August 16, 2006
By Dr. David Eilbert
A very commonly overlooked cause of vision problems arises from eye muscle coordination. Each eye has six muscles that control vertical, horizontal, converging and rotational movements, and they all work together so that both eyes line up on the same target.
To give you an idea of the importance our bodies place on eye muscle coordination: there are 12 cranial nerves (nerves that run directly from the brainstem to specific organs or regions), one each to control such "trivial" functions as sight, smell, hearing, breathing, heart rate . . . three of these 12 are devoted to these six pairs of muscles!
In addition to the critical neural coordination, the muscles themselves must be positioned properly to have comfortable vision. When the muscles are in their rest position, the eyes should be perfectly aligned. Usually, however, they are not quite perfect. The muscles then have to work a bit to get the proper binocular vision. This extremely common condition is called phoria. If not, double vision would result.
A small degree is most often easy to compensate for. Larger amounts will produce strain and tiring, and possibly double vision. If the deviation is large enough, the brain will "surrender," and one eye will turn (called strabismus). An important note: this rest position is pretty much the same throughout an individual's life. What changes is muscle strength and, of course, vision requirements (college, job demands, etc). When someone is born with strabismus, the brain has a choice of seeing double, or blocking the vision in that eye. The choice is almost always to block, or suppress, the vision in one eye.
The main problem with this is that the eye remains unused, and, like any body part that is unused, weakens. This is called lazy eye, or Amblyopia. Interestingly, there is less eyestrain caused by strabismus than by significant phoria, because in phorias, the eyes are working constantly to maintain binocular vision. Remember this difference: phoria means that the muscles are aligning with strain; strabismus means that the eyes are not aligned, and don't even attempt to align.
Another variety of muscle imbalance is caused by focusing of the eye. When the lens of the eye focus to see close objects, a message is sent to the eye muscles to converge, forming a "V" at that close object. Sometimes, the amount of convergence sent is more than necessary; the eyes have converged too much, causing accommodative ("focusing") phoria or even strabismus.
How do we treat eye muscle imbalances? When there is a moderate to large phoria, eye muscle exercises can be very valuable. Just like exercising any other muscle in the body, these muscles can be strengthened to alleviate symptoms. Very often, eyeglasses can be made to reduce the total effect of the phoria. I usually include a correction called prism, which shifts images in the direction your eye muscles are trying to relax to. In the case of accommodative phoria, reading glasses to help reduce the focusing of the lens of the eye will work great.
In cases of strabismus and very large phorias, surgery (extraocular muscle surgery) should be considered a viable option. This surgery is far more effective at a younger age, before ambyopia becomes an issue. However, there are cases where I recommend surgery for adults as well.
If you suffer from frequent headaches, rapid tiring while reading or any detail work, or double vision, your binocular vision should be evaluated. If you suspect that your child has an eye turn, he or she should be evaluated for this at the earliest possible age.
Dr. David Eilbert, Optometrist
North Fork Optical Center
PO Box 1419
Mattituck Center, Main Rd
Mattituck, New York 11952