Take a look at this article on Impaired Body Balance Control in Adults with Strabismus. Last week my colleagues and I who render the Expert Opinions at Elsevier’s Practice Update for Eye Care decided to make this our feature article. So I got together with the pediatric ophthalmologist at our local OMNI Eye Center, Joseph D. Napolitano, M.D. and put together this commentary on the article.
It was once believed that a critical period existed for the development of binocular vision, and that intervention to develop binocular vision after this critical period was futile. This led to the drive toward strabismus surgery at a very young age, and a tendency to advise patients that treatment for strabismus beyond childhood was pointless. Evidence continues to mount that this view is outdated, owing to the ability of the brain to reorganize itself. The general term for this ability is neuroplasticity, and research in vision science has produced a massive body of literature on perceptual learning in the successful treatment of amblyopia into adulthood.
Although alignment of the eyes in infantile strabismus can be achieved in many instances through early intervention, are there deficits that persist into adulthood despite the appearance of straight eyes? The article by Przekoracka-Krawczyk, Nawrot, Czainska, and Michalak adds to a growing body of literature that strabismus is a head-to-toe problem that results in impairments and adaptive compromises at multiple levels throughout the body. Through posturography they demonstrate that inaccurate signals related to extra-ocular muscles have a strong impact on body balance, and that this effect can be observed even into adulthood. The second part of their study shows that specific mental tasks can enable adult subjects with strabismus to develop postural compensatory mechanisms for better body balance.
The authors postulate that cerebellar dysfunction may contribute to strabismus. The cerebellum plays an important role in eye movement coordination and alignment. The cerebellum is also responsible for the integration of signals coming from basal ganglia with signals from the vestibular nucleus and motor cortex that help control limb position as well as stable posture. While the cerebellum has long been recognized for its role in motor control, recent studies have shown the extent to which it is also involved in cognitive functions including attention. This led the authors to theorize that attentional effort required for the mental task in their study resulted in arousal and activation of the cerebellum that decreased inhibition from the strabismic eye. This disinhibition is iinked to greater postural control.
Why is this research exciting? It counteracts the notion that strabismus is an isolated eye muscle problem that has little bearing other than cosmesis. The appearance of the eyes is only one feature of strabismus, better appreciated as a difficulty in mutlimodal coordination. This presents new opportunities to conceive of the synergy between extra ocular muscle surgery and optometric vision therapy, somewhat analogous to the synergy between orthopedic surgery and physical therapy.
When conceived in this fashion, the cognitive and attentional resources employed in optometric vision therapy help the brain to coordinate both eyes through activities mediated through the cerebellum. Even when EOM surgery or optometric vision therapy do not achieve bi-foveal alignment or random dot stereopsis, very meaningful gains can be realized in improved head to toe motor control.