Evaluation of neuroprotective qualities of brimonidine during LASIK

Abstract

Purpose: The effects of LASIK-induced increased intraocular pressure on the optic nerve and nerve fiber layer are poorly understood. This study evaluates the effect of LASIK on several optic nerve parameters, both structural (scanning laser polarimetry) and functional (automated perimetry). In addition, the potential neuroprotective effect of perioperative brimonidine is studied.

Design: Randomized self-controlled, masked trial.

Participants: Fifty-one patients scheduled for routine, bilateral, myopic LASIK. Patients served as their own control and received brimonidine in one eye and placebo in their fellow eye.

Methods: Patients were treated with the VISX Star S3 Excimer Laser. Patients were evaluated preoperatively and at 1 day, 1 month, and 3 months after LASIK. Topical brimonidine or control vehicle was administrated three times daily for 3 days before surgery. In addition, 1 drop of the respective study drug was instilled at the end of the procedure, and the patient continued the study drug three times daily for 3 weeks after surgery in the respective (randomized) eye.

Main outcome measures: Visual acuity, nerve fiber layer analysis, automated visual field, contrast sensitivity, color vision, and pupillary function.

Results: Brimonidine did not change the outcome of any of the parameters analyzed in this study. There was not a statistically significant change in any of the visual field parameters (mean elevation or depression, pattern standard deviation, and corrected pattern standard deviation) measured in either the placebo or brimonidine group postoperatively. However, both the placebo and brimonidine group did show a statistically significant change in many of the direct Nerve Fiber Analyzer GDx (NFA GDx) measures. The average thickness, ellipse, and superior average were generally reduced in both groups. There was, however, no statistically significant change after LASIK in either group in indirect NFA GDx parameters such as symmetry, superior ratio, inferior ratio, or superior/nasal ratio. There was no significant change in optic nerve appearance, contrast sensitivity, or color vision between treatment groups before or after LASIK.

Conclusions: LASIK with or without brimonidine did not affect the structure or function of the parameters of the optic nerve studied. Direct NFA GDx measures were globally reduced after myopic LASIK; however, the ratio measures were generally unaffected. The reduction in direct, retinal nerve fiber layer measures, in the absence of change in ratio measures and other optic nerve parameters and absence of brimonidine effect, suggest an alteration in corneal birefringence after excimer laser ablation.