We finished Part 1 by citing a recent editorial from Dr. Paul Romano, an ophthalmologist and editor of Binocular Vision & Strabismus Quarterly. One of the fundamental disconnects between what most general and pediatric ophthalmologists know about optometric vision therapy, even if limited it to “binocular vision alignment”, is encapsulated in the artificial distinction between eyes and brain. This was made very clear in a policy paper adopted by the American Optometric Association on vision as a collaboration between the eyes and the brain. My hunch is that neuro-ophthalmologists intuitively understand this. This book edited by two world-renowned authorities in ophthalmic neurology provides a bit more insight into the scientific underpinnings of vision therapy and rehabilitation.
Consider the following information from Dr. Richard Abadi in his chapter on Perception with Unstable Fixation:
The fixation system has three distinct components:
1) The visual system’s ability to detect retinal image drift and program corrective eye movements.
2) The ability to attend to or “engage” a particular target of interest.
3) The suppression of unwanted saccades that would otherwise take the eye off target.
During locomotion the vestibulo-ocular and optokinetic systems act in unison to reduce retinal-image slip. Thus gaze-holding has both visual (smooth pursuit and optokinetic) and motor (vestibular) inputs that are underpinned by neuronal processes (fixation cells in the superior colliculus, pause cells in the brainstem, and the neural integrators in the brainstem and cerebellum). The desired outcome of steady fixation is also dependent on critical cognitive factors such as attention, alertness, and the saliency of the visual task.
Consider as well the following information from Larry Abel and Linda Malesic in their chapter on Internal and External Influences on Foveation and Perception in Infantile Nystagmus Syndrome:
Changes with arousal level or emotional states suggest inputs from areas of the brain that are not usually incorporated into ocular motor models. When patients with ocular motor difficulties exert more visual effort to engage in active viewing, ocular motor instabilities can increase. In other words, the “effort to see” in conditions such as infantile nystagmus syndrome can make vision worse under conditions of considerable personal importance – for example, when trying to pass a driver’s license vision test or get through school examinations. The act of trying to achieve a highly desired goal can be a potent stressor. Although mechanisms that give rise to oscillations of fixation may be centered in the brainstem, they are under the influence of other regions of the CNS, apparently including cortical and subcortical regions that underlie such higher cognitive functions as top-down allocation of attention and limbic system processes such as the stress response. Perception in some patients with these conditions is susceptible to destabilization under the influence of these processes.
Before proceeding I want to emphasize how important the lead statement in the section above is, so I’ll bold it for emphasis: Changes with arousal level or emotional states suggest inputs from areas of the brain that are not usually incorporated into ocular motor models.