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• Having to read or use a computer at a fixed, set distance for a long continuous
  period of time. Even if a person has more than adequate focusing ability, focusing at
  a set distance continuously can fatigue the lens.
  
• Having to read or work at very close distances. This requires much more focusing
  and leads to more rapid fatigue.
  
• Using inadequately powered reading glasses, or using an outdated glasses
  prescription.
• Working in situations with inadequate lighting, or with glare from overhead lighting.
  
• Having other underlying eye problems, such as ocular allergy or dry eye.
  
• Having an imbalance in eye muscle alignment, so that the eyes have to fight to stay
  fixated on a near object.
  

What Can We Do About Eyestrain?
Eyestrain will not permanently damage the eyes or cause a loss of vision. However, it can
be very uncomfortable and lead to a loss of productivity. Anyone who uses a computer
can take measures to reduce eye discomfort.

Get An Eye Exam
The American Academy of Ophthalmology suggests that you start with a comprehensive
eye exam. This is always a good staring point anytime you experience symptoms like
headaches, eye strain, blurred vision, eye irritation, double vision, excessive tears, dry
eyes, pain in the eyes, excessive blinking or squinting. The exam will help rule out any
ocular conditions that may exist that are causing eye symptoms.

Vision Correction
Getting an eye exam is especially important if you wear glasses or contact lenses. Let the
ophthalmologist know how often you are in front of a computer screen. Since most
glasses are made to correct for a reading distance of 16 inches, it is important that they
are adjusted for your particular work environment. It is recommended that the computer
screen should be 20 to 26 inches from your eyes, and your glasses can be made to
accommodate this distance. Your glasses can also receive special anti-reflective coatings
and tints to help reduce eyestrain. If you are over forty, you may require one pair of
glasses that corrects for your “normal” prescription and another pair that corrects your
vision when in front of a computer screen. If you are over forty and require reading
glasses or wear bifocals (with lines or without), the need for two separate pairs of glasses
may be even more necessary.

If you do not normally require a vision correction, computer eyeglasses with low power
plus lenses and sometimes a light tint is often helpful. The color of the tint depends upon
the screen background color, ambient room lighting, and your prescription. This should
be discussed with the optician.

Adjust The Equipment
Set the monitor, desk, and chair at comfortable distances and heights. Some of these
figures may be obtained in the documentation that came with the computer products.
Most users prefer a viewing distance of 20 to 26 inches, but this distance should be
between 18 and 28 inches; a little farther away than for reading printed text. The computer
screen should be placed slightly below eye level. A good rule of thumb is that the center
of the computer screen should be 4 to 9 inches below your eyes, enabling you to look
down slightly at your work. Adjust the brightness of the monitor to an intensity that is
comfortable to your eyes; not to bright and not to dim. Then adjust the contrast control so
that the characters on the monitor and the background so the letters are easily read.

Create Good Lighting And Reduce Glare
Try to modify the lighting eliminating glare and harsh reflections. If reading, having the
light source coming from behind, over your shoulder, helps to prevent glare problems. If
using a computer, dark print on a white or light gray background is less fatiguing to the
eyes than multicolored print. Sometimes a plastic or glass filter over a computer screen
with an anti-reflective coating can help with computer glare. These can be purchased from
any office supply store.

Rest Your Eyes Periodically
Take frequent, short breaks from near work by focusing on a distance object for a few
seconds. Every twenty minutes, get up, stretch your back and neck and look around.
Move your eyes and move your body, change your position.

Change the distance that you work frequently. If the eyes are feeling increasingly fatigued,
hold things further away rather than closer to you. Avoid getting very close to what you
are reading.

Avoid Dry Eyes
Blink! Studies have shown that when you look at the computer monitor, there is a natural
tendency toward a reduced blink rate. The less you blink, the more likely you are to
experience dry eye symptoms of burning, sand-in-the-eye, heavy lids, etc.

The normal blink rate is averages 12 times per minute. Computer users usually blink 5
times per minute. The longer the eye remains open between blinks, the more likely the
cornea is to dehydrate, burn or ache. Then, finally, you blink. But the damage, although
minor and easily repaired, is already done. Your eyes sting, burn, sting and otherwise feel
miserable. You tear, feel better, then start the process all over again. Eventually, the
disruption to the corneal tissue causes a blurred image to go along with the other
symptoms. You stop work, fall asleep and your body heals itself until the next time.

There are plenty of non-prescription tear replacement or rewetting drops available at your
local drug store but being aware of the need to blink is the real fix, especially if you wear
contact lenses.

Article extracted from : http://www.pasadenaeye.com/faq/faq08/faq08_text.html