[Local and global stereopsis in children with microstrabismus]

Introduction: It is generally accepted that stereopsis is present in patients with microstrabismus, although it is reduced. This concept relies primarily on the evaluation of local stereopsis, which contains visible monocular cues. However, microstrabismic patients seem to present much more impairment in identifying the global form in random dot stereograms (global stereopsis). The present study aims to verify the hypothesis that local stereopsis is superior to global stereopsis in children with microstrabismus.

Method: In this retrospective study, a sample of 26 children (6 to 14 years of age) with microstrabismus was selected at the Clinique Universitaire de la Vision of the University of Montreal. Their local (visible contours) and global (random dot stereograms) stereoscopic thresholds were obtained using the Randot Stereotest(®).

Results: Normal, or slightly inferior to normal, local stereoscopic threshold were found in nineteen microstrabismic children (19/26, 73%), some of them presenting up to 20 seconds of arc. A complete lack of local stereopsis was observed in 7 (27%) children. However, none of the children tested were able to perceive global stereopsis with the exception of one child.

Conclusion: Local stereoscopic vision is present, although altered, in microstrabismic children but global stereoscopic vision is generally absent.