Visual contrast sensitivity in patients with impairment of functional independence after stroke

Abstract

Background: Stroke has been considered a serious public health problem in many countries, accounting for complex disorders involving perception, such as visual, cognitive and functional deficits. The impact of stroke on the visual perception of individuals with impairments in functional independence was investigated.

Methods: We measured changes in functional independence and visual function in 40 patients with stroke (M = 52.3, SD = 0.65) and 10 controls (M = 52.5, SD = 0.66). The patients were divided into four subgroups following the Barthel Index (Group A: 20-35, serious dependence; Group B: 40-55, moderate dependence; Group C: 60-95, mild dependence; and Group D: 100 points, independence). Visual function was evaluated using the Contrast Sensitivity Function (CSF). The contrast threshold was measured using a temporal, two-alternative, forced-choice psychophysical method.

Results: The results show significant differences in CSF between healthy volunteers and patients with stroke (F (1.56) = 151.2, p < 0.001) for all frequencies (F (2.56) = 125.96, p < 0.001). The results also show that patients with low functional independence had lower contrast sensitivity than those with greater functional independence (F (3.56) = 344.82, p < 0.001).

Conclusions: An association exists between CSF and a worsening in the functional potential for performing daily living activities. Our results suggest that the CSF can be used as a diagnostic tool to analyze visual function associated with deficits in functional independence after stroke. These findings should be considered across the continuum of care for these patients.

Figure 1

Example of a pair of stimuli. On the left, a sine-wave grating with the spatial frequency of 0.6 cpd, and on the right, a neutral stimulus. The stimuli were originally calibrated for viewing at a distance of 150 cm.

Figure 2

Contrast sensitivity to sine-wave gratings. Contrast Sensitivity Curves for Spatial Frequencies of Patients with Functional Independence, according to the Barthel Index, from 20–35 (2A), 40–55 (2B), 60–95 (2C) and 100 points (2D). The letter “n” represents the number of curves measured for each sub-group. The vertical lines show the standard error of the mean for each frequency (0.6, 2.5 and 10.0 cpd).