Computer Vision Syndrome
Presbyopia and Dry Eye

The problem with general purpose eyewear at the computer

The most common method for prescribing and designing bifocals is to prescribe a lens add to provide clear vision at 40 cm (16 inches) and the flat top bifocal is fitted to enable near vision with a downward gaze angle greater than about 25 degrees. However, the computer screen is usually further away (50-70 cm, or 20-28 inches) and only 10-20 degrees downward. A presbyope who tries to wear their �usual� bifocal correction at the computer will either not see the computer screen clearly or will need to assume an awkward posture. Most commonly they move closer to the screen and tilt their head backwards - resulting in neck and back strain.

 

General wear progressive addition lenses also do not work well at the computer. Even though progressive addition lenses provide a region with an intermediate add, this is the portion of the lens with the narrowest field of clear vision. The person must continually find the small �sweet� spot on the lens and use their neck to move their head rather than moving their eyes when changing fixation.

Early presbyopes with low adds can often use their general wear glasses at the computer � because they can use their remaining accommodation to see at intermediate distances thereby allowing them to use the distance portion of their bifocal or progressive lens. Also, if the person only works intermittently at the computer, they can tolerate awkward posture for short periods of time.

Other than the 2 exceptions noted above, most patients who require bifocals or progressive addition lenses for normal visual tasks require a separate pair of spectacles for their computer work.