Eyestrain complaints are typically reported by three of four people who use computers for extended periods. One researcher has estimated that each year about 10 million people seek eye exams for computer-related eyestrain. People often experience vision deficits that become more pronounced with demanding visual tasks.

Common problems include:

Reduced close focusing related to aging, known as presbyopia.
Insufficient focusing speed.
Binocular insufficiency (eyes do not track well together.)
Farsightedness (the ability to focus well on distant objects but poorly on close objects).

When estimating appropriate lighting levels, consider the task types to be performed at the computer.

Low ambient light levels may be acceptable with jobs that are screen-intensive (e.g., desktop publishing).
On the other hand, data input tasks will likely be improved with somewhat higher ambient light levels, especially if the source document characters are small or are of low-contrast.
Computer monitors should be set at right angles to windows and to long runs of overhead fixtures.
The orientation depicted at right reduces screen glare and eliminates bright light directly striking the eye.
If reducing light levels and changing monitor orientation has not sufficiently reduced screen glare, an anti-glare screen may be warranted.
A quick way to check for screen glare is to sit at your computer with the monitor off. Glare problems will become apparent.

Low light levels are best for work at computers, yet we need relatively high light levels to read books and papers.

To solve this problem, it’s best to reduce light from overhead sources and add adjustable task lighting to illuminate paperwork.
The task light should be constructed and oriented to avoid screen glare and/or direct light into the eye.

Viewing close objects causes the focusing and convergence muscles in the eyes to work harder.

Moving your monitor back may reduce eyestrain (a distance of 20” - 26” is suggested).
Lowering your monitor may also reduce computer-related eyestrain.
Placing your monitor directly on the desk top is recommended (not on top of the computer/CPU).
If you reference source documents frequently, document/monitor orientation may influence eyestrain symptoms.
Documents are best oriented horizontally with respect to the monitor.
Vertical orientation is nearly as good as horizontal.
“Slant boards” may also improve posture when document viewing and marking is required.