Primary visual cortex impairment due to trans-synaptic degeneration after optic neuritis: A systematic review of neuroimaging studies.

Trans-synaptic degeneration (TSD) has been considered as a plausible mechanism in the visual pathway. However, the consequences of optic neuritis in the optic pathways and primary visual cortex (V1) are not well established. To address this gap, we conducted a systematic review of the literature, registered in PROSPERO (no. 42023479709), aiming to evaluate primary visual cortex impairment due to TSD following optic neuritis. On July 25th, 2023, the electronic databases EMBASE, PubMed, and Scopus were searched to identify eligible publications. Quality assessment was performed using the ROBINS-I tool. Out of 130 studies identified, 10 met the inclusion criteria. Using neuroimaging techniques such as diffusion tensor imaging (DTI) and structural magnetic resonance imaging (MRI), nine observational studies in multiple sclerosis (MS) (n = 863 participants) and one observational study on neuromyelitis optica spectrum disorder (NMOSD) (n = 60 participants) showed a significant reduction of the primary visual cortex volume and thickness and an important damage to the integrity of optic radiation, with decreased fractional anisotropy (FA) {Cohen's d (95 % CI): -1.17 [-1.48, -0.86]} and increased mean diffusivity (MD) {Cohens'd (95 % CI): 1.147 [0.807, 1.488]} in patients with optic neuritis, compared to healthy controls. The findings suggest that TSD affects the optic pathways after optic neuritis in these demyelinating diseases, in which damage to the optic nerve led to degeneration in the primary visual cortex, with consistent neuroimaging evidence of white matter integrity loss and cortical atrophy. No analyses of other optic neuropathies were found in the reviewed studies. We encourage future research to standardize imaging protocols and explore various etiologies of optic neuritis.