OBJECTIVE: To measure retinal vascular oximetry (oxygen saturation [SO2] and partial oxygen pressure [PO2]) and diameter in multiple sclerosis (MS) patients using a novel technology – the Oxymap® T1 Retinal Oximeter.
BACKGROUND: Optic neuritis (ON), a common manifestation of multiple sclerosis (MS), often results in optic atrophy, a clinical finding characterized by optic pallor and retinal vessel attenuation. To date, there is no objective in vivo method for measuring the magnitude of pallor or vascular attenuation.
DESIGN/METHODS: A cohort of healthy controls, and MS patients with prior unilateral ON underwent assessments with low-contrast letter acuity (LCLA) (2.5[percnt]), spectral-domain optical coherence tomography, and fundus photography. Further, using the Oxymap®, we measured the mean retinal vessel SO2, PO2, and diameter.
RESULTS: Compared to controls, we found that the mean retinal vascular SO2, and PO2, was higher in MS patients; particularly in eyes with prior ON. Alternately, the mean retinal vessel diameter was attenuated in MS eyes, when compared to those of controls. The higher SO2, PO2, and reduced retinal vessel diameter corresponded to decreased LCLA and retinal nerve fiber layer thickness (RNFLT).
CONCLUSIONS: To our knowledge, we report the first application of objective, in vivo, ascertainment of retinal oxygenation and vessel diameter in MS patients, and confirm differentiation (especially in ON-affected eyes) from measures derived from controls. Further, we demonstrate an inverse relationship between increased SO2 and PO2, and corresponding measures of LCLA and RNFLT. Alternately, a direct relationship was identified between retinal vessel diameter and LCLA and RNFLT. We hypothesize that the pathobiological mechanisms in MS, culminate in retrograde degeneration of retinal ganglion cells, thereby reducing metabolic demand, oxygen extraction, and retinal vessel caliber. The application of retinal oximetry in MS, may facilitate the development of visual system biomarkers, germane to the identification of novel neurotherapeutic strategies in MS treatment trials.