Relationship between optical coherence tomography-measured central retinal thickness and visual acuity in diabetic macular edema

Objective: To compare optical coherence tomography (OCT)-measured retinal thickness and visual acuity in eyes with diabetic macular edema (DME) both before and after macular laser photocoagulation. Design: Cross-sectional and longitudinal study. Participants: Two hundred ten patients (251 eyes) with DME enrolled in a randomized clinical trial of laser techniques. Methods: Retinal thickness was measured with OCT and visual acuity was measured with the electronic Early Treatment of Diabetic Retinopathy procedure. Main Outcome Measures. Optical coherence tomography-measured center point thickness and visual acuity. Results: The correlation coefficients for visual acuity versus OCT center point thickness were 0.52 at baseline and 0.49, 0.36, and 0.38 at 3.5, 8, and 12 months after laser photocoagulation. The slope of the best fit line to the baseline data was approximately 4.4 letters (95% confidence interval, 3.5-5.3) of better of visual acuity for every 100-mu m decrease in center point thickness at baseline with no important difference at follow-up visits. Approximately one third of the variation in visual acuity could be predicted by a linear regression model that incorporated OCT center point thickness, age, hemoglobin A1C, and severity of fluorescein leakage. The correlation between change in visual acuity and change in OCT center point thickening 3.5 months after laser treatment was 0.44, with no important difference at the other follow-up times. A subset of eyes showed paradoxical improvements in visual acuity with increased center point thickening (7%-17% at the 3 time points) or paradoxical worsening of visual acuity with a decrease in center point thickening (18%-26% at the 3 time points). Conclusions: There is modest correlation between OCT-measured center point thickness and visual acuity, and modest correlation of changes in retinal thickening and visual acuity after focal laser treatment for DME. However, a wide range of visual acuity may be observed for a given degree of retinal edema. Thus, although OCT measurements of retinal thickness represent an important tool in clinical evaluation, they cannot substitute reliably as a surrogate for visual acuity at a given point in time. This study does not address whether short-term changes on OCT are predictive of long-term effects on visual acuity.