Abstract
Purpose: :
The implicit time of the multifocal electroretinogram (mfERG) has been shown to be delayed in retinal locations that have or will subsequently develop fundus signs of diabetic retinopathy. The goal of this study was to characterize, over a two year period, the spatial and temporal relationships between local changes in retinopathy status and changes in retinal function as evidenced by mfERG implicit time in the eyes of diabetic subjects with some, predominantly mild, baseline nonproliferative diabetic retinopathy (NPDR).
Methods: :
mfERGs and 50 deg fundus photos were obtained at baseline (T0) and at two annual follow–ups (T1 and T2) from 10 diabetic subjects with some T0 NPDR. The photos were graded blind to the mfERG results and the locations of retinopathy were mapped onto the mfERG measurements. Twenty–five age–similar normal subjects served as controls. mfERG implicit times were measured at each of the 103 test locations using a template stretching method (Hood & Li, 1997) and Z–scores were calculated based on the control data. The tested retinal area was divided into 35 contiguous zones. Each zone was assigned its retinopathy status and the maximum implicit time Z–score within it. Z–scores > 2 were classified as abnormal.
Results: :
At T0, 42 of the 350 total zones (12%) in the diabetic eyes had retinopathy, and the presence of retinopathy was associated with abnormal implicit times (P < 0.001). At T1, 24 of 308 zones (8%) developed new retinopathy, and retinopathy development was also associated with abnormal T0 implicit times (P < 0.001). Implicit times became marginally more abnormal over time in zones where retinopathy persisted from T0 to T2 (P < 0.04). Nineteen of the 42 zones (45%) with T0 retinopathy had resolution of fundus signs at T1; this resolution was not associated with improved implicit times at either T1 or T2 (P > 0.20).
Conclusions: :
These results indicate that local functional abnormalities exist before and after the appearance of spatially–associated diabetic retinopathy. Furthermore, they indicate that resolution of early retinopathy signs is not associated with improvement in retinal function. The mfERG implicit time provides a picture of diabetic retinal dysfunction that is not seen in fundus signs of retinopathy.
Keywords: electroretinography: clinical • diabetic retinopathy • diabetes