Eye strain, also known as asthenopia, is an eye condition that manifests through nonspecific symptoms such as fatigue, pain in or around the eyes, blurred vision, headache, and occasional double vision. Symptoms often occur after reading, computer work, or other close activities that involve tedious visual tasks.
When concentrating on a visually intense task, such as continuously focusing on a book or computer monitor, the ciliary muscle tightens. This can cause the eyes to get irritated and uncomfortable. Giving the eyes a chance to focus on a distant object at least once an hour usually alleviates the problem.
A CRT computer monitor with a low refresh rate (<70Hz) or a CRT television can cause similar problems because the image has a visible flicker. Aging CRTs also often go slightly out of focus, and this can cause eye strain. LCDs do not go out of focus but are also susceptible to flicker if the backlight for the LCD uses PWM for dimming. This causes the backlight to turn on and off for shorter intervals as the display becomes dimmer, creating noticeable flickering which causes eye fatigue.
A page or photograph with the same image twice slightly displaced (from a printing mishap, or a camera moving during the shot) can cause eye strain by the brain misinterpreting the image fault as diplopia and trying in vain to adjust the sideways movements of the two eyeballs to fuse the two images into one. The word is from Greek "asthen-opia: ?????-????" = "weak-eye-condition".
Eye strain can happen with a blurred image (including images deliberately partly blurred for censorship), due to the ciliary muscle tightening trying in vain to focus the blurring out.
Video Eye strain
Causes
Sometimes asthenopia can be due to specific visual problems--for example, uncorrected refraction errors or binocular vision problems such as accommodative insufficiency or heterophoria. It is often caused by forcing the eye to focus and interpret visual data on a small region for a prolonged period of time. This can be caused while reading a book, driving a vehicle, using a digital screen or any similar task which fatigue the eye muscles. The condition worsens due to the buildup of fatigue over an extended period of time.
Maps Eye strain
See also
- Computer vision syndrome
- Photophobia
- Eye examination
- Vision therapy
- Astigmatism
- Visual looming syndrome
References
External links
- Mayo Clinic entry on Eyestrain
Source of article : Wikipedia
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