Eye Fatigue and Glare
Glare is the single most common complaint from readers.
They want to know what causes it and why such sensitivity
to sunlight (photophobia) impacts them. Then, they want
to know what can be done to minimize or resolve this
stressful phenomenon. Note: Glare is not confined to
bright sunlight in the heat of summer. Snow glare and
computer glare also rank high in causing vision problems.
According to the National Institute for Ocupational Safelty
and Health (NIOSH), glare constitutes 50% of users'
complaints. Symptoms given by people using video display
terminals are: burning eyes, irritated eyes, and blurred
vision. Many persons with RP (who seem to suffer more
from glare) use light tinted sunshields for indoor tasks
including computer work.
The following information on tinted sunshields is derived
from Sunglasses", an article by Jeanette Berry, M.A., and
Jeffrey Barnett, and which was kindly submitted by Linda
Cline, customer representative for NoIR Medical
Technologies. It is condensed here for the sake of brevity.
"Eye fatigue is a common problem noted by visually challenged persons. Though it has been associated with
infrared radiation, it is more commonly a glare response.
Glare is the sensation produced by the reflection of, or
over-abundance of visible light within the field of vision.
Glare can cause discomfort or a reduction in visual
performance. Glare can impact vision by veiling, dazzling
or temporarily blinding.
"When the eye is exposed to sunlight, the natural response
is for the pupil to contract its opening and the eyelids
squint,
thus decreasing the amount of light that enters the eye. If
glare is present, the eye strains to see objects through the
glare. All of this involves a physical reaction of the eye and
its surrounding muscles. Over a period of time, eye fatigue
induced by this response, also becomes a problem, thus
furthering to diminish visual functioning at that time.
"The appropriate selection of sunwear can effectively
address the problems caused by the sun's damaging rays
and glare- related eye fatigue. ...While all sunglasses filter
varying amounts of visible light, many do not protect
against the damaging rays that are also present.
Paradoxically, dark lenses may allow more UV rays to
reach the eye than no lenses at all. By reducing the visible
light (shading the eye,) the pupil may enlarge rather than
allowing the natural aversion reflexes to constrict it. This
then allows a greater quantity of all rays into the eye. The
net effect--more damaging rays enter the eye.
Unfortunately, the only way to know if a sunglass has
protective qualities is to carefully read the promotional
literature provided by the
manufacturer.
"The important factors involved in accurately selecting
sun- wear can be broken down into categories: 1) protection
needs; 2) lens type; and 3) lens color and transmission.
"Protection needs would take into consideration any
ocular pathology present, the need to protect from UV, or
blue light, and the location that the protection needs to be
placed (in front or to the side of the eye, etc.,) based on
the task needing to be accomplished.
"There are many types of lens materials that can be used
in the manufacturing of sunglasses. Some, such as glass,
CR-39, and polycarbonate, have inherent protective
qualities which, by the use of coating or absorbing
additives, can enhance these capabilities. The most
common of these is UV protection. It is possible to find
some manufacturers who do add IR protection as well,
though it is much less common.
"Several types of lenses are available in both prescription
and non-prescription sunwear:
"The constant density lens has its color and transmission
fixed and is even across the lens. It is best if tinted during
the original manufacturing or in the finishing stages of
frame assembly. This allows the edges to have the same
color as the rest of the lens.
"The photochromatic lens is sensitive to UV rays and is
able to adapt to light and dark environments as necessary.
"The mirror lens adds and extra buffer which reflects
unneeded light.
"The polarized lens reduces reflected surface glare (such
as that of light off of water) by only allowing light to pass
through which strikes the lens at a certain prescribed
angle.
"Certain ocular pathologies may demand higher or lower
transmissions levels. Visual functioning reacts to color, so
the correct selection of lens color can enhance residual
vision, while a color that is not optimal can significantly
decrease visual functioning.
"There is no short and easy answer to appropriate
sunwear
selection. The determination is ultimately made on the
subjective level and is almost unavoidably a trial and error
process at the onset. Being an educated consumer is the
best way to start. In essence, the key to choosing the
correct sun- wear is exploration. Be ready to try new
colors or frame features. When narrowing down the
possibilities, it may be helpful to remember this equation
and its meaning:
PHYSIOLOGY + TASK + ENVIRONMENT = LENS
"Physiology: What type of problems are present at this
point in time. What protection is needed.
"Task: What needs to be accomplished while wearing the
sunglasses (small detail or general picture.)
"Environment: Type of lighting available (clear, sunny,
haze, rain. etc.,) is the lighting direct or indirect (shade
trees, high noon, etc.)
"By taking into account these three variables and through
careful examination of the available types of lenses,
selection of sunwear which not only looks good but works
well can be made."
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©1997,2000 Texas Assn of Retinitis Pigmentosa Inc
This page last updated 12/11/97 8:32:50 PM
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