Inner retinal sensory neuropathy in persons with type 1 diabetes mellitus

Abstract

Purpose: To quantify differences in inner and outer retinal function between patients with type 1 diabetes mellitus (T1DM) with no to minimal diabetic retinopathy (DR) and healthy controls

Methods: In this cross-sectional pilot study, we examined 29 adults with T1DM and no to minimal DR and 25 age-matched healthy controls. Participants underwent a complete ocular examination, measurement of best-corrected visual acuity, and fundus photography for retinopathy grading. The right eye was arbitrarily chosen as the study eye. Contrast sensitivity testing, frequency doubling technology (FDT) perimetry, and the amplitude of the scotopic threshold response (STR) on electroretinography (ERG) were used to assess inner retinal function. Outer retinal function was assessed with dark adaptation testing. Parametric tests were used to analyze normally distributed variables, and non-parametric tests were used to evaluate non-normally distributed variables. Subgroup analyses were performed for T1DM participants with > and ≤ 15 years duration of diabetes.

Results: 15 T1DM participants (52%) had no retinopathy, 11 (38%) had mild retinopathy, and 3 (10%) had moderate retinopathy. FDT mean deviation (MD) was significantly reduced in T1DM patients (MD ± SD = -1.49 ± 3.09 decibels (dB)) relative to controls (0.11 ± 3.44 dB) (p=0.026). Similarly, patients with T1DM exhibited a significant reduction in log contrast sensitivity (1.65 ± 0.08) compared to healthy controls (1.79 ± 0.13) (p<0.001). Individuals with T1DM for > 15 years (n=11) had significantly reduced STR amplitudes (3.8 ± 3.9 microvolts) vs. controls (9.2 ± 4.8 microvolts) (p=0.036), while STR amplitudes were similar between individuals with T1DM ≤ 15 and controls (p=0.37). There were no differences in dark adaptation between controls and any of the patients with T1DM (p=0.42).

Conclusions: These data suggest that patients with T1DM may exhibit an inner retinal sensory neuropathy as assessed by electrophysiologic and psychophysical tests in spite of having no to minimal DR. Further studies in a larger cohort are ongoing to understand how such retinal dysfunction might progress over time and to identify new means to prevent vision loss in patients with T1DM.

Keywords: 499 diabetic retinopathy • 461 clinical (human) or epidemiologic studies: natural history • 691 retina: proximal (bipolar, amacrine, and ganglion cells)