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TM McCarty, DR Hardten, NJ Anderson, TW Samuelson; Assessment of Optic Nerve Parameters After Laser In-Situ Keratomileusis (Lasik) With and Without the Use of Brimonidine . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2094.
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Purpose: To determine the effect of LASIK on optic nerve parameters structurally and functionally, and to evaluate the effects of perioperative treatment with brimonidine. Methods: Fifty-one patients scheduled for routine, bilateral, myopic LASIK surgery were randomized in a prospective double masked fashion to receive brimonidine in one eye and placebo in their fellow eye. The study drug was used tid for three days prior to surgery, once at the end of the procedure, and tid for three weeks following surgery. Patients were evaluated pre-operatively, at 1-day, 1-month, and 3-months following LASIK. Primary outcome variables included; visual acuity, nerve fiber layer analysis, automated visual field and other psychophysical tests. Results: Brimonidine did not change the outcome of any of the parameters analyzed in this study. At three months post-op the mean spherical equivalent refractive error was +0.04 D in the brimonidine group and +0.01 D in the placebo group. There was not a statistically significant change in any of the visual field parameters measured in either the placebo or brimonidine group post-operatively. However, both the placebo and brimonidine group did show a statistically significant change in many of the direct GDx measures such as average thickness, ellipse and superior average; these were generally reduced in both groups. Conversely, there was no statistically significant change in GDx parameters following LASIK in either group in the measures of symmetry, or ratio measures such as superior ratio, inferior ratio, or superior/nasal ratio. Conclusion: LASIK with or without brimonidine did not affect the structure or function of the optic nerve parameters studied. Direct GDx measures were globally reduced following myopic LASIK, however, the ratio measures were generally unaffected. The reduction in direct, quantitative measures is consistent with previous studies that have suggested that such change represents alteration in corneal birefringence following excimer laser ablation. The lack of change in symmetry and ratio measures is not unexpected, as corneal birefringence induced would be equally distributed to the various ellipse segments.
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