Retinal function in normal and diabetic eyes mapped with the slow flash multifocal electroretinogram.

PURPOSE: It has been suggested that late components of the standard multifocal electroretinogram (mfERG) are preferentially affected by diabetes mellitus. The slow-flash (sf-)mfERG stimulates with flashes separated by dark periods, facilitating interpretation of late first-order response components compared with standard multifocal stimulation. Retinal function and response component changes were examined using the sf-mfERG in diabetic subjects with and without diabetic retinopathy.
METHODS: Eighteen control subjects, 12 diabetic patients without retinopathy and 17 diabetic patients with nonproliferative diabetic retinopathy (NPDR), were tested monocularly. A total of 103 areas of the central 45 degrees were stimulated by pseudorandom 100-cd/m2 flashes separated by at least 53.3 ms. Major components and the amplitude of the first-order sf-mfERGs were examined. Each subject's N1, P1, and N2 implicit times (ITs) and scalar product amplitudes (SPs) were measured at all 103 retinal locations and converted into z-scores based on the control values. Abnormalities were defined as z-scores greater than 2.33 (P < 0.01).
RESULTS: Local functional abnormalities were found in both the diabetic patients with NPDR and in those without retinal disease. In both groups of diabetic patients, most abnormalities occurred more frequently in the inferior retina. Later components (P1 and N2) of the local sf-mfERGs were not preferentially affected by diabetes. The local SP and P1 IT measures distinguished the subject groups better than N1 IT and N2 IT.
CONCLUSIONS: Local functional retinal abnormalities in diabetic persons with or without NPDR can be detected and mapped by the sf-mfERG. Diabetes and NPDR do not, however, preferentially affect the late P1 and N2 response components.