Background: Neuromyelitis optica (NMO) is a recurring inflammatory neurological disease characterized by severe optic neuritis and myelitis. The purpose of this study was to determine whether the retinal nerve fiber layer thickness (RNFLT) is correlated with the clinical presentations in patients with NMO and to determine the clinical factors that lead to poor visual outcomes.
Methods: Thirty-five eyes of 18 patients with the NMO spectrum and 28 eyes of 14 patients with multiple sclerosis (MS) were studied. All of the patients had at least one episode of optic neuritis (ON) >6 months before being studied. The eyes were classified into four groups based on an episode of ON: NMO-ON, NMO eyes with at least one episode of ON; NMO-nonON, NMO eyes without an episode of ON; MS-ON, MS eyes with at least one episode of ON; and MS-nonON, MS eyes without an episode of ON. The RNFLT was measured by optical coherence tomography (OCT). The correlations between the RNFLT and the clinical data were determined.
Results: The overall RNFL was thinner in patients in the NMO-ON group than in the MS-ON group (63.84 µm vs. 84.28 µm; p = 0.0006) especially in the superior and inferior quadrants. The overall RNFLT was significantly correlated with the best-corrected visual acuity (BCVA) in both the NMO groups (r = 0.67; p < 0.0001) and the MS groups (r = 0.62; p = 0.0097). The overall RNFLT was negatively correlated with the number of relapses in the NMO group. A receiver operating characteristic (ROC) analysis showed that the cut-off value for a decrease in visual acuity to <20/20 was 71.41 µm of the overall RNFLT in the NMO group. The frequency of the ON relapses and the time for beginning the treatment with high-dose intravenous methylprednisolone (HIMP) significantly affected the preservation of the RNFLT.
Conclusions: The overall thinner RNFL in eyes with NMO than in eyes with MS indicates a greater loss of optic nerve axons in eyes with NMO. An early intervention with HIMP and preventing recurrences in NMO are critical for minimizing the axonal loss. Our findings indicate that OCT is an important method of evaluating loss of optic nerve axons in eyes with NMO and MS.