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Mariline Pageau, Danielle de Guise, Dave Saint-Amour; Comparison of local and global stereopsis in children with microstrabismus. Journal of Vision 2009;9(8):284. doi: 10.1167/9.8.284.
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Introduction: Convergent strabismus is a common condition in children which has been divided into several categories including microstrabismus. The main features of microstrabismus are small unilateral deviation of the eye (between 0° and 5°), strabismic and/or refractive amblyopia, foveal suppression, and an abnormal retinal correspondence. It is generally accepted that stereopsis is present in patients with microstrabismus, although it is reduced. However, this concept relies primarily on the evaluation of local stereopsis, which contains visible local indices and monocular cues. Global stereopsis lacks monocular cues and is therefore crucial to precisely determine the ability of a patient to perceive depth.
Methods: A sample of 17 children (6 to 14 years of age) with microstrabismus was selected at the Clinique Universitaire de la Vision of University of Montreal. All 17 children were diagnosed with microstrabismus. Their local and global stereoscopic thresholds were obtained using the Randot® test.
Results: Ten children with microstrabismus (10/17, 59%) had local stereopsis of 50 seconds of arc or worst (standard being 20 seconds). A complete lack of stereopsis was observed in 7 (41%) children. Interestingly, none of the children tested was able to perceive global stereopsis with the exception of one child during only one of the follow up visits.
Conclusion: This study shows the relevance of testing both local and global stereopsis to assess the integrity of binocular vision. Many patients with microstrabismus show some degree of depth perception but only when measured with local stereopsis. Normal stereoscopic vision implies also the ability to discriminate random dot stereograms. A measurement of global stereoscopic threshold should therefore be performed with all patients in order to acquire a much more reliable estimate of their level of stereoscopic vision.
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