Reduced metabolic function and structural alterations in inherited retinal dystrophies: investigating the effect of peripapillary vessel oxygen saturation and vascular diameter on the retinal nerve fibre layer thickness

Purpose To evaluate the relationship between the peripapillary metabolic alterations [retinal vessel Oximetry (RO)] and the structural findings [retinal vessel diameter and retinal nerve fibre layer thickness (RNFL)] in patients with inherited retinal dystrophies (IRD). Methods Patients with IRD [24 patients with rod-cone dystrophy (RCD), 15 patients with cone-rod dystrophy, 13 patients with inherited maculopathy] and 18 age-matched controls, who underwent RO imaging and spectral domain optical coherence tomography, were included. The average and quadrant oxygen saturation in all four major peripapillary retinal arterioles (A-SO2) and venules (V-SO2) were measured, and their difference (A-V SO2) was calculated. The corresponding retinal vessel diameter of these arterioles (D-A) and venules (D-V) was measured. The data were compared to the peripapillary RNFL thickness within the IRD subgroups and to the data obtained in the controls. Results In general, patients with IRD had higher average V-SO2 values when compared to controls (p ≤ 0.029). Rod-cone dystrophy (RCD) patients differed from controls, but also from patients with other IRDs, when the average and quadrant oxygen saturation values (A-SO2 and V-SO2) were evaluated (p ≤ 0.026). Within the RCD group, the correlations of RNFL thickness to V-SO2, A-V SO2, D-A and D-V were significant (p ≤ 0.030), thus indicating a different relationship between the RNFL thickness and the examined parameters, when compared to the other groups. Conclusion It becomes evident from our combined metabolic–structural approach that a prediction model, to identify which individual is at risk of developing a photoreceptor degeneration of RCD type, can be proposed. It will take into account the peripapillary retinal oxygen saturation, the retinal vessel diameter and the RNFL thickness values.