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EFFECT OF WEARING
SINGLE-VISION &
PROGRESSIVE LENSES
ON
EYE &HEAD MOVEMENTS
DURING THE
GOLF PUTTING STROKE
n
George K. Hung, Ph.D.
a
n
Kenneth J. Ciuffreda O.D.,
Ph.D.
b
n Arkady Selenow O.D.
c
n George A. Zikos O.D., M.S.
c
a. Dept. of Biomedical Engineering, Rutgers
University, Piscataway, NJ
b. Dept. of Vision Sciences, State University of
New York, State College of Optometry, New
York, NY
c. Manhattan Vision Associates/Institute of Vi-
sion Research, New York, NY
Abstract
This study investigated the effects of differ
-
ent progressive lenses and a single-vision
lens on eye, head, and putter motions dur
-
ing the golf putting stroke in presbyopes.
Six subjects ranging in age from 49 to 69
years, with golf experience ranging from
modest to high, participated in the study.
Three lens conditions were tested: sin
-
gle-vision distance lenses (SV), newer
“soft” design (PAL1), and older “hard” de
-
sign (PAL2) progressive lenses. The two
progressive lenses have different interme
-
diate zone widths. For each condition, the
subject completed 15 putts to a standard
size golf-hole target 9 feet away. Eye, head,
and putter movements were recorded. The
data were analyzed over the interval from
the beginning of the putting stroke to the
moment of ball impact. The root mean
square (RMS) of the eye, head, and putter
movements within this time interval were
calculated for each record, and the data
were averaged across subjects. Putting ac
-
curacy was also monitored. The results
showed that the mean RMS values of the eye
movements were not significantly different
among the three conditions, although it was
slightly smaller for the PAL2 condition.
The mean head movement RMS values were
not significantly different between the SV
and PAL1 conditions, whereas it was sig-
nificantly higher for the PAL2 than the
PAL1 condition. In addition, putt ampli-
tude, duration, and accuracy were not sig-
nificantly different among the three
conditions. There were no obvious differ
-
ences between experienced and inexperi
-
enced golfers. For the PAL2 condition, the
larger head movements observed (and the
corresponding smaller eye movement vari
-
ation) may be due to its smaller intermedi
-
ate zone width. Progressive addition lens
users have been previously observed to re
-
main well within the boundaries of the in
-
termediate zone of clarity, possibly by
adopting a conservative eye movement
strategy, and therefore are forced to com
-
pensate with larger head movements. The
results provide new and useful guidelines
for the future design of progressive lenses
to improve their performance during out
-
door activities such as golf.
Key Words
eye movements, golf putting movements,
head movements, presbyopia, progressive
addition lenses, putting accuracy, single vi
-
sion lenses, wireless sensor system
INTRODUCTION
S
ports science and sports medi-
cine are becoming a popular
means of addressing specific
questions posed by athletes and their
trainers concerning the body’s forces and
actions during athletic motions. It has, for
example, provided valuable information
about the golf swing and physical forces
impacting on the golf ball.
1,2
Much of this
information has been obtained using
high-speed photography and video sys
-
tems spanning almost a century.
3-7
In
-
deed, the components of the golf swing
have been studied in great detail over the
past 50 years. However, there is a surpris
-
ing lack of objective simultaneous mea
-
surements of eye and head motion during
the golf swing, especially for putting.
8
Putting is a crucial element in golf.
9-11
This is demonstrated by statistics com
-
piled by the Professional Golfers Associa
-
tion, which showed that the best players in
the world expend approximately 40% of
their total strokes in a round on putting.
12
Professional golf instructors and sports
psychologists have stressed the impor
-
tance of minimal or no eye and head
movements throughout the putting stroke.
The eyes are important because they pro
-
vide accurate perception of the distance
and direction to the target hole location to
result in successful execution of a putting
stroke. If the eyes are fixated elsewhere at
a position other than the ball, this can lead
Journal of Behavioral Optometry Volume 17/2006/Number 5/Page 115
to an improper stroke and a missed putt.
Head position is also important because it
allows for maintenance of a stable visual
environment. Head movement during the
stroke can lead to misalignment and a
missed putt.
With the increased number of baby
boomers playing golf, progressive addi
-
tion lenses (PALs) have become an impor
-
tant component of golf activities. As one
ages, the accommodative response de
-
creases, and beyond the age of about 50
years, the crystalline lens acts essentially
as a fixed-focus optical system.
