Structural and Functional Abnormalities in Early-stage Diabetic Retinopathy.

Purpose: To evaluate the relationship between microperimetric (MP) sensitivity and retinal thickness measured at co-registered retinal locations in individuals who have mild or no diabetic retinopathy.

Methods: Fifty non-diabetic control subjects and 50 type-2 diabetic subjects participated (25 had no clinically apparent DR [NDR] and 25 had mild nonproliferative DR [MDR]). MP sensitivity was measured at 36 retinal locations that were arranged in three concentric rings centered on the fovea (radii of 3°, 6°, and 12°). Optical coherence tomography (OCT) images were obtained, and total retinal thickness (TRT), inner retinal thickness (IRT), and outer retinal thickness (ORT) were quantified from the OCT images at locations that matched the MP measures. Linear quantile mixed models (LQMMs) and linear quantile models (LQMs) were used to compare MP and thickness values for the three subject groups and to quantify structure-function relationships.

Results: The statistical models indicated significant TRT and IRT reductions in the NDR and MDR groups, relative to the controls, that were most apparent in the 3° ring. By contrast, ORT was not reduced significantly for either diabetic group. MP sensitivity was reduced significantly within each ring and for both diabetic groups. Despite reductions in both thickness and sensitivity, the structure-function associations were generally weak with borderline statistical significance. For example, a TRT or IRT reduction of approximately 27 µm was predicted to result in approximately 1 dB of MP sensitivity loss for the MDR group ( = .03 and 0.05, respectively).

Conclusions: The results support previous findings of early retinal neurodegeneration in diabetics who have NDR or MDR. Interestingly, the structural and functional deficits appear to be only weakly associated, suggesting that mechanisms in addition to retinal thinning underlie the functional defects in early-stage DR.