Retinal vessel oxygen metabolism correlates with photoreceptor degeneration in retinitis pigmentosa

To measure the retinal vessel oxygen saturation function with retinal oximetry (RO) and correlate these findings with structural retinal photoreceptor adaptive optics (AO) imaging in patients with retinitis pigmentosa (RP) and controls.

Prospective observational study examining 43 eyes of 23 subjects: 22 eyes from 12 patients with RP (4♀ 8♂; 46.4 ± 15.0 years) and 21 eyes from 11 controls (5♀ 6♂; 38.1 ± 12.7 years). Main outcome measures were the mean arterial (A-SO₂; %), venular (V-SO₂; %) oxygen saturation, as well as their difference (A-V SO₂; %) measured with the oxygen saturation tool of the Retinal Vessel Analyzer (IMEDOS Systems UG, Germany) and the mean cone density (AO-D; cells/mm²) in 12 predefined regions of interest (ROI) arranged at 1.5°, 3°, and 4.5° eccentricity from the foveal center.

RP eyes demonstrated significantly increased A-SO₂ and V-SO₂ and a reduced A-V SO₂ compared to controls (all p < 0.001), indicating impaired retinal oxygen extraction. In addition, both arterial and venular vessel diameters were significantly reduced in RP (p < 0.001). Adaptive optics imaging revealed a significant reduction in cone density across all eccentricities in RP compared to controls (p < 0.01). Linear regression analysis showed a negative correlation between A-SO₂ and AO-D (r = - 0.169, p < 0.001) and a negative correlation between V-SO₂ and AO-D (r = - 0.316, p < 0.001). In contrast, A-V SO₂ correlated positively with AO-D (r = 0.27, p < 0.001). Cone density also correlated positively with both arterial (r = 0.406, p < 0.001) and venular (r = 0.346, p < 0.001) vessel diameters.

RP is associated with increased retinal oxygen saturation, reduced oxygen extraction, vascular narrowing, and decreased photoreceptor density. The observed correlations between retinal oxygen metabolism, vascular structure, and photoreceptor integrity suggest a close coupling between metabolic and structural alterations in RP. Evaluating retinal oxygen metabolism in conjunction with high-resolution structural imaging may provide deeper insight into disease mechanisms and progression in inherited retinal degeneration.