New low-contrast vision charts: reliability and test characteristics in patients with multiple sclerosis

The quantitative assessment of visual function in multiple sclerosis (MS) c linical trials has been limited to Snellen visual acuity. The purpose of th is study was to examine the inter-rater reliability and test characteristic s of a new visual outcome measure, the Low-Contrast Sloan Letter Charts, in Patients with MS and visually-asymptomatic volunteers. Contrast letter acu ity scores (letter scores) were measured or each of four contrast levels (1 00, 5, 1.25 and 0.6%) by two independent raters. Inter-rater agreement was described with the intraclass correlation coefficient (ICC) and comparison of mean scores. Excellent inter-rater agreement (ICC=0.86-0.95) was demonst rated at each contrast level among MS Patients (n=100) and visually-asympto motic volunteers (n=33). Average letter scores at the lowest contrast level (0.6%) were highly variable in the MS group, even among patients with visu al acuities of 20/20 or better, and among those who required no assistance for ambulation. Low-Contrast Sloan Letter Chart testing is a highly reliabl e method of visual assessment, and Provides information on on aspect of neu rologic impairment in MS which is not captured by Snellen visual acuity or ambulation status. This new method demonstrates excellent Potential as a vi sual function outcome measure for future MS clinical trials.