Dyschromatopsia in Multiple Sclerosis Patients: A Marker of Subclinical Involvement?: Response.

Abstract

We thank Dr. Subramanian and colleagues for their critical appraisal and interest in our article (1). They suggested that Hardy–Rand–Rittler (HRR) pseudoisochromatic plates are not a sensitive indicator of acquired color vision deficits in patients with optic neuropathies. While we agree that a hue discrimination test such as the Farnsworth-Munsell (FM) 100 hue test is more sensitive than HRR plate testing, we chose the latter given the fact that it is widely available and easy to perform (2). Moreover, several studies have shown that HRR plates are an effective test of color vision as long as visual acuity is better than 20/50 (3). Use of HRR plates, when compared with the FM 100 hue test, is easier and quicker to perform, and almost all normal subjects would likely make no errors, while in the FM 100 hue test normal subjects would make a few mistakes (2). Zhao et al (4) also bring up an interesting hypothesis that HRR plate testing may be used to screen patients with multiple sclerosis for deficits in contrast sensitivity. One limitation of our study is that contrast sensitivity was not assessed. We look forward to future studies to further address this issue.