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 year s) and 19 approximately age-matched healthy volunteers underwent multi focal ERG testing. One hundred three retinal locations within the cent ral 50 degrees were stimulated concurrently, according to a pseudorand om m-sequence. Response components were extracted for each stimulated retinal location. Results. In diabetic patients with recinopathy, the overall amplitudes were reduced (P < 0.01), and peak implicit times we re increased (P < 0.01) in the first-order component (mean flash respo nse) and in the first slice of the second-order component (local two f lash interaction). In addition, local reductions of amplitude could be seen in the first-and second-order components. In patients without re tinopathy, only amplitudes of the second-order component were reduced (P < 0.01). Another salient difference was observed in a special featu re of the second-order component that was reduced in diabetic patients , with and without retinopathy (P < 0.05). Conclusions, Second-order c omponents depend on nonlinear dynamics. Thus our findings indicate cha nges in the nonlinear dynamics of a fast-gain control in diabetic pati ents, presum ably located in the inner retina. This suggests that earl y functional changes of the inner retina are evident in diabetic patie nts before impairment of the outer retina is observed, Multifocal nonl inear analysis permits the detection of subclinical diabetic retinopat hy and offers the advantage of topographic mapping of retinal dysfunct ion.