PURPOSE: To evaluate the correlation between improvement in visual acuity and the reduction of foveal thickness after a single intravitreal injection of 4 mg of triamcinolone in diabetic macular edema. DESIGN: Prospective, interventional, nonrandomized clinical trial. METHOD: PATIENTS: In a prospective study 24 eyes with diabetic macular edema were treated with an intravitreal injection of 4 mg of triamcinolone acetonide. MAIN OUTCOME MEASURES: Best,corrected logMAR visual acuity and optical coherence tomography were performed at baseline and 3 months after the treatment. RESULTS: At baseline the average foveal thickness was 462 +/- 154 mu m (95% confidence interval, 397-527 mu m) and at 3 months 257 +/- 114 mu m (95% confidence interval, 209-305 mu m) (P < .0001). The best-corrected logMAR average visual acuity was 60.5 +/- 10.5 (95% confidence interval, 56.0-65.0) ETDRS letters at base, line compared with 65.5 +/- 11.1 (95% confidence interval, 60.8-70.1) 3 months after the injection (P = .0001). There was no correlation between the improvement in visual acuity and the reduction of foveal thickness (r = 0.054, P = .8), but there was a correlation between reduction in foveal thickness and the age of the patients (r = 0.53, P = .008). CONCLUSION: A single injection of 4 mg of intravitreal triamcinolone acetonide effectively reduces the foveal thickness in diabetic macular edema and improves visual acuity, but there does not appear to be a strong correlation between the reduction of foveal thickness and the improvement in visual acuity. (c) 2005 by Elsevier Inc. All rights reserved.