Visual accommodation and sustained visual resolution in multiple sclerosis

Many multiple sclerosis (MS) patients frequently experience transient blurring. We investigated the possibility that this symptom is due to the inability of patients to sustain an accommodative response to stimuli viewed at distances nearer than or farther from the individual tonus position of accommodation. In a group of MS patients and age-matched healthy control subjects, we measured (1) accommodative range and tonus position; (2) reaction time (RT) to detect a change in a small optotype (viewed in a Badal lens system) as a function of viewing distance; and (3) contrast sensitivity at a fixed viewing distance. MS patients did not differ significantly from healthy controls on near point, far point, pupil size, accommodative range, or tonus position measures. However, as a group, MS patients showed significantly slower RTs than controls to detect optotype changes for stimuli viewed at distances nearer to or farther from the individual tonus position of accommodation. All subjects showed significantly slower RTs to detect changes in optotypes viewed at extreme near and far optical distances compared to RTs to detect changes in stimuli viewed at the tonus position. This difference was significantly larger for MS patients than for controls. These data also suggest that dynamic dioptric factors contribute to the magnitude of contrast sensitivity deficits in this patient population and indicate that the relationship between the individual tonus accommodation position and viewing distance is an important variable in CS testing.