The nature and extent of retinal dysfunction associated with diabetic macular edema

To evaluate the nature and extent of retinal dysfunction in the macular and surrounding areas that occurs in patients with diabetes with clinically significant macular edema (CSME).

Eleven patients were evaluated before focal laser treatment. Multifocal electroretinogram (ERG) and full-field ERG techniques were used to assess the effects of diabetic retinopathy and CSME on macular, paramacular, and peripheral retinal function. A modified visual field technique was used to obtain local threshold fields. The relationship between local sensitivity changes and local ERG changes was determined.

Local ERG responses were significantly delayed and decreased in amplitude, and timing changes were observed in a larger area of the retina than amplitude changes. Visual field deficits were similarly widespread with marked sensitivity losses occurring in retinal areas with normal ERG amplitudes and in areas that appeared to be free of fundus abnormalities. Despite this similarity and the finding that retinal areas with elevated thresholds have timing delays, timing delays were not good predictors of the degree of threshold elevation.

The results demonstrate the widespread nature of timing deficits and visual field deficits that are associated with CSME.