13,14
The
PAL can remedy this by providing a
means to see clearly as a continuum at far,
intermediate, and near distances. Thus,
during a round of golf, the PAL allows the
player to see the ball at address, midflight,
and at a far distance where the ball lands.
The need for clear vision through the PAL
is particularly important during putting,
since viewing through different portions
of the PAL can affect target clarity and
awareness of surround during the execu-
tion of the putting stroke.
Different PAL designs provide differ-
ent attributes. The older “hard” design
lenses have an abrupt and narrow inter-
mediate zone, which may induce more
head movements for accurate visualiza-
tion.
15-17
On the other hand, the newer
“soft” design lenses have a less abrupt and
wider intermediate zone that provide a
larger field of view, thus requiring less eye
and head movements for viewing a
scene.
15-17
These attributes may have dif
-
ferent effects on vision function during
physical activities such as golf. This study
investigated the differences in eye and
head movements of golfers during the
putting stroke while wearing single-vision
(SV), newer “soft” design (PAL1), and
older “hard” design (PAL2) progressive
lenses.
METHOD
Apparatus
A wireless sensor system was custom-
designed by the first author. It allowed for
simultaneous recording of eye, head, and
putter motions during the golf putting
stroke (Figures 1 and 2). Head movements
were measured using an accelerometer
placed in a small circuit board, which was
mounted on the beak of a visor.
18-20
The
eye sensor consisted of infrared emit
-
ter-detector pairs that were aimed at the
horizontal limbal boundaries of the eye,
where the reflectance is directly related to
horizontal eye position. A flexible wire
and adjustable plastic assembly were an
-
chored on the side of the visor to position
the eye sensor at a fixed distance in front
of the left eye. This assembly configura
-
tion provided for full adjustment of sensor
position in different users. In addition,
putter motion was measured using an ac-
celerometer placed in a circuit board
which was mounted on the shaft of the
putter. The two circuit boards on the visor
and the putter shaft contain antennas that
send the head, eye, and putter signals to a
receiving board, which is plugged directly
into the USB port of the PC for serial data
transmission.
Subjects and Procedure
Four male and two female subjects,
ranging in age from 49 to 69 years, partici
-
pated in the study. Two of the male sub
-
jects were experienced in playing golf,
whereas the others were novices.
Three lens conditions were used:
1. Single vision CR-39 lens spectacles
prescribed according to the subject’s
distant vision correction.
2. PAL 1, which is a “soft” newer design
with a 3.9mm(wide) intermediate
zone.
3. PAL 2, which is a “harder” older de
-
sign with a 2.3mm intermediate zone.
Both PAL designs incorporated the sub
-
ject’s present prescription. The wider in
-
termediate zone (PAL1) lens has less
unwanted astigmatism in the periphery,
while the narrower intermediate zone
(PAL2) lens has more unwanted astigma
-
tism in the periphery. None of the subjects
were adapted to any one of the lens styles,
nor were they given any specific instruc
-
tion on how to use the lenses.
The sequence of spectacle lenses
tested was randomized among the sub
-
jects. For each condition, the subject com
-
pleted 15 putts to a standard size golf-hole
target 9 feet away on a smooth artificial
grass environment. Eye, head, and putter
movements were recorded over 3-sec in
-
tervals at a 64 Hz sampling rate using the
wireless sensor system (see Figure 3).
Data Analysis
The data were analyzed using pro
-
grams written in C++
a
and MATLAB
b
codes. The results were displayed in three
channels as position time courses for put
-
ter, eye, and head movements. Also dis
-
played were the corresponding velocity
traces. For each record, the beginning of
the putt (i.e., the take-away), as well as the
Volume 17/2006/Number 5/Page 116 Journal of Behavioral Optometry
Figure 1. Visor with head sensor (attached to
beak of visor) and eye sensor (below the visor).
Figure 2. Subject wearing spectacle lenses and
visor with attached head and eye sensors.
Figure 3. Subject putting while wearing recording
system containing eye, head, and putting motion
sensors.
end of the putt (i.e., return to the point of
impact), were marked visually on the PC
screen. The program calculated the RMS
of eye and head movements, as well as the
duration and amplitude of the putt, over
the marked time interval.
