SPORTS VISION
Contact
Lenses for Sports: A New Ball Game
Athletes
have higher visual demands, and custom lens designs can help meet them.
By David G. Kirschen, OD, PhD, & Daniel
M. Laby, MD
"Keep
your eye on the ball." How many times have we said that to our sons and daughters
as they stood at the plate awaiting a pitch or at the baseline waiting to return
serve? As is the case with most quotations, a grain of truth sparkles in that sentence.
How the Pros See
First, we'll give you some background. In 1992
we initiated a study of the visual function of professional athletes. Our work began
with the Los Angeles Dodgers and has since spread to teams on both coasts (New York
Mets and Boston Red Sox) as well as to other sports such as hockey (Los Angeles
Kings). In an article published several years later, we detailed our findings regarding
the visual skills of these elite, professional athletes.
It
wasn't surprising that the players had visual abilities better than the average
population, but what was surprising was exactly how much better. In fact, the first
year we tested players, we used a standard vision testing system available at the
time (the Mentor BVAT System). We set up and calibrated the system according to
the manufacturer's specifications and found that the vast majority of the players
we tested were able to correctly read the entire 20/15 line, the smallest line of
letters available on that system. The next year, when we arranged the visual acuity
tests, we calibrated the test for a 10-foot testing distance, but in fact placed
the test screen at 20 feet from the subject. This allowed the maximum visual acuity
testable by the system to increase from 20/15 to 20/7.5, a level beyond the resolution
ability of the human eye.
After several seasons of testing,
we reviewed our data and published our findings. Among the most intriguing was the
average visual acuity of professional baseball players. Although 20/20 vision is
considered normal for the general population, the baseball players had an average
visual acuity of 20/12.5. In fact, very few of the players had acuities less than
20/20.
We tested all players as they play;
most wore no correction, some wore contact lenses and a few wore spectacles. Partnered
with the visual acuity results were our findings related to contrast sensitivity.
In fact, visual acuity can be considered a subset of contrast sensitivity, tested
at the high spatial frequency end of the contrast sensitivity curve. On all tests
of contrast sensitivity, and at all spatial frequencies, the baseball players had
a greater sensitivity than did the general population. In addition to the above
tests, we also measured two different tests of distance stereo acuity as well as
contrast sensitivity under conditions of glare. As in the initial tests, the baseball
players scored significantly higher on these tests when compared to the general
population.
When dealing with a fast-moving, small
target, such as a baseball, tennis ball or hockey puck, the ability to clearly visualize
the target is critical to one's performance in the sport. Visual abilities such
as visual acuity and contrast sensitivity give the player the ability to see the
target earlier, react faster and complete the necessary task more successfully.
Therefore, detecting errors or anomalies in the visual system in this regard is
something that we as eyecare practitioners can use to help our player-patients perform
at a higher level in their chosen sport.
Measuring Visual Function
Before discussing methods to correct these visual
functions, we should review how practitioners are currently testing them. Fifteen
years ago, we didn't know what to expect as we began working with elite athletes.
Over the years we've used a wide range of off-the-shelf testing systems, none of
which provided the accuracy and detail needed to evaluate these exceptional patients.
Recently, we discovered that there simply wasn't an all-in-one eye testing system
that met the needs of a sports vision specialist. In partnering with M&S Technologies,
we were able to create a system built to the specifications needed for reliability,
accuracy and the ability to test to the level needed by professional athletes. This
system, designated the PSVTS (Professional Sports Vision Testing System) is capable
of meeting the needs of the sports vision specialist. The system runs on either
a laptop, for in-the-field testing, or on a standard M&S desktop for use in
the exam lane. This is the system we currently use when testing our professional
athletes.
The Role of Contact Lenses
Now, and during the past 15 years, contact lenses
are the preferred method of optical correction of refractive errors in professional
baseball players. The players appreciate the ease of contact lens use, as well as
contact lens comfort when compared to spectacle lenses. Although the brands vary,
we fit all players with daily wear lenses and ask them to not use the lenses on
an extended wear basis.
One of the "pearls" we've learned over the
years deals with the importance of low-power prescriptions. In the general population,
visual acuity of 20/20 — or even 20/25 — is often not corrected, and practitioners
rarely prescribe contact lenses. In the baseball world, visual acuity at this level
represents a significant decrease from the average of 20/12.5. Practitioners should
determine prescriptions that optimize the player's acuity. Refractions shouldn't
stop at an arbitrary vision level (like 20/20). You should continually refine the
refraction to achieve optimum vision. Because binocularity is key for elite on-field
performance, you should determine a careful balance that equalizes the accommodative
effort in the two eyes (von Graefe, Turville, Polaroid, etc). We trial frame all
our prescriptions to demonstrate to the player the improvement of acuity we can
achieve.
