Optic neuritis (ON) is a frequent manifestation of demyelinating attack in multiple sclerosis (MS). Initial visual loss can vary from minimal to complete. Visual improvement occurs in about 95% of patients, some of them recovering to normal [visual acuity (VA), color vision, visual field (VF)]. We analyzed retinal ganglion cell layer (RGCL) thickness in MS patients who recovered their normal vision after ON to determine whether a relative preservation of RGCL existed in these patients.
We conducted a retrospective study of all patients with MS and ON examined by one of us (F. X. B.) between 2013 and 2018. Inclusion criteria were strictly unilateral ON, full recovery of vision, computerized visual field, and OCT examinations. Full recovery of vision was defined as VA ≥ 10/10, Ishihara ≥ 11/13, and VF mean defect (MD) ≤ 2.6 dB. Evaluation of RGCL was obtained with spectral domain optical coherence tomography (SD-OCT). The normal fellow eye of all patients served as the control group. Relative thinning of RGCL, expressed as percentage, was calculated by comparing results from the affected eye to the fellow eye of the same patient.
Twenty-one patients (21 affected eyes - Group 1, 21 normal fellow eyes - Group 2) satisfying the inclusion criteria were retrieved from our database. All patients exhibited the relapsing-remitting form of MS. There were 16 women and 5 men. Mean age was 39.3 years old. There were no statistically significant differences between Group 1 and Group 2 for either VA (p = 0.3934) or Ishihara (p = 0.140), but a significant difference was found for VF MD (p = 0.0405). A markedly significant difference for RGCL thickness (p = 0.0001) was found, without any correlation with the degree of visual recovery. A subgroup of patients (n = 14) was examined at the time of initial visual loss. We correlated their results of visual function to the final RGCL thickness, and a correlation was found between either the initial VA loss or the initial VF loss and the final loss of RGCL (R2 = 0.4075 and R2 = 0.00739, respectively).
In our study, all patients with ON lost a significant amount of RGCL despite a full recovery of vision, as defined by our criteria. The percentage of RGCL loss varied from 5 - 27% and could not be correlated with any final visual indices. However, a correlation was found with the degree of initial visual loss. Despite sometimes marked RGCL loss after ON, patients with MS can recover normal visual function, according to standard clinical tests.