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International Journal
of Ophthalmology
2017; 10(9): 1460-1464
·Investigation·
Visual efficiency among teenaged athletes and
non-athletes
Rokiah Omar1, Yau Meng Kuan1,
Nurul Atikah Zuhairi1, Faudziah Abd Manan2, Victor Feizal
Knight3
1Optometry & Vision Science Program,
School of Healthcare Sciences, Faculty of Health Sciences, University
Kebangsaan Malaysia, Jalan Raja Muda Abdul Aziz, Kuala Lumpur 50300, Malaysia
2Department of Optometry & Vision
Science, Kulliyyah of Allied Health Sciences, International Islamic University
Malaysia, Bandar Indera Mahkota, Kuantan 25200, Pahang, Malaysia
3Faculty of Medicine and Defence Health,
National Defence University of Malaysia, Sungai Besi Camp, Kuala Lumpur 57000,
Malaysia
Correspondence to: Rokiah Omar. Optometry
& Vision Science Program, School of Healthcare Sciences, Faculty of
Health Sciences, University Kebangsaan Malaysia, Jalan Raja Muda Abdul
Aziz, Kuala Lumpur 50300, Malaysia. r_omar@ukm.edu.my
Received: 2017-02-22
Accepted: 2017-03-31
Abstract
AIM: To
compare visual efficiency, specifically accom-modation, vergence, and
oculomotor functions among athletes and non-athletes.
METHODS: A
cross-sectional study on sports vision screening was used to evaluate the
visual skills of 214 elementary students (107 athletes, 107 non-athletes), aged
between 13 and 16y. The visual screening assessed visual parameters such as
ocular motor alignment, accommodation, and vergence functions.
RESULTS: Mean
visual parameters were compared between age-group matched athletes (mean age
14.82±0.98y) and non-athletes (mean age 15.00±1.04y). The refractive errors of
all participants were corrected to maximal attainable best corrected visual
acuity of logMAR 0.0. Accommodation function assessment evaluated amplitude of
accommodation and accommodation facility. Vergence functions measured the near
point of convergence, vergence facility, and distance fusional vergence at
break and recovery point. Ocular motor alignment was not statistically
significant between both groups. Athletes had a statistically significant
amplitude of accommodation for both the right eye (t=2.30, P=0.02)
and the left eye (t=1.99, P=0.05). Conversely, non-athletes had
better accommodation facility (t=-2.54, P=0.01) and near point of
convergence (t=4.39, P<0.001) when compared to athletes.
Vergence facility was found to be better among athletes (t=2.47, P=0.01).
Nevertheless, non-athletes were significantly better for both distance negative
and positive fusional vergence.
CONCLUSION:
Although the findings are still inconclusive as to whether athletes had
superior visual skills as compared to non-athletes, it remains important to
identify and elucidate the key visual skills needed by athletes in order for
them to achieve higher performance in their sports.
KEYWORDS: accommodation;
phoria; vergence; athletes; non-athletes; sports
Citation: Omar R, Kuan YM,
Zuhairi NA, Manan FA, Knight VF. Visual efficiency among teenaged athletes and
non-athletes. Int J Ophthalmol 2017;10(9):1460-1464
INTRODUCTION
Vision provides key sensory information that is required for athletes to
perform in sports effectively. A high level of visual performance with good
visual processing is vital in most competitive sports[1]. Over the years, many studies
have postulated the possibility of athletes possessing significantly better
visual skills as compared to non-athletes, thus leading to their superior
on-field performance[2-5]. The basis of
better visual skills includes ensuring optimal refractive error correction to
achieve best visual acuity (VA) which is highly associated with visual
efficiency. It is also known that both accommodation and vergence have a close
relationship with and influence the binocular vision system[6]. Visual efficiency thus
encompasses the basic visual physiological processes comprising of accommodation
and vergence functions as well as ocular motility[7].
