Abstract
Purpose:
Recently, we introduced and showed the effectiveness of an index of non-uniformity (ION) for neuroretinal function based on multifocal electroretinogram (mfERG) parameters (Bearse et al. 2014, ARVO E-abstract 4421). This index quantifies the non-uniformity of dysfunction across the central retina produced by diabetes. In a pilot study, we now examine longitudinal changes of the ION in adult type 2 diabetes (T2DM), which could contribute to predictive models of retinopathy in the future.
Methods:
One eye of 17 T2DM patients without retinopathy had 103 photopic mfERGs recorded from the central 45 deg. Patients were retested 10-14 months later (mean = 12.3±1.0 months). Local mfERG implicit times (IT) and N1-P1 amplitudes (AMP) were measured using template-scaling (Hood & Li, 1997). A control group’s (n=47) 103 local IT and AMP averages were calculated. Each subject’s local IT and AMP values were divided by the appropriate local control average and converted to dB. Then, the standard deviations of these values were computed within each eye to generate an IT ION and an AMP ION. We also measured systolic (SBP) and diastolic blood pressures (DBP), body mass index (BMI), random blood glucose (RBG) and HbA1c at each exam. At exam 1, the patients were 55.3±9.0 yrs old, with 11.3±6.0 yrs T2DM duration. Longitudinal changes of measurements were calculated and converted to percentages. Associations between the IONs and the other measures were examined using linear regression and P-values < 0.05 were considered to be significant.
Results:
At exam 1, IT ION and mean IT were correlated, as were AMP ION and mean AMP. However, no correlations were observed between either IT ION change and mean IT change, or between AMP ION change and mean AMP change. IT ION and AMP ION changes were, themselves, correlated. IT and AMP ION changes were not correlated with changes in RBG or HbA1c. However, IT ION change was correlated with SBP and DBP changes, and AMP ION change was correlated with BMI change and marginally correlated (P=0.05) with DBP change.
Conclusions:
Change in the non-uniformity of retinal dysfunction provides different information than average retinal function change in adult T2DM. Because IT and AMP ION changes in T2DM are correlated with blood pressure and/or BMI changes, it is possible that they are affected primarily by changes in vascular health.