Progressive retinal neurodegeneration and microvascular change in diabetic retinopathy: longitudinal study using OCT angiography.

Aims: To investigate the association between progressive macular ganglion cell/inner plexiform layer (mGCIPL) thinning and change of optical coherence tomography angiography (OCTA)-derived microvascular parameters in early-stage diabetic retinopathy (DR).

Methods: A retrospective cohort study involved 40 eyes presenting with no DR or mild non-proliferative DR at baseline, and 30 healthy controls were included. All participants underwent spectral-domain OCT and OCTA at baseline and at 6, 12, 18, and 24 months. Change of mGCIPL thickness and OCTA metrics including foveal avascular zone (FAZ) area and FAZ circularity, vessel density (VD), and perfusion index (PI) was measured. Correlations between mGCIPL thickness and OCTA metrics were explored using regression models.

Results: Average progressive mGCIPL loss was 0.45 µm per year. Three microvascular parameters were significantly impaired at 24 months compared to baseline (FAZ area: 0.34-0.36 mm, VD: 18.9-18.5/mm, PI: 0.35-0.34). A strong positive correlation was found between loss of mGCIPL and VD from baseline to 24 months (r = 0.817, p < 0.001). Multivariable regression analysis showed that thinner baseline mGCIPL and greater loss of mGCIPL thickness (B = 0.658, p < 0.001) were significantly associated with change of VD.

Conclusions: In the early stage of DR, progressive structural retinal neurodegeneration and parafoveal microvascular change seem to be highly linked. Advanced mGCIPL thinning might precede microvascular impairment in early DR.