Visual skills have been found to be highly developed in athletes and
similar patterns have been observed in athletes engaging in both competitive
and non-competitive sports[8].
Nevertheless, the important link of visual skills to athletic performance is
often not described completely or neglected. Researchers have found certain
visual skills such as VA[9],
accommodation facility[10],
near point of convergence[2,10], vergence
facility[2]
and visual reaction time[4-5] to be significantly
better in athletes. Stine et al[11] also suggested that athletes with low phoria had
better binocular vision and depth perception.
Nonetheless, contradictions over visual skill findings between athletes
and non-athletes have been demonstrated in studies comparing the amplitude of
accommodation and ocular motor alignment between athletes and non-athletes,
where it was found that there were no significant differences between these two
groups[2,10,12]. Some researchers did note
differences between elite and novice players of particular sports, however,
this only attributed to less than 5% of the population variance in that
particular sports[12].
Athletes or coaches may not be aware that inadequacies in visual skills
could be a barrier to or have an impact on peak sports performance, whence
small improvements in visual skills may be critical enough to influence the
sports outcome[13].
Hence, this study aimed to compare the visual efficiency of athletes and
non-athletes.
SUBJECTS AND METHODS
Ethical Clearance Informed parental consent was obtained prior to the study’s
commencement. All consent was administered individually and the consent form
was signed by the parents before the students were enrolled into the study.
This study was approved by the National University of Malaysia Human Subject
Ethics Committee (UKM 1.5.3.5/244/NN-081-2013) as well as by the Ministry of
Education Malaysia [KP(BPPDP)603/5/JLD.10] and followed the tenets of the
Declaration of Helsinki.
Participants This research was a cross-sectional study with its sample size
determined using G*Power 3.0.10[14], with a power of 95% and an alpha level of 0.05 in a
two-sided test construct. A total of 214 elementary students (107 athletes, 107
non-athletes) aged between 13 to 16 years of old, regardless of gender
participated in this study. The mean age for the athletes was 14.82±0.98y while
for non-athletes was 15.00±1.04y, with almost equal numbers of male and female
participants enrolled. All participants were assessed using standard sports
vision screening, conducted at Bukit Jalil Sports School, Bukit Jalil,
Malaysian for athletes and Padang Tembak National Secondary School, Kuala
Lumpur, Malaysia for non-athletes. Prospective subjects with a history of
vision training, eye injury or ocular disease were excluded from this study.
Visual Parameters The battery of tests used in sports vision screening for this study
included refraction, best corrected distance visual acuity, distance ocular
motor alignment, accommodation and vergence functions. The accommodation
functions assessed were amplitude of accommodation and accommodation facility.
Vergence functions included near point of convergence, vergence facility, and
fusional vergence which included both positive and negative fusional vergence.
Refraction Participants’ refractive errors were determined using the retinoscopy
technique without pupil dilation by qualified optometrists. Best corrected
refractive errors were further refined through subjective refraction using the
crossed-cylinder technique. The refractive errors were measured in diopters
spheres (DS).
Best corrected visual acuity
Once participants had completed
refraction, the best corrected visual acuity was tested using an externally
illuminated ETDRS logMAR chart at a distance of 4 m. Each letter in the chart
scored 0.02 logMAR. Participants were encouraged to read the smallest
identifiable letter. Three logMAR charts with differently arranged letters were
used and presented to the participants in a randomized order to minimize the
effect of learning and chart memorization.
Accommodation Functions
Amplitude of accommodation Amplitude of accommodation was tested
using the best-corrected vision of each eye with an RAF rule. The target chosen
for the test on the RAF rule was 6/9 and it was moved slowly towards the
participant until they first reported a sustained blur. The test was then
repeated two more times for each eye. The average reading for each eye was
recorded in diopters (D).
