Intraocular Pressure Changes in Myopic Patients Undergoing Laser In-Situ Keratomileusis and Photorefractive Keratectomy.

OBJECTIVE: To assess the variation in intraocular pressure measurements between Ocular Response Analyzer (ORA) and Goldmann Applanation Tonometer (GAT) in myopic patients undergoing laser assisted in-situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). STUDY DESIGN: Quasi-experimental study. Place and Duration of the Study: Armed Forces Institute of Ophthalmology (AFIO), National University of Medical Sciences, Rawalpindi, Pakistan, between September 2020 and 2021. METHODOLOGY: Myopic patients undergoing LASIK and PRK during the study period were selected. Baseline examinations and postoperative follow-ups were carried out to measure intraocular pressure at 1, 3, and 6 months after LASIK or PRK, using Goldmann Applanation Tonometer (GAT) and Ocular Response Analyzer, corneal compensated IOP (ORA IOPcc). RESULTS: One hundred and thirteen eyes underwent myopic refractive surgery, LASIK (n = 60) or PRK (n = 53). Mean age of patients was 23.6 ± 4.11 years in the PRK group and 24.4 ± 5.94 years in LASIK group. For the PKR group, the GAT IOP value increased at 1-month (p <0.001), decreased at 3-month (p <0.001) and further decreased at 6-month (p <0.001) follow-up postoperatively. In the LASIK group, the GAT IOP value decreased at all time points (p <0.001). In both groups, the mean ORA IOPcc value increased at 1 month (p <0.001), decreased at 3-month (p <0.001) and further decreased at 6-month (p <0.001) follow-up postoperatively. The IOP mean values were generally found to be higher when measured using ORA as compared with GAT. CONCLUSION: Corneal refractive surgery markedly decreased IOP. This decrease in IOP was observed more after LASIK than after PRK. ORA was less likely to underestimate the intraocular pressure than GAT. KEY WORDS: Myopia, Laser in-situ keratomileusis, Photorefractive keratectomy, Tonometery ocular, Intraocular pressure.

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.