Retinal neurovascular changes appear earlier in type 2 diabetic patients

Purpose: To investigate the early neurodegenerative changes of inner retina and choroid in type 1 and type 2 diabetic patients without retinopathy and with early-stage retinopathy. Methods: In this observational cross-sectional study, 90 right eyes of 90 naive type 1 and 2 diabetic patients without diabetic retinopathy (DR) and with mild to moderate nonproliferative DR (NPDR) were analyzed. Forty healthy eyes were included as controls. We used spectral-domain optical coherence tomography to evaluate the ganglion cell complex (GCC) thickness, the retinal nerve fiber layer (RNFL) thickness, the choroid thickness, and the central foveal thickness (CFT) of patients and controls. Results: Average GCC thickness turned out to be thinner in type 2 diabetic patients with no DR and with NPDR compared to controls (p = 0.046 and p = 0.041, respectively). The RNFL thickness and CFT were similar among the studied groups and compared to controls (p = 0.78 and p = 0.104, respectively). Average choroid thicknesses (both in the subfoveal area and in a 1-mm radius circular area) were significantly thinner in type 2 diabetic patients with no DR and NPDR, compared to DMT1 groups and controls (both p<0.0001). The GCC and choroid thickness changes were not correlated in any of the investigational groups. Conclusions: Type 2 diabetic patients without retinopathy and with early-stage retinopathy have inferior thickness values of GCC and choroid compared to controls. Insulin resistance might be a possible adjunctive pathogenetic aspect of neurodegeneration.