front surface of the eye is covered with a tissue
which consists of many glands. These glands secrete
the tears that cover the eye surface and keep
the eye moist, which is necessary for normal eye
function. The tears help maintain the proper oxygen
balance of the external eye structures and to
keep the optical properties of the eye sharp.
The normal tear layer is cleaned off and refreshed
by the blinking action of the eyelids.
The blink reflex is one of the fastest reflexes
in the body and is present at birth. However,
our blink rate varies with different activities-
faster when we are very active, slower when we
are sedate or concentrating. Studies which have
measured the blink rate and tearing on computer
workers and noted that the blink rate dropped
very significantly during work at a computer compared
to before and after work. There was no significant
change in tearing. The data support the fact that
blink rate decreases during computer use, but
also show that other tasks can decrease the blink
Possible explanations for the decreased blink
rate include concentration on the task or a relatively
limited range of eye movements. Although both
book reading and computer work result in significantly
decreased blink rates, a difference between them
is that computer work usually requires a higher
gaze angle, resulting in an increased rate of
tear evaporation. Since the main route of tear
elimination is through evaporation and the amount
of evaporation roughly relates to eye opening,
the higher gaze angle when viewing a computer
screen results in faster tear loss. It is also
likely that the higher gaze angle results in a
greater percentage of blinks that are incomplete.
It has been suggested that incomplete blinks are
not effective because the tear layer being replenished
is defective and not a full tear layer.
Office air environment is often low in humidity
and can contain contaminants. This has been noted
as the cause of Sick Building Syndrome.
Additionally, the static electricity generated
by the display screen itself attracts dust particles
into the immediate area. These can also contribute
to particulate matter entering the eyes, leading
to dry eye symptoms.