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Double Fault!
Ocular Hazards of a Tennis Sunglass
Michael F. Marmor, MD
Arch Ophthalmol. 2001;119:1064-1066.
Blue-tinted lenses are currently being marketed as devices to enhance
visual performance in tennis and as sunglasses for children. These include
the Bollé Competivision sunglasses (Bollé, a division of Bushnell,
Inc, Overland Park, Kan) and the ProSoft contact lens (Wesley Jesson, Des
Plaines, Ill), both of which are intended for tennis, and the Bollé
Kids Collection sunglasses. The Competivision lenses are the "official" lenses
of the US Professional Tennis Association (teaching professionals), and they
were given to linespersons at the 2000 French Open Championship (at Roland
Garros). Tennis players of all skill levels may be purchasing these tennis
lenses with the expectation of better performance—and of safety in the
bright sunlight. Kids may ask for "cool-looking" blue children's glasses.
However, I would argue that the spectral transmission characteristics of all
of these lenses make them not only ineffective with respect to visual performance
on most tennis courts (and elsewhere) but also a potential hazard to the eyes
in bright sunlight.
The color of these tennis lenses derives from a patent1
(PeakVision, Needham, Mass) that claims that the spectral characteristics
of the tint "provides an increase in perceived color contrast between . .
. an optic-yellow tennis ball or golf ball, and the background." The filter
is designed to pass light maximally at the wavelength of fluorescence from
a yellow tennis ball, with the idea that this will enhance its visibility.
However, Figure 1 shows that the
blue lenses block most of the yellow light that is normally reflected off
a ball (spectral yellow is near 580 nm but yellow is also perceived from a
mix of all wavelengths between green and red). These lenses pass primarily
blue and green light (tennis ball fluorescence peaks near 515 nm, which is
perceptually blue-green rather than yellow). The Competivision lens blocks
all UV light below 400 nm, and the ProSoft contact lens lets in about 10%
near 400 nm; both lenses pass 30% or more of violet light and block very little
of the blue light.
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Figure 1. Spectral curves for the colors
of tennis balls and for the transmission properties of Competivision, ProSoft,
and a neutral color lens (Bollé) (see text for manufacturer information).
The energy percentages are a transmittance for the lenses, and reflectance
and fluorescence for the tennis ball. The fluorescence peak near 515 nm overlaps
the transmittance peak of the blue lenses. Approximate wavelength ranges of
subjective color perception are shown, along with the beginnings of the ultraviolet
and infrared. Note that the blue lenses block most of the light coming from
the tennis ball. Tennis ball curves were redrawn from the blue lens patent,1 the ProSoft curve was redrawn from Wesley Jesson publicity
material, and the Competivision and Bollé neutral lenses were measured
on a laboratory spectrophotometer (model DU640; Beckman Coulter Inc, Fullerton,
Calif).
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From the standpoint of improving the contrast or visibility of a tennis
ball to enhance sports performance, this design is inherently flawed on any
court with a greenish surface, which comprises most hard and clay courts in
the United States. Through a blue-green lens, a yellow ball appears greenish
(Figure 2) and thus is less visible
against the green court (which will seem bright through this lens). The same
would apply for a yellow or white golf ball viewed against green grass. Furthermore,
blue light in general is less effective physiologically with respect to functions
such as acuity, contrast detection, and motion perception.2-3
In other words, critical perceptions are actually reduced rather than enhanced.
These bluish lenses will be of no visual benefit except possibly on a reddish
or amber court (such as the red clay of Roland Garros). Here, the ball may
appear to be relatively light against a darker court, but these lenses still
should not be worn because of the hazard associated with blue light.
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Figure 2. Photographs of tennis balls on
the Stanford University (Stanford, Calif) varsity tennis courts. A, With no
filter; B, through a Competivision lens.
