Abstract
Purpose: :
The purpose of this study was to determine the degree of retinal nerve fiber layer (RNFL) thinning by optical coherence tomography (OCT) that is associated with losses of low- and high-contrast acuity over time in a multiple sclerosis (MS) cohort. Visual dysfunction and axonal loss are common in MS. The emergence of OCT has allowed us to capture the unique structure-function correlations provided by the anterior visual pathway in MS.
Methods: :
Patients with MS underwent OCT-3 imaging at baseline and at 6-month intervals during a mean follow-up period of 1.5 years (range 0.5-3.7) at three academic centers. RNFL thickness was measured for 360º around the optic disc. Visual function testing was performed using low-contrast (2.5 and 1.25% levels) and ETDRS acuity charts. Eyes with comorbid ocular conditions or acute ON within 3 months prior to testing were excluded.
Results: :
Among 1,148 patients (2,296 eyes, age 44±11 years) who underwent baseline assessments, 365 (725 eyes) have participated in longitudinal follow-up. Worsening of low-contrast acuity was noted in 237 eyes of 123 patients (33% of MS eyes). Approximately 1/3 of eyes with visual loss had a past history of ON. Two-line (10-letter) losses of low-contrast acuity were associated, on average, with 1.6 µm decrements in RNFL thickness over time at 2.5% contrast (p=0.009, GEE models, accounting for age and within-patient, inter-eye correlations), and 3.7 µm reductions at 1.25% contrast (p=0.02). Patients with worsening vision were only slightly older (age 45 vs. 43 years), and had slightly greater disease duration (12 vs. 11 years).
Conclusions: :
Visual loss occurs in a substantial proportion of MS eyes, and may be present even in the absence of a history of ON. Reductions in low-contrast acuity are associated with RNFL thinning over time, suggesting that axonal loss may be a significant contributor to visual dysfunction in MS.
Keywords: nerve fiber layer • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • visual impairment: neuro-ophthalmological disease