Retinal thickness change after focal laser treatment of diabetic macular oedema

Laser photocoagulation has been used successfully for the treatment of clinically significant macular oedema to reduce the risk of loss of vision in diabetic patients. A quantitative method for measuring retinal thickness was applied to 20 patients with diabetic macular oedema before and 4 months after focal laser treatment to assess the reduction in retinal thickening and its relation to visual acuity. The degree of thickening at each location, defined by thickness index, was determined relative to the corresponding average value in normal subjects. Comparison of quantitative retinal thickness measurements before and after treatment demonstrated that treatment at thickness indices of approximately 1.6 (60% thickening) has nearly 50% probability for reversal of thickening to within the normal range (< or = 1.3), whereas at thickness indices greater than 2.8 (180% thickening) there is less than 2.5% probability that reversal will occur. The level of foveal thickening before treatment strongly correlated with the degree of thickening after treatment. Most of the eyes with an improvement in visual acuity had a foveal thickness within the normal range at 4 months' follow up. These findings suggest that quantitative retinal thickness measurement provides an objective assessment of the degree of macular oedema and can be useful for monitoring the efficacy of focal laser treatment in reducing the thickening and relating the latter to visual outcome.