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A.J. Adams, J.S. Ng, M.A. Bearse, Y. Han; Differences Between Type 1 and Type 2 Diabetics in the Multifocal Electroretinogram (mfERG) . Invest. Ophthalmol. Vis. Sci. 2005;46(13):344.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine whether differences in mfERG measures exist between type 1 and type 2 diabetic patients of similar diabetes duration. Methods: We conducted a retrospective analysis of one eye of each of 8 type 1 and 8 type 2 diabetic subjects. The groups were matched in duration of diabetes (mean type 1: 13.1 ± 10.5 yrs; type 2: 10.6 ± 6.4 yrs) and retinopathy level, but differed in age (type 1: 37.2 ± 11.3 yrs; type 2: 55.2 ± 7.8 yrs). Three subjects in each group had mild to moderate non–proliferative diabetic retinopathy, mostly microaneurysms outside of the central 7 deg, and 5 subjects in each group had no signs of retinopathy. 30 age–similar controls (44.5 ± 11.5 yrs) were also examined. MfERGs were recorded using VERIS 4 (103 elements covering the central 45 deg, dilated pupils, and 10–100 Hz filtering). First–order mfERG implicit time (IT) and amplitude (AMP) were derived using a template stretching method (Hood & Li, 1997). For each subject, IT and AMP measures were averaged across the 103 retinal locations. Analysis using 5 concentric rings was also performed. The groups were compared using two–tailed t–tests. Blood glucose level at the time of mfERG testing and HbA1c level were also examined. Results: Mean ITs (type 1: 28.9 ± 0.78 ms; type 2: 30.7 ± 0.88 ms; controls: 28.7 ± 0.72 ms) differed between the diabetic groups (p<0.01), as well as between type 2 diabetics and controls (p<0.01). The ring analysis showed that the ITs of the diabetic groups differed in all rings outside of the central 7 deg (p<0.001). The ITs of type 2 subjects also differed from the control group outside of the central 7 deg (p<0.001). A small, statistically significant difference was seen for mean ITs as a function of age within the control group (R2=0.27, p<0.01). The mean ITs of the diabetic groups remained significantly different after adjusting for the effect of age (p<0.001). No significant differences in AMP were found among the type 1, type 2, and control groups. Blood glucose (p=0.51) and HbA1c (p=0.80) levels did not differ between the diabetic groups. Conclusions: Implicit times of type 2 diabetics are abnormally delayed compared to type 1 diabetics and controls even after attempting to match diabetic duration and retinopathy level, and adjusting for age. Delays in diagnosis of type 2 diabetes may have contributed to their increased implicit times, as both the total duration and the duration of uncontrolled/untreated diabetes may have been underestimated.
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