Mapping of retinal function in diabetic retinopathy using the multifocal electroretinogram.

PURPOSE To investigate focal abnormalities in the electroretinogram (ERG) signal in diabetic patients, with and without retinopathy, using a multifocal ERG. METHODS Sixteen patients with diabetes mellitus, 8 of whom had diabetic retinopathy (mean duration of diabetes: 18.5 years) and 19 approximately age-matched healthy volunteers underwent multifocal ERG testing. One hundred three retinal locations within the central 50 degrees were stimulated concurrently, according to a pseudorandom m-sequence. Response components were extracted for each stimulated retinal location. RESULTS In diabetic patients with retinopathy, the overall amplitudes were reduced (P < 0.01), and peak implicit times were increased (P < 0.01) in the first-order component (mean flash response) and in the first slice of the second-order component (local two flash interaction). In addition, local reductions of amplitude could be seen in the first- and second-order components. In patients without retinopathy, only amplitudes of the second-order component were reduced (P < 0.01). Another salient difference was observed in a special feature of the second-order component that was reduced in diabetic patients, with and without retinopathy (P < 0.05). CONCLUSIONS Second-order components depend on nonlinear dynamics. Thus our findings indicate changes in the nonlinear dynamics of a fast-gain control in diabetic patients, presumably located in the inner retina. This suggests that early functional changes of the inner retina are evident in diabetic patients before impairment of the outer retina is observed. Multifocal nonlinear analysis permits the detection of subclinical diabetic retinopathy and offers the advantage of topographic mapping of retinal dysfunction.