Purpose: This purpose of this study was to find the association between severity of visual impairment and retinal nerve fiber layer (RNFL) thickness loss in different demyelinating diseases using optical coherence tomography (OCT) and, simultaneously, assess the fellow eye for subclinical RNFL thickness loss.
Methods: This cross-sectional, observational study included 60 eyes of 30 patients above the age of 20 years with diagnosed cases of multiple sclerosis (MS), neuromyelitis optica (NMO), and clinically isolated syndrome (CIS) who had history of (h/o) optic neuritis (ON) attack were included. Participants included in the study group underwent best-corrected visual acuity (BCVA) measurement, color perception, swinging flashlight test, slit-lamp examination, and dilated fundus examination (DFE). RNFL thickness was measured using spectral domain OCT (SD-OCT) (Optovue RTVue-V6.11 A Fourier). Intergroup analysis of RNFL thickness was done using a Chi-square test (P < 0.05 was considered significant). Spearman's rank correlation coefficient (Spearman'sρ) was used for association (ρ < 0.963 was considered significant).
Results: RNFL thickness was significantly reduced in patients with NMO than MS, while all patients of CIS had the highest RNFL thickening (P = 0.00048). Lower visual function scores correlated with reduced average overall RNFL thickness, and this association was statistically significant in affected (R = 0.942) and fellow eyes (R = 0.963).
Conclusion: The severity of visual impairment significantly correlated with the severity of axonal loss in affected as well as the fellow eye. NMO is associated with more widespread axonal injury in the affected optic nerve. Hence, RNFL thickness is an indicator of the progression of visual impairment in demyelinating diseases and OCT can help distinguish the etiology and, therefore, may be useful as a surrogate marker of axonal involvement in demyelinating diseases.
Keywords: Multiple sclerosis; neuromyelitis optica; optic neuritis; optical coherence tomography; retinal nerve fiber layer.