Why Do the Eyes Get Tired?
We’re all familiar with the feeling of tired eyes at bedtime, right before falling asleep. The eyelids feel heavy and they begin to droop. Your field of vision narrows as you squint and blink at the TV screen, trying to stay awake. Then your eyelids become even heavier and close when the need for sleep takes over. It is also common to have tired eyes at the end of a long day or after many hours of concentration during which you must keep your eyes open. But why is it, exactly, that the eyes get tired at all? What is it that makes them feel so heavy and irritated? The answers to those questions require a thorough examination of the anatomy of the eye itself.
Imagine flexing the muscles in your arm to hold a relatively light weight, like an average sized book, for example, away from your body at chest level. Initially you may hardly feel the weight and it requires virtually no effort to hold the book while performing other tasks. Over time, however, as the muscle starts to fatigue, you may start to experience a nagging ache or soreness. Eventually your arm may begin to shake and twitch and a weight that once required virtually no effort at all now becomes almost impossible to bear.
The process that results in eye fatigue follows a similar course. While the entire back of the eye is covered with light sensitive photoreceptors, the color-sensitive cones are most densely concentrated at the fovea centralis, a small pit located in the center of the retina. This tiny area is responsible for the sharp central vision (also called foveal vision) necessary for activities where visual detail is of primary importance, such as reading and driving. When concentrating on an image, the six distinct muscles surrounding each eye work constantly, making tiny adjustments that keep the fovea lined up perfectly with the target. The eye muscles are actually 100 times stronger than they need to be to perform their function, so the initial strain is completely unnoticeable. However, as time goes on, tension mounts and what was once effortless becomes increasingly difficult.
Moreover, eye fatigue can be further exacerbated by dryness. People ordinarily blink about 12 to 17 times every minute, spreading oils and mucus secretions across the surface of the eyes in order to keep them clean and moist. However during periods of intense focus, and most particularly when gazing for long periods at a computer monitor, the blink rate slows to as little as four to five blinks per minute. Without constant lubrication, the eyes start to dry out and become irritated, giving them that characteristic sand-paper feel. The effect of computer use on eye strain has become so prevalent (affecting an estimated 150 to 200 million Americans) that Computer Vision Syndrome is considered one of the most wide-spread workplace ergonomic issues today.
Fortunately, eye fatigue can usually be treated just like any other form of muscle fatigue, with rest. The muscles responsible for eye movement are remarkably resilient, so even relatively short breaks, taken at regular intervals throughout the day, can have a positive effect. Try the 20-20-20 rule: every 20 minutes, look away about 20 feet in front of you for 20 seconds, and remind yourself to blink frequently. Struggling to focus with refractive vision errors, like hyperopia and astigmatism, can also over-stress the eyes, so frequent and persistent cases of eye fatigue may be an indication that you may have another vision problem. Undergoing regular comprehensive eye examinations can be the best way to keep your vision healthy and sharp and to catch and treat possible problems before they become serious.
If you have any questions about problems you may be having with your vision, or would like to schedule an eye exam, please contact Georgia Eye Physicians and Surgeons today to make an appointment. Be sure to follow us on Facebook, Twitter, and Google+ for more information on how to keep your vision healthy.