Changes in Corneal Biomechanical Properties after Laser-Assisted in situ Keratomileusis and Photorefractive Keratectomy in Myopia

OBJECTIVE: To compare changes in corneal biomechanical properties after laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) in low and moderate myopia by Ocular Response Analyzer. STUDY DESIGN: Quasi-experimental study. Place and Duration of the Study: Armed Forces Institute of Ophthalmology (AFIO), Rawalpindi, Pakistan, between September 2020 and April 2022. METHODOLOGY: Myopic correction was done in forty-six eyes of twenty-three patients by PRK, and forty-seven eyes of twenty-four patients by LASIK. Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured using Ocular Response Analyzer (ORA), pre-operatively, and then 1, 3, and 6 months, postoperatively. The relationship between the amount of myopia treated and biomechanical properties was also studied. RESULTS: CRF and CH were decreased significantly after LASIK and PRK. A significantly larger decrease in CRF was observed after LASIK as compared to PRK at 6 months (Mann-Whitney U test: CRF, p = 0.02); however, decrease in CH was not statistically significant between LASIK and PRK at 6 months period (Mann-Whitney U test: CH, p = 0.388). A significant correlation was observed between the changes in biomechanical properties and extent of myopic correction after LASIK and PRK. CONCLUSION: Biomechanical strength of the cornea was significantly reduced by PRK and LASIK, which was also dependent on the spherical equivalent (SEQ) of myopic correction. A significantly larger change in CRF was observed after LASIK as compared to post PRK. KEY WORDS: Myopia, Laser in situ keratomileusis, Photorefractive keratectomy, Cornea, Biomechanics.