by Deborah Zelinsky, OD, FNORA, FCOVD
The eyes provide a direct connection to the brain — because the retina is made from brain tissue. When light strikes the neural portion of the retina, it activates brain function in a point-to-point representational map.
This connection between a visual stimulus (light) and the neural tissue is integral not only to eyesight, but also to the regulation of many other physical functions, including posture, sleep and blood pressure.
Anyone who has ever tried on someone else’s glasses understands intuitively that the wrong prescription can make you feel bad internally (ie, dizzy or nauseous). But it is much less well understood that the right prescription can make you feel better internally. This type of prescription relies on the activation of the hypothalamus via the retino-hypothalamic tract and the brainstem via the retino-collicular pathway
For example, I saw a patient with a functional midline shift who was continually straining his neck muscles. Weekly chiropractor visits provided relief, but within a few days his neck and shoulders hurt again. By prescribing glasses with a little blur in the nondominant eye, the patient reflexively shifted his head position and relaxed his neck muscles, while fixating his dominant eye more accurately because the peripheral signals of the two eyes helped him efficiently localize the target.
I have also seen patients with imbalanced cylinder axes. When each eye is refracted separately behind a phoropter, the measured axis might be 20° in one eye and 180° in the other, but this leads to a shift in the lower back that can be quite uncomfortable. Patients with imbalanced axes sometimes find that crossing their legs improves comfort, but in some situations — sitting at a desk in school, for example — the legs can’t easily be crossed. Children end up using cognitive reserves just to compensate for the discomfort, leading to attention and short-term memory problems. We can address that by balancing out the cylinder axes so that they add to 180° (or are each 180°).
There is much more to correcting visual processing than just sharpening central eyesight. Consider that according to Patrick Quaid, MCOptom, FCOVD, PhD, approximately 6% of the visual field is dedicated to central targets, while the remaining 94% is for peripheral retinal processing. We use our central eyesight for stationary targets (like an eye chart or a book), but seeing moving targets is highly dependent on peripheral eyesight. Moving targets are found all around our environment, including on screens used in GPS navigation systems or website scrolling. We use peripheral and central eyesight as a team to scan and shift gaze from place to place, such as from a dashboard to the road when driving, or from a desk to a teacher or from a tennis ball to a player.