Article

The many enigmas of intermittent exotropia

University of California, San Francisco, CA 94143, USA
The British journal of ophthalmology (Impact Factor: 2.81). 08/2012; 96(10):1280-2. DOI: 10.1136/bjophthalmol-2012-302345
Source: PubMed
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    ABSTRACT: PURPOSE: To investigate the effect of initial postoperative minimal overcorrection on the result of the surgical management of intermittent exotropia based on long-term follow-up results. METHODS: 111 patients who underwent surgery for intermittent exotropia and were followed up for at least 5 years after surgery were retrospectively reviewed. The outcome was judged to be successful when there was 10 prism dioptres (PD) or less of exodeviation and less than 5 PD of esodeviation without any reoperation at the final follow-up visit. We evaluated the success, recurrence, overcorrection rate and the duration of diplopia according to their initial deviation. RESULTS: We divided patients into four groups based on their initial deviation: orthophoria or undercorrection (Ortho group, 31 patients), minimally overcorrected at 5 PD or less (MO group, 20 patients), usually overcorrected between 6 PD and 10 PD (UO group, 35 patients), and highly overcorrected at more than 10 PD (HO group, 25 patients). The success rate was 43-60% between the four groups (p=0.52). The recurrence rate was 28-57% (p=0.105), but post hoc analysis showed borderline p values between the Ortho and HO group (p=0.024). No overcorrection was noted in the Ortho and MO groups (p=0.04). The duration of diplopia was 0-2.5 weeks, showing statistically significant difference among groups (p<0.001). CONCLUSIONS: The amount of initial postoperative overcorrection may not predict the long-term success rate. However, the MO group showed a lower recurrence rate than the Ortho group and also showed no overcorrection and a shorter duration of postoperative diplopia than the UO and HO groups.
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    ABSTRACT: In strabismus, potentially either eye can inform the brain about the location of a target so that an accurate saccade can be made. Sixteen human subjects with alternating exotropia were tested dichoptically while viewing stimuli on a tangent screen. Each trial began with a fixation cross visible to only one eye. After the subject fixated the cross, a peripheral target visible to only one eye flashed briefly. The subject's task was to look at it. As a rule, the eye to which the target was presented was the eye that acquired the target. However, when stimuli were presented in the far nasal visual field, subjects occasionally performed a "crossover" saccade by placing the other eye on the target. This strategy avoided the need to make a large adducting saccade. In such cases, information about target location was obtained by one eye and used to program a saccade for the other eye, with a corresponding latency increase. In 10/16 subjects, targets were presented on some trials to both eyes. Binocular sensory maps were also compiled to delineate the portions of the visual scene perceived with each eye. These maps were compared with subjects' pattern of eye choice for target acquisition. There was a correspondence between suppression scotoma maps and the eye used to acquire peripheral targets. In other words, targets were fixated by the eye used to perceive them. These studies reveal how patients with alternating strabismus, despite eye misalignment, manage to localize and capture visual targets in their environment.
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