PURPOSE: To evaluate the retinal thickness analyzer, a new image analyzer involving laser-slit biomicroscopy, for quantitative assessment of retinal thickness in patients with macular edema secondary to retinal vein occlusion. METHODS: Fifty eight patients (central retinal vein occlusion, 22 eyes; branch retinal vein occlusion, 36 eyes) with a clinical diagnosis of macular edema associated with retinal vein occlusion were evaluated. Retinal thickness analysis was performed with the retinal thickness analyzer. A green helium-neon laser slit directed into the eye was scanned to generate optical cross-sections of the retina. Images were analyzed by an automated software algorithm, and a detailed map of the retinal thickness was obtained. RESULTS: Laser slit images obtained with the retinal thickness analyzer in patients with macular edema associated with retinal vein occlusion dis closed intraretinal changes such as retinal edema, cystoid spaces, and hemorrhages. Linear regression analysis showed a significant relationship between the macular thickness in the central fovea and corrected visual acuity reported on a logMAR scale (P = .002, adjusted R-2 = 0.40 in central retinal vein occlusion; P = .002, adjusted R-2 = 0.34 in branch retinal vein occlusion). CONCLUSION: We confirmed the capability of the retinal thickness analyzer to provide rapid and precise evaluation of macular thickening in patients with retinal vein occlusion. (C) 1998 by Elsevier Science Inc. All rights reserved.