The data from each subject were aver
-
aged, and the averaged data for the six
subjects were used in the statistical analy
-
sis. One-tailed t-tests (MATLAB
b
Statisti
-
cal Analysis Toolbox) were performed to
assess the statistical significance of differ
-
ences between the progressive and SV add
lenses for the various parameters: RMS of
eye and head movements, putt amplitude,
putt duration, and the percentage of putts
made.
RESULTS
Typical records during the putting
stroke are shown for small (Figure 4a) and
large (Figure 4b) amounts of eye and head
movements before ball impact. The data
were converted to equivalent linear dis
-
placement (in cm) on the putting surface.
The mean RMS values of the eye
movements were not significantly differ
-
ent among the three conditions, although
it was slightly smaller for the PAL2 condi
-
tion. The mean head movement RMS val
-
ues were not significantly different
between the SV and PAL1 conditions,
whereas they were significantly higher for
the PAL2 versus the PAL1 condition
(t-test, p < 0.05). In addition, putt ampli
-
tude, duration, and percentage made were
not significantly different among the three
conditions (see Table 1). There were no
obvious differences between the experi
-
enced and inexperienced golfers.
DISCUSSION
Among many other factors, there are
two physical factors that may lead to
missed putts. Putting on a smooth artifi
-
cial surface does not necessarily mean a
perfectly flat surface. There may be grain
and slight contour variations even for an
Journal of Behavioral Optometry Volume 17/2006/Number 5/Page 117
Figure 4a. Record showing relatively small eye and head movements before ball impact at 1.5 sec
(vertical dashed lines) with PAL2 lens. Upwards on plot is towards the hole. Putter position is estimated
from acceleration data, and is used primarily to determine the point of impact.
Figure.4b. Record showing relatively large and variable eye and head movements before ball impact at
about 1.5 sec (vertical dashed lines) with PAL1 lens.
Table 1. Average Values (n=6)
SV PAL1 PAL2
Eye (rms, cm) 6.23 6.77 5.37
Head (rms, cm) 4.70 4.64* 5.95*
Putt amplitude
(cm)
34.5 36.3 36.2
Putt Duration
(sec)
0.86 0.90 0.90
Putt (% made) 54.0 39.6 42.8
* = p<0.05
apparently straight putt, similar to actual
greens that appear to be flat. Nevertheless,
the subjects were given a few trial putts
prior to the experiments, and this in part
allowed them to compensate for any
“break” (i.e., a specific golf term referring
to the expected turn of the ball due to the
contour or grain) on the artificial surface.
Also, the PAL lenses may contribute in
part to a misreading of the true position of
the target due to the prismatic effect
through the periphery of the lens. Thus, to
accurately assess alignment of the putt,
the subject should look at the golf hole
through the central portion of the PAL
lens by turning the head fully rather than
partially, as is normally done with single
vision lenses.
The amount of accommodation
needed for the putts was calculated to
range from 0.68 to 0.77 D, which corre
-
sponds to a range of distances from the eye
to the ball from 148 cm to 131 cm. If the
subject viewed through the central dis
-
tance-refraction portion of the PAL lens,
and accounting for a depth of focus of
about ±0.25 D,
21,22
this would leave about
0.5 D of accommodative stimulus. Thus,
there would be a small amount of blur ex-
cept for the younger presbyopes, who may
be able to accommodate for the remaining
dioptric stimulus. However, all of these
presbyopic subjects should be able to see
the ball clearly by a slight upward tilt of
the head to look through a particular por-
tion of the progressive add lens that just
compensates for the optical power of the
target. But this may not be the most com
-
fortable position, so subjects may com
-
promise by reducing the amount of head
tilt to achieve a reasonably comfortable
posture while permitting a small amount
of defocus blur.
The results of the present investigation
demonstrated clear but subtle differences
in eye and head movements during golf
putting with the three lenses. For the PAL2
lens, which has the most restricted clear
field-of-view, head movement variation
was significantly greater, while eye move
-
ment variation was smaller than with the
PAL1 lens. Regardless of the type of lens,
head and/or eye movements are undesir
-
able during golf putting, as golf-teaching
professionals stress in their lessons.
9
Pre
-
sumably, the presence of such movements
would impact adversely on putting accu
-
racy. While putting accuracy was not sig
-
nificantly different for the three lenses, it
was about 10% better with the SV versus
either PAL lens. Perhaps this finding was
not statistically significant due to the rela
-
tively small sample size. An expanded
study with a larger sample size may deter
-
mine whether it is indeed statistically sig
-
nificant, and is so, this percentage
difference could have important perfor
-
mance and thus lens design consequences.