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A statement4 on ocular UV radiation hazards
in sunlight, endorsed by the American Academy of Ophthalmology, the American
Optometric Association, and Prevent Blindness America, advises that sunglasses
should block 99% to 100% of the full UV spectrum (UV-A extends up to 380-400
nm). The document notes that additional protection for the retina can be provided
by lenses that reduce the transmission of violet-blue visible light. These
recommendations follow the findings of many researchers,5-9
and reflect concerns that both near-UV and visible blue light may contribute
to macular aging and degeneration. Blue lenses do exactly the opposite: they
block long wavelengths and admit the violet-blue end of the light spectrum.
They are not only substandard as sunglasses but could, under some circumstances,
be more hazardous than wearing no glasses at all. Because so much of the bright
(yellow) end of the light spectrum is blocked, the world appears subjectively
dark through blue glasses, and the wearer might spend extra time in the sun
or have a relatively dilated pupil. If either of these occurs, the eyes could
be exposed to more short wavelength light than without any lenses. Blue lenses
for children may have additional risks because of the higher transmission
of short wavelength light through the lens of a young eye.
My impression is that most of the visual problems from playing a sport
in bright sunlight are a result of glare and of the brightness of the sky,
which sets the general level of light sensitivity and can make a playing surface
appear relatively dark. This is why a tunnel appears black inside as we approach
it in sunlight. What can the ophthalmologist recommend? For tennis, wear a
cap and good sunglasses. Simply wearing a cap with a visor will not only reduce
glare but will also make the court appear relatively brighter (as does a tunnel
once we enter it). A neutral gray or amber sunglass that blocks 99% to 100%
of UV-A and UV-B light will provide additional protection and may even help
slightly to make the ball stand out (depending on the color of the court).
However, there is no rationale for a blue lens, whether for children, tennis
players, or anyone else. Ophthalmologists should be aware of the properties
and the risks of blue lenses to advise parents of young children and sports-minded
patients. Tennis players in particular should be aware that a blue lens commits
a double fault, and does not serve well for either perception or safety.
AUTHOR INFORMATION
Accepted for publication January 12, 2001.
Corresponding author and reprints: Michael F. Marmor, MD, Department
of Ophthalmology, Stanford University School of Medicine, 300 Pasteur Dr,
Room A-157, Stanford, CA 94305-5308 (e-mail: marmor{at}stanford.edu).
From the Department of Ophthalmology, Stanford University School of
Medicine, Stanford, Calif.
REFERENCES
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1. Moore JP, inventor, Kerns DV Jr, inventor. Apparatus for enhancing visual perception of selected objects in recreational
and sporting activities. US patent 5 592 245. January 7, 1997.
2. Mollen JD. Colour vision. Ann Rev Psychol. 1982;33:41-85.
FULL TEXT
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3. Mullen KT, Kingdom FAA. Colour contrast in form perception. In: Gouras P, ed. The Perception of Colour.
Boca Raton, La: CRC Press; 1991:198-217.
4. Ocular Ultraviolet Radiation Hazards in Sunlight. Schaumburg, Ill: Prevent Blindness America; 1994.
5. Mainster MA. Light and macular degeneration: a biophysical and clinical perspective. Eye. 1987;1:304-310.
6. Remé C, Reinboth J, Clausen M, Hafezi F. Light damage revisited: converging evidence, diverging views? Graefes Arch Clin Exp Ophthalmol. 1996;234:2-11.
FULL TEXT
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7. Winkler BS, Boulton ME, Gottsch JD, Sternberg P. Oxidative damage and age-related macular degeneration. Mol Vis. 1999;5:32.
PUBMED
8. Busch EM, Gorgels TG, van Norren D. Temporal sequence of changes in rat retina after UV-A and blue light
exposure. Vision Res. 1999;39:1233-1247.
FULL TEXT
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9. Sparrow JR, Nakanishi K, Parish CA. The lipofuscin fluorophore A2E mediates blue light–induced damage
to retinal pigmented epithelial cells. Invest Ophthalmol Vis Sci. 2000;41:1981-1989.
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