Longitudinal analysis of microvascular perfusion and neurodegenerative changes in early type 2 diabetic retinal disease

Aim To prospectively monitor subclinical changes in capillary perfusion and retinal layer thickness in patients with type 2 diabetes and early diabetic retinal disease over 2 years. Methods In this longitudinal study we performed biannual retinal vascular imaging using optical coherence tomography angiography (RTVue) to analyse the foveal avascular zone (FAZ) area, perimeter, acircularity index (AI) and parafoveal superficial/deep vessel density (VD). Spectral-domain optical coherence tomography (Spectralis) was used to measure the thickness of nine macular layers and the peripapillary nerve fibre layer. Results Among 117 eyes (58 left) of 59 patients (21 female), 105 had no diabetic retinopathy (DR), 6 mild and 6 moderate non-proliferative DR at baseline. We found DR progression in 13 eyes at year 2. The FAZ area (+0.008 +/- 0.002 mm(2)/year, p<0.0001), perimeter (+0.036 +/- 0.010 mm/year, p=0.006) and AI (+0.005 +/- 0.002/year, p=0.0280) increased significantly. A pronounced decrease was found in the superficial (-1.425 +/- 0.290%/year, p<0.0001) but not the deep VD. Inner neuroretinal loss was confined to the ganglion cell (-0.539 +/- 0.150 mu m/year, p=0.0004) and the inner plexiform layer (-0.361 +/- 0.127 mu m/year, p=0.0045). In the outer retina, we observed a statistically significant decrease in thickness in the outer plexiform, photoreceptor layer and pigment epithelium of -0.921 +/- 0.161 mu m/year, -0.325 +/- 0.139 mu m/year and -0.385 +/- 0.084 mu m/year, respectively. Conclusion Subclinical signs of microangiopathy and neurodegeneration appear in parallel and are highly progressive even in the earliest stages of diabetic retinal disease.