The aim of the study was to assess changes in the retinal nerve fibre layer (RNFL) and in retinal oxygen saturation [arterial (AS), venous (VS) and arterio-venous (A-V) difference] in the affected and unaffected eye during a six-month follow-up in patients with history of recent optic neuritis (ON).

Previous cross-sectional studies reported alterations of retinal oxygen saturation in ON, but there has been no longitudinal evaluation of the retinal saturation changes in ON.

Fifty patients with ON due to multiple sclerosis (MS) within 3 months of onset of symptoms were enrolled (17 males, mean age 35.3). All patients were examined at baseline (V1) and after 6 months (V2) using optical coherence tomography (OCT) to get retinal nerve fibre layer (RNFL) values, and automatic retinal oximetry to obtain saturation values.

At V1, AS was significantly increased in affected eye compared to unaffected eye (99.5% vs. 98%, p = 0.03). Significant decrease in A-V difference from baseline was detected in both eyes (for ON eye: 32% vs. 29%, p = 0.004; for fellow eye: 31.4% vs. 30%, p = 0.04). At V1, there were no significant differences in RNFL, significant loss of RNFL was confirmed in the affected eye at V2 (95 μm vs. 86 μm, p = 0.0002) and in comparison to the fellow eye (86 μm vs. 94 μm, p = 0.0002).

Retinal oximetry is altered in both eyes in MS patients with unilateral ON. During the course of the disease, the retinal oxygen consumption decreases to a different degree in each eye and this change is not completely followed by changes in the RNFL thickness, suggesting either sub-clinical ON or systemic effects in the clinically unaffected eye.