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Early versus delayed repair of infantile strabismus in macaque monkeys: I. ocular motor effects
Agnes M F Wong1, Paul Foeller, Dolores Bradley
1Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri, USA.
Insights
Early surgical correction of infantile esotropia in primates prevents abnormal eye movement development. Delayed correction leads to persistent strabismus and severe visual motor pathway maldevelopment.
Area of Science:
- Neuroscience
- Ophthalmology
- Developmental Biology
Background:
- Infantile esotropia is associated with abnormal visual motor pathways.
- The optimal age for surgical correction remains debated.
- Early intervention may impact brain development.
Purpose of the Study:
- To investigate the influence of early versus delayed strabismus correction on visual motor pathway development.
- To compare outcomes in primates with experimentally induced and naturally occurring esotropia.
Main Methods:
- Infant macaques were fitted with prism goggles to induce optical strabismus.
- Groups experienced early (3 weeks) or delayed (3-6 months) correction.
- Eye movements (fixation, smooth pursuit, OKN) were recorded post-correction.
Main Results:
- Early correction resulted in normal eye movements and alignment, indistinguishable from controls.
- Delayed correction led to persistent esotropia, nystagmus, and pursuit/OKN asymmetry.
- Longer delays correlated with more severe, adult-like abnormalities.
Conclusions:
- Early strabismus correction in primates prevents visual motor pathway maldevelopment.
- Findings support the benefit of early surgical intervention for infant brain development.
Introduction:
The appropriate age for surgical correction of esotropic strabismus in human infants is controversial; some clinicians advocate surgery before age 6 months, and others recommend observation and surgery at older ages. Infantile (congenital) esotropia in humans and monkeys is known to be accompanied by a constellation of eye movement abnormalities caused by maldevelopment of cerebral visual motor pathways. The purpose of this study was to determine how early versus delayed correction of strabismus influences development and/or maldevelopment of these eye movement pathways.
Methods:
Optical strabismus was created in infant macaques by fitting them with prism goggles on day 1 of life. The early correction group (2 experimental and 1 control) wore the goggles for a period of 3 weeks (the equivalent of 3 months before surgical repair in humans). The delayed correction group (3 experimental and 1 control) wore the goggles for a period of 3 or 6 months (the equivalent of 12 or 24 months before surgical repair in humans). Several months after the goggles were removed, the monkeys were trained to perform visual fixation, smooth pursuit, and optokinetic nystagmus (OKN) tasks for a juice reward. Eye movements were recorded using binocular search coils. The performance of the early versus delayed infant monkey groups was also compared with that of a group of adult monkeys who had unrepaired, naturally occurring infantile esotropia.
Results:
Early correction monkeys developed normal eye movements and exhibited ocular motor behaviors that were indistinguishable from normal control animals. They regained normal binocular eye alignment and showed stable fixation (no latent nystagmus). Monocular horizontal smooth pursuit and large field OKN were symmetric. In contrast, delayed correction monkeys showed persistent esotropia, latent fixation nystagmus, dissociated vertical deviation, and pursuit/OKN asymmetry. Animals who had the longest delay in correction of the optical strabismus exhibited eye movement abnormalities as severe as those of adult animals with uncorrected, natural esotropia.
Conclusions:
Early correction of strabismus in primates prevents maldevelopment of eye movements driven by cerebral motor pathways. Our results provide additional evidence that early strabismus correction may be beneficial for brain development in human infants.
