Last Thursday, July 1, 2010 it was my pleasure to present to the 3rd year students in their Vision Therapy Course at my Alma Mater, Michigan College of Optometry. As a Clinical Professor at MCO, the topic assigned to me for this lecture was about an interesting neural adaptation (anomalous correspondence) that patients can acquire when faced with the visual confusion of a disruption in binocular vision known as strabismus. Strabismus, or eye teaming failure, is often recognized by parents or doctors when an infant or toddler has an eye that appears “crossed” or “turned-out”.
Strabismus occurs in nearly 1 in 25 children and typically is the result of faulty neural development of the human visual brain. There are many different forms of strabismus and as a result it is important for the “Doctors in training” to have the opportunity to experience some of the visual components to the strabismus puzzle.
As one might assume, the human brain is “wired” to function with the input from both eyes “streaming” together in a coherent fashion. For those of us who have normally functioning binocular vision we only know that the world looks “normal”! We do not see it as a construct of two visual inputs combined. Yet our visual brain has “software” that enables the signals from both eyes to merge together as a single unified construct when we have normal binocular vision.
To demonstrate this really impressive “visual software” I showed the students the “hole in the hand” demo. All anyone needs to do is take a paper towel tube and hold it up to one eye and at the same time place their other hand adjacent to the paper towel tube directly in front of the other eye about 3-4 inches away. With both eyes open, what you will see may surprise you! Those with normal binocular vision will see the object being viewed by the eye looking through the tube as if it is actually projected through the hand that is in front of the other eye. This “hole in the hand” is an example of the neural software of the visual brain that gives us the ability to see with both eyes working together.
The visual brain is the dominant sensory system and integrates with every other sensory system. Therefore, any loss of binocular vision function can have a dramatic impact on the quality of life of the child or adult. This can occur on many different levels as the individual is forced to cope with “re-writing” adaptive neural software or develop “stress-response” avoidance behaviors in an effort to maintain homeostasis and reduce confusion.
So why bother with showing future Doctors, who are dealing with the rigors of 20 credit hours graduate school this simple “hole in the hand”? First off, this lecture did expand into the difficult to grasp complexities of neural adaptations to binocular vision dysfunction. However, at the same time knowledge presented in a lecture or garnered from a book does not typically give the level of understanding that can be better gained through a personal experience.
The “hole in the hand” shows the elegance of our binocular vision “software”. Any disruption in this naturally acquired development of the visual brain (such as strabismus or other conditions) will result in sensory loss. Consequently the result of any sensory loss brings about an associated functional loss. In this unique demonstration, the “hole in the hand” may help our Doctors in training have a sense of empathy for their future patients. Possibly in this small way our future Doctors will garner a better understanding that binocular vision does really matter to the patient.
Dan L. Fortenbacher, O.D., FCOVD