The present findings are consistent
with earlier studies in our laboratory with
PAL lenses, but involving various near vi
-
sion reading tasks.
15-17
In those studies, as
the PAL intermediate zone became nar
-
rower and restricted the clear field-of-
view, both eye and head movement ampli
-
tudes increased, as well as the time to at
-
tain fixational stability after a saccade.
Other dynamic aspects of eye and head
movements, such as peak velocity, were
not affected and remained normal.
The present findings may also provide
important information with respect to fu
-
ture PAL design. The greater the clear
field-of-view, presumably the more accu-
rate and time-optimal is one’s sensori-
motor performance.
23
Although one op-
tion would be to wear SV lenses designed
to have a wide and clear field-of-view for
putting only at an intermediate distance, it
would be less cumbersome and problem-
atic to have a lens that was satisfactory at
all golf distances, which would include a
range from far (i.e., several hundred
yards) to intermediate (i.e., the eye to ball
distance during putting) distances. Fur
-
thermore, the same PAL could be used for
the relatively infrequent near tasks at 40
cm or so, such as reading the scorecard.
Thus, a multi-function PAL spectacle lens
designed specifically for golfing and re
-
lated tasks would be of great benefit to the
serious golfer who is striving to obtain op
-
timal conditions for maximum perfor
-
mance. If such a lens were available, it
could reduce or eliminate the presence of
undesirable astigmatism and distortion
outside this zone, which create defocus
and prismatic displacement effects. These
factors might affect the determination of
the “line” based on judgment of the cup’s
absolute distance and direction through
this peripheral region. Thus, the improved
PAL lens could reduce the visual/
proprioceptive mismatch that would oth
-
erwise be present, thus leading to im
-
proved perception of these critical target
location parameters.
CONCLUSION
This study quantified the effects of
single-vision and progressive lenses on
eye, head, and putter motions during the
golf putting stroke. The wireless device
provided a convenient means to measure
these different factors simultaneously
without subject-movement limitations. It
was found that subjects wearing the pro
-
gressive addition lens with the narrower
intermediate zone (PAL2) exhibited
slightly smaller eye movements than with
the lens having a wider intermediate zone
(PAL1). On the other hand, in apparent
compensation for the restricted clear
field-of-view, subjects wearing PAL2 ex
-
hibited greater head movements than
PAL1. These findings have important
ramifications in the design of PAL lenses
for sports and in the workplace.
Dr. Hung has financial interest in the
wireless sensor system used in this study.
ACKNOWLEGMENT
We thank Abhijit Tamba and Wayne
Spencer for assistance with the experi-
ments.
Sources
a. http://www.codeproject.com/
b. The MathWorks
Natick, MA
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Corresponding author:
George K. Hung, Ph.D.
Dept. of Biomedical Engineering
Rutgers University
617 Bowser Road
Piscataway, NJ 08854
shoane@rci.rutgers.edu
Date accepted for publication:
August 9, 2006
Journal of Behavioral Optometry Volume 17/2006/Number 5/Page 119
EDITORIAL CONTINUED
almost 4%. This can be interpreted as
evidence that binocular difficulties
are given somewhat more attention
in the practice of primary care op
-
tometry than some have alleged.
The study lists the top 40 most
frequent diagnoses that were re
-
ported. Not surprisingly, the basic re
-
fractive conditions and presbyopia
accounted for almost 51% of the di
-
agnoses. However, taken together,
Accommodative Dysfunction, Re
-
fractive Amblyopia, Esotropia and
Convergence Insufficiency accounted
for 2.04% of the diagnoses. This is
close to the 2.45% for the combina
-
tion of Glaucoma Suspect and Open
Angle Glaucoma.
It must be pointed out that the
place of binocular vision disorders in
the entire profession is not repre
-
sented by the study; those in “special
-
ized practice” did not meet the
criteria for primary care optometric
practitioners. Nevertheless, I interpret
the report as indicating that, at least
in terms of diagnostics, binocular vi-
sion disorders remain an integral part
of primary care optometry. It is cer-
tainly not dead; rather, it is alive, but
not kicking. The study should pro-
vide valuable information for the
strategic planning of all organizations
involved with the education of op
-
tometrists, and particularly for the
Optometric Extension Program and
the College of Optometrists in Vision
Development.
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