Reduced Contrast Sensitivity is Associated With Elevated Equivalent Intrinsic Noise in Type 2 Diabetics Who Have Mild or No Retinopathy

PURPOSE: To evaluate explanations for contrast sensitivity (CS) losses in subjects who have mild nonproliferative diabetic retinopathy (NPDR) or no diabetic retinopathy (NDR) by measuring and modeling CS in luminance noise. METHODS: Ten diabetic subjects with NDR, 10 with mild NPDR, and 10 age-equivalent nondiabetic controls participated. Contrast threshold energy (E(t)) was measured for letters presented in the absence of noise (E(t0)) and in four levels of luminance noise. Data were fit with the linear amplifier model to estimate inferred noise level within the visual pathway (N(eq)) and sampling efficiency (ability to use stimulus information optimally). E(t0), N(eq), and efficiency were compared to clinical characteristics. RESULTS: N(eq) was correlated with E(t0) for the diabetic subjects (r = 0.93, P < 0.001) and ranged from normal to 12-times the upper limit of normal. ANOVA indicated significant differences among the subject groups for E(t0) and N(eq) (both F > 11.92, P < 0.001). E(t0) and N(eq) were elevated for the mild NPDR group compared to the control and NDR groups (all t > 3.89, P ≤ 0.001); the NDR and control groups did not differ significantly (all t < 0.61, P > 0.55). There were no significant efficiency differences among the groups (F = 1.29, P = 0.29). N(eq) was correlated significantly with disease duration, microperimetric sensitivity, and Pelli-Robson CS. CONCLUSIONS: Elevated contrast threshold may be associated with increased intrinsic noise in early-stage diabetic subjects. Results suggest that noise-based CS measurements can provide important information about early neural dysfunction in these individuals.