Multifocal Electroretinogram (mfERG) Delays Identify Sites of Subsequent Diabetic Retinopathy

Abstract

Abstract: : Purpose: To examine the potential of abnormal mfERGs to predict the development of diabetic retinopathy at corresponding retinal locations one year later. Methods: 9 eyes of 9 diabetics with non-proliferative diabetic retinopathy (NPDR) and 9 eyes of 9 diabetics without retinopathy were re-tested 12 months (T1) after initial testing (T0). MfERGs were recorded from the central 45 degrees using standard conditions, and fundus photos were taken within 2 months of each recording. Using a "stretching" method (Hood & Li, 1997), mfERG amplitudes (AMP) and implicit times (IT) were derived at the 103 stimulated retinal locations and a Z-score for each measure was calculated based on results obtained from 20 age-matched controls. MfERG abnormalities were defined as Z-scores >= 2 for ITs and <= -2 for AMPs. A template was used to map local retinopathy identified on fundus photos onto mfERG Z-scores. MfERGs corresponding to pathology and their immediate neighbors were grouped as "retinopathy areas". The relationship between abnormal Z-scores at T0 and new retinopathy areas at T1 was examined. Results: 5 of the 18 eyes developed new retinopathy after 1 year. In these eyes, 80.2% of the mfERGs (73 out of 91) in areas that developed new retinopathy had abnormal ITs at T0. In contrast, only 24% of the responses (74 out of 304) in regions that remained retinopathy-free were abnormal at T0. The frequency of AMP abnormalities at T0 was low and did not differ for areas that did or did not develop retinopathy (4.4% vs. 3.0% abnormal Z scores). No eyes without retinopathy at T0 developed new retinopathy within the one-year study period, although some had abnormal ITs and/or AMPs at T0. The frequency of IT abnormalities did not change in these subjects over time (19% abnormal mfERG responses at T0 vs. 17% at T1). However, there was a decrease in AMP (24% abnormal mfERG at T0 vs. 44% at T1). Conclusions: Localized functional abnormalities of the retina reflected by mfERG delays often precede diabetic retinopathy. Those functional abnormalities appear to predict the specific sites of new retinopathy observed one year later. New retinopathy might be more likely to develop in eyes with NPDR than diabetic eyes without retinopathy.

Keywords: diabetic retinopathy • electroretinography: clinical