Abstract
Relapsing remitting multiple sclerosis (RRMS) may cause primary retinopathy, which reflects central nervous system atrophy. This study aimed to assess the outer retinal layers in RRMS patients with and without optic neuritis (ON) functionally by multifocal electroretinography (mf-ERG) and structurally by spectral-domain optical coherence tomography (OCT). This case-control study evaluated the eyes of 30 RRMS patients and 30 age - and sex-matched healthy subjects using mf-ERG and OCT. There was a significantly lower amplitude and delayed peak time of all five retinal rings in MS-ON and MS-non-ON eyes than in controls (p-values ≤ 0.05). However, most mf-ERG parameters showed no statistically significant difference between ON and non-ON eyes, except for a delayed peak time in R2 (p-value = 0.004) and a lower amplitude in R3 (p-value = 0.012) in MS-ON eyes compared to MS-non-ON eyes. The thickness of the outer and inner retina was significantly decreased in MS-ON and MS-non-ON eyes compared to controls (p < 0.001), with no significant difference between MS-ON and MS-non-ON eyes. Functional and structural alterations of the bipolar and photoreceptor layers in the outer retina are present in RRMS with or without ON. Therefore, the outer retina could be a site for primary pathology in MS unrelated to the optic nerve affection.