Electrophysiological measures of dysfunction in early-stage diabetic retinopathy: No correlation between cone phototransduction and oscillatory potential abnormalities.

PURPOSE: To define the relationship between abnormalities in the activation phase of cone phototransduction and the oscillatory potentials (OPs) of the light-adapted electroretinogram in diabetics who have mild or no retinopathy.
METHODS: Subjects included 20 non-diabetic controls and 40 type-2 diabetics (20 had no clinically apparent diabetic retinopathy [NDR] and 20 had mild nonproliferative DR). Single flash responses for a series of stimulus retinal illuminances were measured under light-adapted conditions using conventional techniques. The a-waves of the responses were fit with a delayed Gaussian model to derive Rmp3 (maximum amplitude of the massed photoreceptor response) and S (phototransduction sensitivity). OPs were extracted from the responses by conventional band-pass filtering.
RESULTS: Analysis of variance (ANVOA) indicated that both diabetic groups had significant OP amplitude and S reductions compared to the controls, whereas Rmp3 did not differ significantly among the groups. Although log OP amplitude and log Rmp3 were significantly correlated for the control subjects for each flash retinal illuminance (all r > 0.49, p < 0.03), log OP amplitude and log Rmp3 were not correlated for either diabetic group for any flash retinal illuminance (all r ≤ 0.36, p ≥ 0.13). Log OP amplitude and log S were generally not correlated significantly for the control or diabetic groups.
CONCLUSION: OP amplitude losses do not appear to be related to reduced cone sensitivity in early-stage diabetic retinopathy. This suggests that diabetes may separately affect cone function, as evidenced by cone phototransduction sensitivity losses, and inner-retina function, as evidenced by OP amplitude losses.