Higher retinal vessel oxygen saturation: investigating its relationship with macular oedema in retinitis pigmentosa patients

Purpose Primary objective-to investigate the effect of retinal vessel oxygen saturation (SO2) on macular oedema (ME) in retinitis pigmentosa (RP) patients. Secondary objective-to link the presence of ME to metabolic (oxygen saturation of retinal vessels, SO2), functional (multifocal electroretinography, mfERG) and structural (Spectral Domain Optical Coherent Tomography, SD-OCT) alterations in RP. Design Prospective, cross-sectional, non-interventional study. Subjects Patients with typical RP (N= 37) and controls (N = 19), who underwent retinal vessel Oximetry (RO), SD-OCT and mfERG, were included. Methods A computer-based program of the retinal vessel analyser unit (IMEDOS Systems UG, Jena, Germany) was used to measure SO2. We evaluated the mean SO2, in all major retinal arterioles (oxygen saturation in retinal arterioles, A-SO2, %) and venules (oxygen saturation in retinal venules, V-SO2, %). MfERG responses were averaged in zones (zone 1 (0-3 degrees), zone 2 (3-8 degrees) and zone 3 (8-15 degrees)) and compared to corresponding areas of the OCT. The effect of ME on SO2 was evaluated dividing the RP in two subgroups: with clinical appearance of ME (ME-RP) and without it (no-ME-RP). Main outcome measures Parallel recording and juxtaposition of metabolic (SO2) to structural (OCT) and functional(mfERG) measures. Mean (+/- SD) A-SO2 and V-SO2 were higher in no-ME-RP (96.77% (+/- 6.31) and 59.93% (+/- 7.76)) and even higher in the ME-RP (99.82% (+/- 6.21) and 65.63% (+/- 7.63)), compared to controls (93.15% (+/- 3.76) and 53.77% (+/- 3.70), p <= 0.006). Results The subgroup ME-RP differed significantly from the subgroup no-ME-RP by increased A-SO2 and V-SO2, p <= 0.026. The presence of ME confirmed a different relationship between the altered SO 2 and the vessel diameters, against the functional and structural parameters. Conclusion Based on our results, the presence of macular oedema indicates a tendency toward greater alteration of the metabolic function in RP patients.