Rod function in diabetic patients without and with early diabetic retinopathy.

Purpose: To compare rod function among diabetic patients without and with mild nonproliferative diabetic retinopathy (DR) and healthy controls by means of scotopic microperimetry and dark-adapted electroretinography.
Methods: Sixty-one diabetic patients and 30 age-matched controls (control group) underwent complete ophthalmic examination, scotopic microperimetry, and dark-adapted 0.01 electroretinography (DA-ERG).
Results: In 32 eyes, DR was absent (no-DR group); in 29 eyes, only microaneurysms were observed (DR group). No statistically significant differences in fixation stability, fixation location, or scotopic sensitivity among the 3 groups were observed. Implicit time and amplitude of the DA-ERG b-wave of no-DR and DR groups were not different from controls. Scotopic microperimetry showed a dense scotoma centered onto the fovea in all subjects, consistent with the rod-free zone. Greater scotopic sensitivity was found in a ring located 8° from the fovea (9.33 ± 1.33 dB).
Conclusions: Diabetic patients without DR and with mild nonproliferative DR did not show alterations in rod-based function, as examined by microperimetry and confirmed by DA-ERG. Scotopic microperimetry measures rod-based function and offers additional information in the evaluation of the aspects of involvement of retinal cells in diabetes.