Accommodation facility The dynamics and stamina of accommodative response were evaluated using
an accommodation facility test. This test was conducted using a Word Rock card
of text size 20/30 with a ±2.00 D lens flipper at a distance of 40 cm
monocularly, and then binocularly for one minute. Participants were asked to
clear out the letters as soon as possible once the lens flipper was placed in
front of their eyes. The results for this test was based on the number of
complete “flips” the participants were able to clear within one minute.
Accommodation facility was measured in cycles per minute (cpm).
Vergence Functions
Ocular motor alignment This study measured distance ocular
alignment using a Howell card with a 6 prism diopters (PD) base-down lens. The
test was conducted at a distance of 3 m from the spectacle plane, leveled to
the visual axis with the best refractive correction. A prism was placed in
front of the left eye to create a doubling effect to the viewed Howell card.
The magnitude of ocular misalignment was measured based on the participant’s
response to the arrow indicator of the number on the Howell card. An odd number
denoted exophoria while an even number signified esophoria.
Near point of convergence Participants were asked to fixate on a single target and report to the
examiner when the single target appeared as double when the target moved closer
to their eyes. Any ocular deviation or misalignment noted during the
measurement process signifies the near point of convergence objectively. The
near point of convergence was measured three times and the average reading
recorded in centimeters.
Vergence facility Vergence facility was tested at a distance of 40 cm using 12 base-out/3
base-in flippers placed on the left eye while fixating at a 0.18 logMAR target[15-16]. Participants were instructed to
make the letters single and clear as quickly as possible. The duration of test
was one minute. The number of “flips” were calculated in one minute and
recorded as cpm by the examiner.
Fusional vergence Fusional vergence measures the amount of
fusional strength reserve available to maintain fusion of a single target.
Distance negative fusional vergence (NFV) was measured prior to distance
positive fusional vergence (PFV) to avoid vergence adaptation. A base-in (BI)
and a base-out (BO) prism was used for NFV and PFV measurement respectively.
PFV and NFV break and recovery points were measured at 6 m with a horizontal
prism bar using a vertical row of 0.02 logMAR letter targets. The break and
recovery points were recorded in PD.
Statistical Analysis All data were analyzed using the IBM Statistical Package for Social
Sciences (v22.0, SPSS Inc., Chicago, IL, USA). Descriptive data for all visual
parameters were analyzed to show mean, standard deviation (SD), and range. The
Kolmogorov-Smirnov test was used to determine the status of data normality and
parametric tests were used when P>0.05. Independent t-test was
used to examine the visual parameters between athletes and non-athletes with
the level of significance at P<0.05.
RESULTS
All participants were required to undergo refractive assessment prior to
the measurement of other visual parameters. The mean refractive error for
athletes was found to be -0.85±1.47 DS while for non-athletes it was -0.87±1.72
DS with their binocular best corrected visual acuity being 0.01±0.03 logMAR and
0.00±0.01 logMAR respectively. The range of refractive errors for athletes was
from -6.00 to +1.00 DS while for non-athletes it was from -8.00 to +1.00 DS.
Analysis of the Kolmogorov-Smirnov test showed P>0.05, hence
parametric tests were used to analyze the findings.
Accommodation Functions Table 1 shows the descriptive data of the accommodation parameters of
athletes and non-athletes. Analyses showed that the athlete’s amplitude of
accommodation was significantly better than non-athletes for right, left and
both eyes respectively (t=2.30, P=0.02; t=1.99, P=0.05;
t=2.21, P=0.03). However, the accommodation facility was not
statistically significant between the athletes and non-athletes where the
analysis revealed (right eye, t= -0.87, P=0.38; left eye, t=-0.99,
P=0.32 and for both eyes, t= -2.54, P=0.01).
