Spatio-temporal contrast sensitivity in Parkinson's patients and age-equivalent controls

The elderly suffer from a higher incidence of visual problems than does the rest of the population. Older individuals often report recurrent visual problems which may persist in individuals with no apparent occular pathology and with normal or near-normal acuity. However, elderly individuals are not the only populations that report ill-defined visual difficulties. Many patients with various neurologic conditions also report vague visual problems which persist in spite of normal or near-normal acuity.

Research is now indicating that traditional tests of visual acuity do not adequately assess how well a person sees. An alternative to traditional vision tests is Contrast Sensitivity (CS) testing. CS is a vision test that systematically varies contrast and frequency, thus measuring the ability to see targets covering the full range of object sizes encountered in daily activities. By detecting visual deficiencies at a wide variety of spatial frequencies, CS allows a more detailed assessment of visual capacity.

The present study investigated the relationship between spatial frequency and temporal modulation with respect to their impact on the contrast sensitivity of Parkinson's patients and age-equivalent controls. Individuals in various stages of the disease were assessed to evaluate how CS is affected by the progression of Parkinson's disease. Results from the study revealed distinct differences between Parkinson's patients and controls with respect to CS, as well as significant differences between the four stages of Parkinson's disease evaluated in this study. Temporal modulation and spatial frequency were found to have a significant impact on contrast sensitivity, both independently and in an interactive fashion. Specifically, these results indicated that in order to maximize CS for Parkinsonians and controls in the widest possible range of circumstances, a slow pulsing modulation is optimal. Lack of modulation was found to be extremely detrimental at very low spatial frequencies, but did not have as negative an impact at mid- and high-range spatial frequencies. These findings indicate that, whenever possible, it is important to take into consideration the range of spatial frequencies involved in a task and choose the temporal modulations that are most advantageous for the circumstances.