Abstract
Abstract: :
Purpose: Previous studies have investigated the multifocal ERG (mfERG) in diabetic patients with and without diabetic retinopathy. The effect of changes in blood glucose itself on the mfERG have never been investigated. With glucose clamp technique, any given blood glucose concentration can be achieved and maintained in a test subject by infusion of glucose at a continuously adjusted rate and infusion of insulin at a fixed rate. The purpose of this study was to investigate the effect of both long and short-term changes in blood glucose on implicit time (IT) and amplitude of the mfERG in diabetic patients without retinopathy. Methods: We investigated the effect of hyperglycemia on the mfERGs of 15 type 1 diabetic patients without diabetic retinopathy. Mean age was 37 years (27-50), range of duration was 7-19. MfERGs (Veris 4.3) were recorded for each subject twice on the same day, one recording was performed during euglycemia (5 mmol/l) and one recording during hyperglycemia (15 mmol/l). Prior to each recording, blood glucose was maintained at a steady level, i.e. 5 or 15 mmol/l, for 75 min. Patients were randomized to start on either 5 or 15 mmol/l. The implicit times and amplitudes of the three major components (N1, P1, and N2) of the mfERG recorded during euglycemia were compared to the implicit times and amplitudes recorded during hyperglycemia. Furthermore, the effect of high and low HbA1c on the mfERG were analyzed to evaluate the long-term effect of the blood glucose concentration on the amplitudes and implicit times of the mfERG. Results: When blood glucose was increased from 5 to15 mmol/l, the mean N2 IT decreased by 0.5 msec (p = 0.02), and the mean N2 amplitude increased by 1.01 nV (p = 0.03) when all 103 responses were analyzed collectively. For the regional analysis (6 concentric rings and quadrants), we found no significant regional difference in response to the change in blood glucose. We found no effect of the level of HbA1c on amplitude or implicit time of the mfERG. Conclusions: The short term effect of hyperglycemia on the mfERG is a small decrease in N2 IT and a small increase in N2 amplitude. The long-term blood glucose concentration did not effect the mfERG.
Keywords: electroretinography: clinical • metabolism • diabetic retinopathy