Table 1 Accommodation and vergence functions among teenaged athlete and
non-athlete groups
|
Category |
Mean±SD |
|||
|
Athlete (n=107) |
Non-athlete (n=107) |
|||
|
Accommodation functions |
Amplitude of accommodation (D) |
Right eye |
12.47±1.76a |
11.89±1.94 |
|
Left eye |
12.51±1.89a |
12.01±1.81 |
||
|
Both eyes |
12.49±1.76a |
11.95±1.83 |
||
|
Accommodation facility (cpm) |
Right eye |
12.14±4.55 |
12.73±5.30 |
|
|
Left eye |
12.59±4.68 |
13.30±5.70 |
||
|
Both eyes |
12.02±4.61 |
13.65±4.81c |
||
|
Vergence functions |
Ocular motor alignment (PD) |
0.13±1.37 |
-0.05±1.95 |
|
|
Near point of convergence (cm) |
5.93±3.60 |
3.81±3.44c |
||
|
Vergence facility (cpm) |
13.61±2.67c |
12.36±4.47 |
||
|
Distance negative fusional vergence (PD) |
Break |
7.33±3.68 |
11.18±4.46c |
|
|
Recovery |
4.59±2.89 |
6.38±3.28c |
||
|
Distance positive fusional vergence (PD) |
Break |
14.23±6.61 |
16.66±8.95c |
|
|
Recovery |
11.1±5.50 |
10.49±6.37 |
||
aP<0.05 and cP<0.001 denote significant difference
between athletes and non-athletes.
Vergence Functions Table 1 describes the mean and standard deviation for vergence
functions. Visual parameters on ocular motor alignment did not show any
significance between athletes and non-athletes (t=0.77, P=0.44).
Analyses showed that near point convergence was better in non-athletes compared
to athletes (t=4.39, P<0.001). Vergence facility was
statistically significant for athletes as compared to non-athletes (t=2.47,
P=0.01). Nevertheless, it was statistically significant for both distance
negative fusional vergence at break point (t=-6.89, P=0.001) and
recovery point, (t=-4.25, P=0.001). Analyses were statistically
significant (t=-2.26, P=0.03) for distance positive fusional
vergence at break point, but not at recovery point (t=0.77, P=0.44).
DISCUSSION
The majority of participants in this study were myopes with mild to
minimal astigmatism of 0.25 to 0.75 cylindrical diopter (DC). There were
similar refractive errors and best corrected visual acuity between both the
groups; probably because the research participants were entirely of an Asian
population[17].
However, the best corrected VA for athletes was below normal as the standard
recommended visual acuity for competitive athletes should be at least -0.1
logMAR monocularly and binocularly[18]. From our study, 63% of athletes had refractive
errors at distance but were not wearing any form of optical correction for
sharper and precise vision. Refractive error as low as 0.25 DS myope should be
corrected as studies have found that even low refractive errors may possibly
have a significant impact on sports performance[19] as athletes are required to
differentiate fine details clearly in sports play prior to choosing the
appropriate response. Stereopsis was also assessed between athletes and
non-athletes but found to be insignificant (P=0.57), as most of the
participants in this study consisted of junior athletes. Our results differ
from previous studies[2,8-9] as most compared stereopsis
between elite athletes and non-athletes.
Our findings were consistent with other studies with regards amplitude
of accommodation for monocular and binocular conditions, showing superiority in
athletes as compared to non-athletes and were within the normative values
described by Hofstetter[20].
Stronger accommodation was postulated to be linked to an athlete’s daily
on-field training; where the training would emphasize on attaining and focusing
on targets to achieve higher accuracy in sports play. Accommodation facility is
crucial for athletes to facilitate them in adjusting their focus rapidly for
stable and clear vision, especially when attempting to fixate from distance to
near or vice versa. Although athletes were found to have a higher amplitude of
accommodation than non-athletes, their accommodation facility was lower and
these findings were consistent with the study by Christenson and Winkelstein[2]. In this study,
accommodation facility was tested using ±2.00 DS lens flippers, in contrast to
other studies which used ±1.50 DS or ±1.00 DS lens flippers. Subsequent studies
have suggested using ±2.00 DS lens flippers for testing accommodation facility
as it enables better differentiation of participants from symptomatic and
non-symptomatic populations[16].
