The influence of adaptation on visual motion detection in chronic sixth nerve palsy after treatment with botulinum toxin.
ABSTRACT To investigate changes in visual motion perception after treatment with botulinum toxin in patients with unilateral chronic lateral rectus muscle palsy.
Five patients and control subjects were asked to report the perceived drift direction of a sinusoidal grating that was initially stationary and then began to accelerate at 0.09 degrees /sec2 in a horizontal direction. The grating had a field size of 18.5 degrees and was presented monocularly with a contrast just above threshold for visibility for central vision. Both the paretic and non-affected eyes were tested. Psychophysical testing was performed under the following conditions: 1) before treatment and testing, patients occluded their paretic eye for at least three days to avoid diplopia. 2) After treatment with botulinum toxin, alignment was corrected and patients stopped occluding their paretic eye for at least three days before testing. The control subjects occluded their non-dominant eye for three days before testing.
In condition 1, no differences in motion detection values between patients and control subjects were found. In condition 2, motion detection thresholds were raised approximately 0.15 degrees /sec as compared to pre-treatment values and compared to the control group.
After treatment, a raised threshold for motion detection is one mechanism used to avoid oscillopsia and visuo-vestibular disorientation during head movements in patients with chronic paralytic squint. This study lends evidence that perceptual-adaptive, compensatory mechanisms develop to reduce oscillopsia and disorientation rather than being caused by abnormal cortical motion processing or defective eye muscle action.
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ABSTRACT: Labyrinthine defective subjects (LDS) experience oscillopsia during head movements due to the absence of the vestibulo-ocular reflex (VOR). The purpose of this study was to compare horizontal and vertical visual motion detection in LDS during (i) body-stationary and (ii) horizontal whole-body oscillation conditions. Twelve LDS and controls detected the onset of drift direction of a grating that moved with accelerating velocity. Thresholds were raised in the patient group in both conditions. The loss of the VOR per se cannot explain raised thresholds in the body-stationary condition nor during whole-body (horizontal) oscillation with vertical grating motion. Findings indicate changes in visual processing that make LDS less sensitive to visual motion. It is postulated that these changes are due to adaptive mechanisms involved to reduce oscillopsia.Vision Research 07/2003; 43(14):1589-94. · 2.14 Impact Factor
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ABSTRACT: This study tested the hypothesis that elementary visuo-motor functions involved in visual scanning, as measured by fixation and saccadic tasks, are better in a group of high-level clay target shooters (N=7) than in a control group (N=8). In the fixation task, subject were told to keep fixation as still as possible on a target for 1 min, both in the presence and absence of distracters. For shooters, time did not have an effect on fixation stability, and they had more stable fixation than controls in the distracters condition. Results indicate a difference between groups on both the temporal span of attention and selective attention. In the saccadic task, subjects were asked to saccade, as fast as possible, towards a peripherally displayed target. Two conditions were used: simple reaction to target onset and discrimination between targets and distracters. Shooters had faster saccadic latency to targets than controls in both conditions. Finally, to evaluate the effect of exercise on saccadic latency, we trained one control subject to saccade to a target displayed at a constant spatial position. At the end of the training, saccadic latency reached a value comparable to that recorded in shooters. Learning was largely retinotopic, not showing transfer to untrained spatial positions.Vision Research 09/2003; 43(17):1837-45. · 2.14 Impact Factor
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ABSTRACT: To test the hypothesis that in patients with acquired chronic bilateral ophthalmoplegia, abnormal retinal image slippage during head movements would result in abnormal thresholds for visual perception of motion. Five patients (two males and three females) with ophthalmoplegia were included in the study. The average age was 44 years (range 30-69 years). The aetiology of ophthalmoplegia was myasthenia gravis (MG; n=2), chronic progressive external ophthalmoplegia (CPEO; n=2), and chronic idiopathic orbital inflammation. Visual motion detection thresholds were assessed using horizontal and vertical gratings (spatial frequency) set at thresholds for visibility. The grating was then accelerated at 0.09 deg/s(2). The subject's task was to detect the drift direction of the stimulus. Visual motion detection thresholds were raised to a mean of 0.434 deg/s (SD 0.09) (mean normal value 0.287 deg/s (SD 0.08)) for horizontal motion; and to a mean of 0.425 deg/s (SD 0.1) (mean normal value 0.252 deg/s (SD 0.08)) for vertical motion. The difference in values for both horizontal and vertical motion detection were statistically significant when compared with age matched controls; p <0.023 for horizontal motion and p<0.07 for vertical motion (two tailed t test). Abnormally raised visual motion thresholds were found in patients with ophthalmoplegia. This may represent a centrally mediated adaptive mechanism to ignore excessive retinal slip and thus avoid oscillopsia during head movements.British Journal of Ophthalmology 12/2001; 85(12):1447-9. · 2.73 Impact Factor