Retinal Oxygenation in Inherited Diseases of the Retina

Abstract

(1) Background: The aim of our study was to investigate the relationship between retinal metabolic alterations (retinal vessel oximetry, RO) and structural findings (retinal vessel diameter, central retinal thickness and retinal nerve fiber layer thickness, RNFL) in patients with inherited retinal diseases (IRDs). (2) Methods: A total of 181 eyes of 92 subjects were examined: 121 eyes of 62 patients with IRDs were compared to 60 eyes of 30 healthy age-matched controls. The retinal vessel oximetry was performed with the oxygen saturation measurement tool of the Retinal Vessel Analyser (RVA; IMEDOS Systems UG, Jena, Germany). The 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. Additionally, retinal vessel diameters of the corresponding arterioles (D-A; µm) and venules (D-V; µm) were determined. The peripapillary central retinal thickness and the RNFL thickness were measured using spectral domain optical coherence tomography (SD-OCT) (Carl Zeiss Meditec, Dublin, CA, USA). Moreover, we calculated the mean central retinal oxygen exposure (cO2-E; %/µm) and the mean peripapillary oxygen exposure (pO2-E; %/µm) per micron of central retinal thickness and nerve fiber layer thickness by dividing the mean central retinal thickness (CRT) and the RNFL thickness with the mean A-V SO2. (3) Results: Rod-cone dystrophy patients had the highest V-SO2 and A-SO2, the lowest A-V SO2, the narrowest D-A and D-V and the thickest RNFL, when compared not only to controls (p ≤ 0.040), but also to patients with other IRDs. Furthermore, in rod-cone dystrophies the cO2-E and the pO2-E were higher in comparison to controls and to patients with other IRDs (p ≤ 0.005). Cone-rod dystrophy patients had the lowest cO2-E compared to controls and patients with other IRDs (p ≤ 0.035). Evaluated in central zones, the cO2-E was significantly different when comparing cone-rod dystrophy (CRD) against rod-cone dystrophy (RCD) patients in all zones (p < 0.001), whereas compared with controls and patients with inherited macular dystrophy this was observed only in zones 1 and 2 (p ≤ 0.018). The oxygen exposure was also the highest in the RCD group for both the nasal and the temporal peripapillary area, among all the evaluated groups (p ≤ 0.025). (4) Conclusions: The presented metabolic-structural approach enhances our understanding of inherited photoreceptor degenerations. Clearly demonstrated through the O2-E comparisons, the central and the peripapillary retina in rod-cone dystrophy eyes consume less oxygen than the control-eyes and eyes with other IRDs. Rod-cone dystrophy eyes seem to be proportionally more exposed to oxygen, the later presumably leading to more pronounced oxidative damage-related remodeling.

The Presence of Hyperreflective Foci Reflects Vascular, Morphologic and Metabolic Alterations in Retinitis Pigmentosa

“…Furthermore, the present study shows that the retinal vessel diameters are affected in RP [ 22 , 23 , 24 ]. Consistent with the results of published studies [ 22 , 23 , 33 , 34 , 36 , 37 ], we found once again an increased A-SO 2 and even more, an increased V-SO 2 in in RP group.…”

“…Consistent with the results of previous studies [ 22 , 23 , 33 , 34 , 36 , 37 ] our RP patients showed again altered metabolic function by means of increased oxygen saturation of retinal arterioles and venules. Oxygenation of the human retina is a dynamic process, and regulation is necessary to provide a healthy metabolic environment [ 63 ].…”

“…Recent RO studies on adults and children affected by RP showed an altered oxygen metabolism, by means of increased retinal vessel oxygen saturation and reduced oxygen consumption [ 31 , 32 , 33 , 34 , 35 ]. As the highest amount of oxygen is used by retinal photoreceptors, a reduction in retinal oxygen demand with a secondary increase in the retinal vessel saturation values following cellular apoptosis has been hypothesized [ 22 , 23 , 33 , 34 , 36 , 37 ].…”

Macular Imaging

“…Human retina metabolism is supported by oxygen supply, and abnormality in oxygen perfusion is linked to various ischemic and degenerative retinopathies, leading to visual impairment and blindness [99,100]. Oxygenation of the human retina is an energy-dependent process in which different mechanisms maintain the regulation [100].…”

Variability of Retinal Oxygen Metrics in Healthy and Diabetic Subjects

“… 6 – 10 Furthermore, there are reports of retinal oxygenation changes due to retinal vascular occlusions, 11 – 13 retinopathy of prematurity, 14 and inherited retinal degenerations. 15 , 16 Moreover, measurements of retinal oxygen saturation and metabolism have been reported in exudative age-related macular degeneration, 17 glaucoma, 12 , 18 – 20 and sickle cell retinopathy. 1 …”