Rod function in diabetic patients without and with early diabetic retinopathy

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.

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).

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).

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.