The scotopic threshold response in diabetic retinopathy.

The scotopic threshold response (STR) is a recently discovered component of the electroretinogram. It is a corneal negative deflection elicited in the fully dark adapted eye to dim stimuli, and appears to originate in the inner retina. The STR was recorded in a group of 50 insulin dependent diabetics with various degrees of diabetic retinopathy, who had not undergone laser photocoagulation. In addition, the scotopic b-wave, oscillatory potentials (OPs) and a pattern electroretinogram (PERG) were recorded. Retinopathy was assessed with stereo colour photographs of the seven standard fields as defined in the Diabetic Retinopathy Study. Retinopathy level was assigned to each eye using a modification of the Airlie House Classification System. Fluorescein angiograms were taken using a 60 degree fundus camera and graded for the presence of leakage and capillary non-perfusion. There was a significant correlation between the severity of retinopathy and the amplitude and latency of the STR. There was a similar correlation with the amplitude and latency of the OPs, a weaker correlation with the amplitude of the PERG, but no significant correlation with the latency of the PERG. These results support an inner retinal origin for the STR and suggest a role for STR in the electroretinographic assessment of diabetic retinopathy.