Comparison of Intraocular Pressure before and after Laser in Situ Keratomileusis Measured with Applanation Tonometry, Non Contact Tonometry and Rebound Tonometry

Abstract

Background Measurement of intraocular pressure (IOP) plays a central role throughout ophthalmology. It is part of routine ophthalmologic examinations and important in the management and follow-up of patients with glaucoma. While elevated IOP remains the most important risk factor for development and progression of open angle glaucoma, at least half of the population diagnosed with open angle glaucoma is asymptomatic. Objectives The aim of our study is to compare the accuracy of intraocular pressure measurement before and after Laser in situ keratomeulsis (LASIK) surgery using three different types of Tonometers: Goldmann Applanation tonometry (GAT), Non contact tonometry (NCT) and Rebound tonometry (I care), considering the change in the central corneal thickness (CCT). Patients and Methods In this study Eighty eyes of 40 patients with mean age of 27.00±6.00 years were scheduled for LASIK..Central corneal thickness before and after surgery was obtained by Ultrasound (US) pachymetry.IOP values were measured before and after surgery using three different types of Tonometers: Goldmann Applanation tonometry, Non contact tonometry and Rebound tonometry. Results The results revealed that lower post-operative IOP measurements using all techniques. The least affected technique was Non –contact with IOP change 16%, followed by GAT with IOP change 18%, and finally Rebound with IOP change 19 %, respectively. The percentage of change in CCT between pre- and post- LASIK surgery measured with the Ultrasound pachymetry was statistically highly significant. There was a clinical significant correlation between Percentage of tissue ablation (PTA) and IOP change for GAT, NCT and rebound tonometry. Also, there was a significant correlation between Residual stromal bed (RSB) and IOP change for GAT and NCT. There was no clinical significant correlation between Ablation depth (AD) and percentage of change of IOP measurements pre and post LASIK, except for IOP measured with GAT when AD < 40.00 µm. Conclusion Refractive surgery causes significant lowering of IOP as measured using Goldmann applanation tonometry, non contact tonometry and rebound tonometry. The least affected tonometry post LASIK is non contact tonometry. The reduction was correlated to the percentage of tissue ablated. The ideal method to measure IOP in post-LASIK patients would be a device that is free of corneal factors.