Optic Neuritis and Multiple Sclerosis: Delay of Retinal Nerve Fiber Layer Thinning Measured by Optical Coherence Tomography

Abstract

Purpose: : To evaluate the delay of retinal nerve fiber layer (RNFL) thinning measured by optical coherence tomography (OCT) after optic neuritis (ON).

Methods: : A retrospective study of patients who had a single ON episode in one or both eyes. We divided patient OCTs into 5 groups, according to the intervals between ON onset and OCT: less than 1 month, 1 to 3 months, 3 to 6 months, 6 months to 1 year, and more than 1 year. The results were analysed by separate analyses of RNFL thickness in non-affected and affected eyes respectively, using an ANOVA with one factor, which was the interval between RBON onset and OCT. We then studied the OCTs performed more than a month after the onset of ON in the affected eyes. They were divided into 3 groups, according to patients’ neurological status: normal Magnetic Resonance Imaging (MRI), abnormal MRI, and clinically defined multiple sclerosis (MS). For this analysis, we used a separate-slopes model with the RNFL thickness as the dependent variable, the delay as a covariate and the neurological status as the categorical variable.

Results: : We included 52 OCTs of eyes with ON and 42 of non-affected eyes from 28 patients (24 women and 4 men). Their ages ranged from 22 to 57 years (mean: 35). In all, 30 eyes were affected, and 26 were non-affected. The interval factor had a significant effect on mean RNFL thickness in affected eyes (F (4, 45) = 12.1, p < 0.001) and in non-affected eyes (F (4, 37) = 3.03, p < 0.05). Post-hoc tests showed significant RNFL thinning for eyes with ON as from the 6^th month. For non-affected eyes, thinning was only observed 1 year after ON. For eyes with ON, the separate-slopes model showed a significant interaction between the delay and the neurological status (F (3, 28) = 7.21, p=0.0010).

Conclusions: : OCT measures RNFL atrophy after a single acute ON episode or in MS independently of any such episode.Thinning differs according to patients’ neurologic status. The thinning of the RNFL thickness can be measured as from the 6^th month after ON. Our results suggest that the thinning was faster in the group with an abnormal MRI and in the group with confirmed MS, than in the isolated ON group, and that MS patients already had thinner RNFLs at the start of their acute ON episode. This is consistent with the RNFL atrophy found in non-affected eye without any acute episode. This thinning can be the correlate of the cerebral atrophy found in MS patient with magnetic resonance imaging.

Keywords: neuro-ophthalmology: optic nerve • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • nerve fiber layer