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Asthenopia (aesthenopia) from the Greek word "asthen-opia : ασθεν-ωπία" or eye strain is an ophthalmological condition that manifests itself 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 display uses PWM for dimming. This causes the backlight to turn on and off at slower 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 as in this image) 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.
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 the viewing of monitors such as those of computers or phones.
While preventive measures, such as taking breaks from activities that cause eye strain are suggested, there are certain treatments which a person suffering from the condition can take to ease the pain or discomfort that the affliction causes. Perhaps the most effective of these is to remove all light sources from a room, and allow the eyes to relax in darkness. Free of needing to focus, the eyes will naturally relax over time, and relieve the discomfort that comes with the strain. Cool compresses also help to some degree, though care should be taken to not use anything cool enough (such as ice) to damage the eyes themselves. A number of companies have released "computer glasses" which, through the use of specially tinted lenses, help alleviate many of the factors which cause eye strain, though they do not completely prevent it. Rather, they just make it harder to strain the eye.
- Computer vision syndrome
- Eye examination
- Vision therapy
- Visual looming syndrome
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