The Importance of Torics
In our experience, prescribing low-power contact
lenses can have a dramatic effect on a player's visual acuity as well as on his
on-field performance. Although we prescribe many spherical lenses, toric lenses
have become an important part of our refractive armamentarium. We can't overstate
the importance of correcting cylindrical refractive errors because it's most often
this type of refractive error that limits the player's visual acuity.
Because of the different fits of toric
contact lenses, we use lenses from several manufacturers in an effort to obtain
the most accurate on-axis fit possible. We've been impressed with the stability
of the Acuvue Advance for Astigmatism lenses by Vistakon. They offer players consistently
good vision and are stable with each blink and during eye movements.
Often, we pursue several different
trials until the fit is correct and the visual acuity is optimized. We're able to
successfully fit almost all players with the lenses that are currently available.
However, each year we've had a handful of athletes in whom we would have liked to
use either lower power cylinders (–0.25D or –0.50D) or lenses available
in oblique axes. These players were forced to either accept less-than-optimal visual
acuity or to use spectacle lenses. It would be wonderful if contact lens manufacturers
would expand their power and axis selections to provide lenses needed for this special
population.
One of the exciting possibilities available
just over the horizon is the ability to correct higher-order optical aberrations
with contact lenses. Although we're only beginning to learn about these subtle sources
of image distortion, it appears that they can be significant if present. Aberrations
such as coma, trefoil and others have a detrimental effect on standard visual acuity
as well as a more subtle effect on image clarity, which can affect the detection
of critical visual cues like finger placement and spin on a pitched ball.
As an outgrowth of laser refractive
surgery, portable aberrometers are becoming more widely available. At the same time,
manufacturers are developing processes in which the personal aberration data for
a specific eye is used to create a custom contact lens for that patient (See "Custom
Lens Design" sidebar on p. 32). In addition to correcting the higher-order aberrations,
you can custom design these lenses to correct lower-order aberrations as well. Practitioners
can specify and correct the precise astigmatic refractive power and axis, thus eliminating
the need to use standard lenses that may not fit precisely nor fully correct the
refractive error. This is an exciting advancement for athletes of all types, and
we look forward to fitting these lenses and evaluating their benefits.
Tinted Lenses in Sports
Earlier, we presented the differences between
the visual functions of the general population and of professional athletes. In
addition to visual acuity, excellent contrast sensitivity is an important component
of the visual system of these athletes. Although the field is new, the use of tinted
spectacle or contact lenses is beginning to gain recognition as a bona fide method
of contrast sensitivity correction and enhancement.
Sports enthusiasts have long recognized that
tinted lenses can improve their ability to view and detect objects. From skiers
who in flat lighting have used tinted goggles on the slopes to more easily see moguls,
to hunters who have used yellow-tinted lenses to improve their contrast sensitivity
and shooting ability, tints of different colors have had a role in sports.
Recently, Bausch & Lomb introduced
the Nike MaxSight contact lens series. Although independently published, peer-reviewed
data concerning the benefits of these lenses is lacking, they do seem to have a
place in sports vision correction. The MaxSight lenses come in amber and grey-green.
Each tint has a list of recommended sports, and they've been popular with players
since their release almost two years ago.
We've fit several baseball players
with these lenses and have found that although there is a high attrition rate (many
players initially wear them and eventually stop), a certain number of players find
them beneficial and continue to regularly wear them during day games.
Step to the Plate
Contact lenses in sports have evolved along with
the use of contact lenses in the general population. Until recently, eyecare practitioners
have applied the same standard and correction techniques to athletes that they use
on other patients. As we learn of the differences in the visual function and visual
requirements of professional athletes, we've adapted our refractive correction techniques
to not only correct players to the norms of the general population, but to move
them farther to the levels found among professional athletes. Coincident with this
has been an explosion in technology, allowing for not only correction, but for enhancement
of vision using new types of lenses.
The ability to custom fit a contact lens containing
higher-order optical correction, along with custom correction for lower-order aberrations
in amounts that were previously impossible, is exciting and significant. Coupled
with the ability to enhance contrast sensitivity with tinted contact lenses, we
find ourselves on the threshold of a new era in sports vision, one in which every
eyecare practitioner should be a part.
For references, please visit
www.clspectrum.com/references.asp
and click on document #133.
Dr. Kirschen is currently the Chief of Binocular
Vision and Orthoptic Services at the Jules Stein Eye Institute at the David Geffen
School of Medicine, UCLA. He has been in private practice in California for 35 years
while continuing his teaching and research efforts.
Dr.
Laby has served as staff ophthalmologist for several professional sports teams including
the LA Dodgers, NY Mets and LA Kings among others. He is an assistant professor
of Ophthalmology at Harvard Medical School.
Contact Lens Spectrum, Issue: December 2006