corneal flap removal, The factors associated with the need for retreatment after LASIK surgery include a small optical zone [10,11,12], flap thickness [13], high correction [14], keratometry readings [15], significant astigmatism [6, 10, 16], age over 40 years [16]. In PRK, they include the use of Mitomycin [17], refractive correction > − 5.00 D, smaller optical zone (< 6.00 mm) and unstable fixation during. Determining the factors associated with regression in PRK surgery can help select the best case for this type of surgery and reduce the financial burden of the patient

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