Due to the differences in the power of accommodation flippers used, the amount
of relaxation and stimulation of accommodation system would be dissimilar.
Higher power lenses would provide a lower range of relaxation and stimulation
of the accommodation system[21].
Ocular motor alignment was found to be highly related to the spatial
localization of an object in space, which is vital for sports performance in a
dynamic environment such as in badminton, tennis, football and hockey[19]. This study
noted that the athletic population studied were esophoric while the
non-athletes were exophoric. Previous literatures have shown that athletes with
esophoric eye posture tend to undershoot by seeing the object nearer to them
than it actually is while exophoric eye posture tends to be vice versa[19], which could
have a significant effect on athletes in dynamic sports requiring catching
and/or hitting a ball. Another factor to take into consideration is the conduct
of ocular motor alignment assessments in an uncorrected visual state. Though
the amount of ocular motor alignment found in both populations was almost
negligible and within the normative values as described by previous studies[7,22], this does not reflect the
true scenario of ocular motor alignment in athletes as most participants were
not wearing any refractive correction despite having refractive error.
There are contrasting views as to whether vergence functions should be
better in athletes as compared to non-athletes[2,12,23].
However, in this study, it was found that athletes were better in near point of
convergence than non-athletes, possibly because this test does not directly
relate to the visual task requirements needed in many sports. There are not
many studies conducted that include fusional vergence examination on athletes[12,24], hence direct comparison of
these studies was not possible. Non-athletes had a higher fusional range as
compared to athletes, indicating that athletes had lower compensation of their
visual binocularity system. However, athletes did have a better ability to
regain single vision after diplopia based on the analysis for distance PFV at
recovery. Previous studies have speculated the possibility of athletes having
narrower vergence ranges, which leads to a more precise spatial judgment
ability[19,24]. More studies
would be necessary to understand the relationship of vergence ranges in
relation to better spatial judgement and sports performance. Nevertheless,
vergence facility was reported to be superior in the athletes compared to the
non-athletes in this study supporting the idea that athletes can adjust their
vergence posture rapidly and accurately.
In contrast to previous literature, our study found non-athletes to have
better accommodation facility, near point convergence, vergence facility,
distance negative fusional vergence at break and recovery as well as distance
positive fusional vergence at break parameters, indicating better accommodation
and reserves than athletes. A direct comparison of data with the literature was
not possible because most of these studies were conducted using different
ethnic backgrounds, age groups, and sports background parameters.
In conclusion, only certain aspects of visual skills related to
accommodation and vergence were noted superior in athletes compared to
non-athletes while the other visual skills did not show that athletes were
better than non-athletes. Although inconclusive, this study provides a baseline
on the visual skills that need to be assessed and optimized in athletes to
maximize their on-field visual potential through the use of an effective visual
training program. All athletes should be advised to undergo regular eye
examination annually with a visual performance evaluation to ensure that visual
function would not be a limiting factor to their sports performance. Sports
vision examination would enable an athlete to have better insight on their
current level of visual efficiency which they can then use to compare with the
standards which may have been determined for athletes in certain sports.
Identification of these key visual skills have the potential to help athletes
excel in their sports.
ACKNOWLEDGEMENTS
The authors thank Farawahida Kasmira Fakaruddin, Esther Lau Siew Sieng,
teachers, as well as students from Bukit Jalil Sports School and Padang Tembak
National Secondary School for their assistance with data collection.
Foundation: Supported by
the Ministry of Higher Education Malaysia Sports Grant [No. KPT.N.660-7 Jld 7
(3)], UKM Research Code NN-2013-069.
Conflicts of Interest: Omar R, None; Kuan YM, None; Zuhairi NA, None; Manan FA, None;
Knight VF, None.
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