EFFECT OF SURGERY ON VISUAL-FIELD PROGRESSION IN NORMAL-TENSION GLAUCOMA

Purpose: The effect of intraocular pressure-lowering surgery on the ra te of visual field progression in normal-tension glaucoma (NTG) was st udied. Methods: Seventeen patients with NTG who underwent trabeculecto my in one eye for worsening visual field loss were included in the fir st part of the study. All patients had Humphrey 24-2 visual fields at the rate of 2-3 fields per year. Pointwise linear regression analysis of the visual field data was done separately for the preoperative and postoperative periods. This was performed for both operated and fellow eyes. The mean slope (MS), which indicates rate of visual field progr ession, was calculated. Change in MS was correlated with change in int raocular pressure (IOP). For the second part of the study, 11 patients who had a minimum of 4 visual fields and 18 months of follow-up befor e surgery were identified. Using the preoperative fields, the rate of sensitivity loss for each visual field location in the operated eye wa s ascertained for every patient. This rate of loss was extrapolated to generate the expected visual fields, assuming an unchanged rate of pr ogression. The mean sensitivity of the expected visual field was compa red with that of the actual field at the last follow-up. Results: The MS in the operated eyes improved from -2.97 +/- 3.21 (mean +/- SD) in the preoperative period to 0.53 +/- 3.83 (P < 0.005; Student's t test) postoperatively. In the fellow eyes the MS changed from -1.78 +/- 2.5 5 to -1.43 +/- 3.01 (P = 0.754). There was a weak correlation between change in MS and percentage IOP decrease (correlation coefficient 0.39 ). The difference in mean sensitivity between the expected and actual visual fields was -3.72 dB (P = 0.002), and was better in the actual f ield. Conclusions: In this study, surgical lowering of IOP resulted in a slower rate of visual field loss in the operated eye.