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Visual contrast sensitivity in tonic-clonic epileptic patients

Author(s): Paloma C. Bezerra | Caroline C. G. Alencar | Sandra R. Mousinho | Natanael A. dos Santos1

Journal: Psychology & Neuroscience
ISSN 1984-3054

Volume: 4;
Issue: 1;
Start page: 75;
Date: 2011;
Original page

Keywords: epilepsy | tonic-clonic seizures | contrast sensitivity | visual pathways.

We measured the effects of epilepsy on visual contrast sensitivity to linear and vertical sine-wave gratings. Sixteen female adults, aged 21 to 50 years, comprised the sample in this study, including eight adults with generalized tonic-clonic seizure-type epilepsy and eight age-matched controls without epilepsy. Contrast threshold was measured using a temporal two-alternative forced-choice binocular psychophysical method at a distance of 150 cm from the stimuli, with a mean luminance of 40.1 cd/m2. A one-way analysis of variance (ANOVA) applied to the linear contrast threshold showed signifcant differences between groups (F[3,188] = 14.829; p < .05). Adults with epilepsy had higher contrast thresholds (1.45, 1.04, and 1.18 times for frequencies of 0.25, 2.0, and 8.0 cycles per degree of visual angle, respectively). The Tukey Honestly Signifcant Difference post hoc test showed signifcant differences (p < .05) for all of the tested spatial frequencies. The largest difference between groups was in the lowest spatial frequency. Therefore, epilepsy may cause more damage to the neural pathways that process low spatial frequencies. However, epilepsy probably alters both the magnocellular visual pathway, which processes low spatial frequencies, and the parvocellular visual pathway, which processes high spatial frequencies. The experimental group had lower visual contrast sensitivity to all tested spatial frequencies.
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