Duration of Binocular Decorrelation Predicts the Severity of Latent (Fusion Maldevelopment) Nystagmus in Strabismic Macaque Monkeys
Michael David Richards 1,
Agnes Wong 2,
Paul Foeller 3,
Dolores V. Bradley 4,
and
Lawrence Tychsen 5*
1 Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, Canada
2 Departments of Ophthalmology and Vision Sciences, University of Toronto, Toronto, Canada; Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri, United States
3 Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri, United States
4 Yerkes Regional Primate Research Ctr, Division of Visual Science, Atlanta, Georgia, United States
5 Ophthalmology & Visual Sciences, Washington University School of Medicine, St. Louis Children's Hospital, St. Louis, Missouri, 63110, United States; Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri, United States
* To whom correspondence should be addressed. E-mail: stockstad{at}vision.wustl.edu.
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Abstract |
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Purpose: Infantile esotropia is linked strongly to latent fixation nystagmus (LN) in human infants, but many features of this co-morbidity are unknown. The purpose of this study was to determine how the duration of early-onset strabismus (or timeliness of repair) affects the prevalence of LN in a primate model.
Methods: Optical strabismus was created in infant macaques by fitting them with prism goggles on day 1 of life. The goggles were removed after 3 weeks (n=2),12 weeks (n=1) or 24 weeks (n=3), emulating surgical repair of strabismus in humans at 3, 12, and 24 months of age, respectively. Eye movements were recorded using binocular search coils.
Results: Each animal in the 12- and 24-week groups exhibited LN and manifest LN, had normal spatial vision (no amblyopia) and a constant esotropia. The 3-week duration monkeys had stable fixation (no LN) and normal alignment indistinguishable from control animals. In affected monkeys, the longer the duration of binocular decorrelation, the greater the LN: mean slow-phase eye velocity (SPEV) in the 24 week animals was 3 times greater than that in the 12-week monkey (p = 0.03); mean LN intensity in the 24-week monkeys was 3 times greater than that in the 12-week (p = 0.03).
Conclusions: Binocular decorrelation in primates during an early period of fusion development causes permanent gaze instability when the duration exceeds the equivalent of 3 months in human. These findings support the conclusion that early correction of infantile strabismus promotes normal development of cerebral gaze-holding pathways.
Key Words:
infantile esotropia, latent nystagmus, binocularity
