Association of Diabetic Neuropathy with Contrast Sensitivity Impairment and OCT Parameters in Type-2 Diabetic Patients without Retinopathy

PURPOSE: To demonstrate the retinal neurodegeneration findings caused by diabetes and diabetic neuropathy in patients without retinopathy, anatomically with spectral domain optic coherence tomography (SD-OCT) and functionally with contrast sensitivity.
METHODS: Presence of diabetic neuropathy was objectively revealed together with neurologists by electromyography (EMG). SD-OCT and contrast sensitivity were evaluated in patients with peripheral neuropathy (DPN+ group), without neuropathy (DPN- group) and healthy controls. Average and sectoral retinal nerve fiber layer (RNFL) thickness, average and 6 sectoral quadrants ganglion cell complex (GCC) were compared between groups. Also, contrast sensitivity (CS) measurement values were calculated between groups.
RESULTS: Although there were significant differences between three groups in the average RNFL, in pairwise comparisons there were no statistical difference in the average RNFL between the DPN (-) and healthy control groups (p=0,679). Average GCC thickness also showed significant differences between the three groups (p<0,001)]. The post hoc test performed to determine the group that made the difference, it was seen that the average ganglion cell values of the DPN+ group were lower than the other groups. Also noteworthy, when the diabetic group with "no neuropathy" compared to the healthy control group, GCC values were significantly lower in the diabetic group. When the DPN- group compared with healthy group, contrast sensitivity values were significantly lower in the diabetic group (p<0,001). Analysis of mesopic contrast sensitivity values and each of the average RNFL and GCC thickness indicated significant positive correlations (r=0.238, 0.326 respectively).
CONCLUSION: Our results suggest that there is evidence of early retinal neuronal damage, particularly on SD -OCT, before DPN occurs in patients with type 2 DM. Though visual acuity is unaffected in diabetic patients, decreased CS and GCC may be an early warning for DPN.