Abstract
Purpose: :
Focal cortical disturbances associated with multiple sclerosis, trauma or tumor can interfere with higher visual processing even in the presence of preserved visual acuity (VA). Diabetes affects both retinal vasculature and neurons, but its effects on the CNS are less well described. We hypothesized that DM patients exhibit central visual processing deficits compared with non-DM controls.
Methods: :
Subjects aged 20-69 with >0.5 logMAR ETDRS VA and varying stages of diabetic retinopathy (non-proliferative, severe untreated proliferative (PDR), severe PDR + pan-retinal photocoagulation, PRP), and non-DM controls underwent standard and psychophysical testing: monocular color vision (FM100Hue), binocular illusory contours (IC), motion-defined letter recognition (MDR), Titmus fly stereoacuity and Pelli-Robson contrast sensitivity. After ensuring shape recognition, 5 IC and 1 control shape were presented at 2 support ratios (0.2 and 0.4, luminance-defined versus total contour length) at varying contrast levels. Thereafter, increasing support ratios (0.1-0.6) were presented at maximal contrast. MDR thresholds were scored at 55% correct recognition.1
Results: :
Eight DM and 7 non-DM subjects were enrolled (mean age 48, 7 males, 8 females). Mean logMAR VA was 0.09 (+/-0.07 SEM; -0.26 to 0.48 range) and 0.03 (+/-0.02 SEM; -0.02 to 0.1 range) for DM and non-DM subjects, respectively. There were significant differences in colour vision total error scores across all axes, contrast sensitivity and IC detection between DM and non-DM subjects (one-way ANOVA, p<0.05). Increasing contrast and support ratios improved IC identification across all groups; despite this, patients treated with PRP displayed severe deficits. At high support ratio (0.5), all groups achieved >80% correct IC identification. No significant difference (ANOVA, p>0.05) was detected in MDR or stereoacuity between groups.
Conclusions: :
Our data to date suggest that DM may affect perception of illusory contours but does not influence motion detection. It confirms previous knowledge that DM impairs colour vision and contrast sensitivity. This ongoing study will be expanded to include additional patients per study arm and visual electrophysiology.1. Regan et al. Visual Processing of Motion-defined Form. The Journal of Neuroscience 1992: 12, 2198-2210.
Keywords: diabetic retinopathy • visual cortex • shape, form, contour, object perception