Twenty-nine expert table tennis players were chosen. These young male (18-25 years old) had at least five years experience and they were champion in different national and international games. The main inclusive criterion for champion invitation was their championship. According to table tennis ranking in Iran we call them on from top to down, and explained about the research. A specific time was fixed for every one. The elites were evaluated for any systemic and visual problems. They were asked about any history of medication and systemic disease. The following visual and ocular tests have been done for them.

1. Visual acuity test with Topcon chart projector at six meter and Snellen near acuity chart for forty centimetres. These tests have been done in photopic condition.
2. Objective refraction by static retinoscopy and autorefractometry and subjective refraction including: visual acuity, cross cylinder, Bichrome test has been done for every subject. Hyperopia lesser than 0.75, myopia, against the rule and oblique astigmatism lesser than 0.25 and with the rule astigmatism lesser than 0.5 considered normal and accepted in this study.
3. Ocular motility evaluations consist of heterophoria and fusional vergence recording at far and near distance. The results assessed according to compensation criteria.
4. Amplitude of accommodation measured by push up technique.
5. Biomicroscopy and ophthalmoscopy of the eye for all the subjects.

The entire tests for two groups were done in the clinic of the optometry in the Iran University of Medical Science (IUMS).

The table tennis champions compared with non-players. The control group age, education and sex were the same and similar visual and ocular exam were done for every subject. We try to match a champion with a specific non-player with same age, education and sex. According to an Iranian law "Every champion can enter the university (usually in sports college or university) without any qualifying entrance exam". Therefore most of champions are student and we could select the control group from other male students in IUMS. The systemic and medication history evaluated in same manner. Every person in the control group matched by an elite.

The main difference between table tennis player and control group was that, they don't play any ball- racket games seriously or even as a hobby.

After preliminary exams a code assign to every person in two groups. An optometrist that didn't know about subject's group measured the acuity in reduced luminance and facility of accommodation. He used +/-2.00 sphere lenses for accommodation facility. A near chart positioned at 40 centimetres in front of subject. He instructed to fixate at 20/25 row in well illuminated examine room (Griffin, 1988). The subject should read aloud every optotype that optometrist wants. At the same time the flipper power change. The subject asked about clearance of optotypes. The optometrist waits for clear vision in every change of flipper. He counts the cycles of flipper changes per a minute as a criterion for accommodation facility.

Acuity in reduced luminance is another test that the examiner did not know about the subject's group. A conventional visual acuity chart projector (Topcon, Japan) used for acuity measurement. An electrical current regulator changed the output light intensity of projector. Light intensity at acuity screen measured by a photometer (Leibold, Germany). Light intensity decreased to 10 cd·m-2 and visual acuity tested. For all the subject acuity measurement is done according to 75% correct answer for every row. All data was recorded in a specific record card that its code is unique for every person. The data analyzed statistically by Statgraphics statistical package.

Descriptive and analytic statistics have been you for recorded data. As it shown in table 1 the average and standard deviation of the conventional acuity measurements in two groups are the same. This result is predictable because one of the inclusive criterions for groups was 20/20 or better conventional acuity.

The equivalent sphere of the recorded refractive error shows that ametropia is lesser in table tennis players. However there is not a significant difference between two groups. The standard deviation is lesser in elite; it is mean that inter-subjects differences are lesser in this group. All of the results in preliminary exams aren't the same in two groups, but the differences are not significant. The results of preliminary exam in table tennis player are better than non-player. The average and SD of results are better in champions.

Two variables that evaluated in two groups are significantly different in table tennis player and non-players (Table 1). Facility of accommodation is significantly (p < 0.001) better in table tennis players. In facility test, as it shown in table 1, the frequency of clearance in sports man is 14 cpm but in other group it is 9 cpm. Visual acuity in reduced lumination is also significantly (p < 0.01) different in two groups. As it shown in table 1 acuity reduction in non-player is more prominent. In other word sports man can retain 20/20 acuity despite of luminance reduction. This is seen in a situation that all first acuity measurement was the same. Acuity changes and inter-subject differences in champion were lesser. It means that acuity is more stable in champions.

As the results shows there is significant differences between facility of accommodation and acuity in reduced lumination in champions and normal non-players. Development of these two parameters may improve the efficiency of visual system.

Facility development may shorten the time that visual system needs for taking a clear image. In table tennis fixation points change as fast as the ball and opponent velocity change. The velocity of ball is very high and the eyes should clearly see it. Therefore any person that can follow the ball as fast as possible, he would be more successful. Saccadic eye movements are used for fixation on the ball (Ripoll and Latiri, 1997). Suppression takes place in saccadic eye movements. Only the first and last point of fixation can be seen and along the saccadic pathway suppressed (Ripoll and Latiri, 1997). Therefore the first and last point is very important from visual acuity point of view. A table tennis player should change his accommodation as fast as his saccadic eye movements for his achievements. There is close relationship between accommodative system and vergence and binocular vision system (Griffin, 1988). Binocular vision improvement factors usually improve facility of accommodation and also binocular vision anomalies cause anomalies of accommodation (Pickwell, 1986). Table tennis improves binocular vision (Ripoll and Latiri, 1997) therefore; it may cause improvement of accommodation facility.

Another point that may explain improvement of accommodation facility in table tennis players is autonomic system. Accommodation controlled by autonomic system and recent study (Ferrauti et al., 2001) shows that autonomic system in tennis players may be more efficient. It seems all the above-mentioned factors may improve the facility of accommodation.

Acuity in reduced lumination is another skill that evaluated in this study. As it shown there is a significant (p < 0.01) differences between table tennis players and non-players. Visual acuity test is one of psychophysical tests. In psychophysical tests the respond of subject depends on peripheral and central nervous system, but perceptual centers involve prominently in the respond process. It seems perceptual systems are more efficient in champions. Other studies in racket-ball sports (Totterdell, 2000; Abernethy et al 2001; Fery and Crognier, 2001; Rowe and McKenna, 2001; Williams et al., 2002) show that sensory; motor and perceptual conditions in champions are more efficient than novice and non-players. An expert player should anticipate ball trajectory, direction of opponents' strokes, opponent's stroke movements, and opponent's pattern of play. Also temporal and spatial judgments of ball, environment and opponent in a short time should be done. And specific motor abilities for effective visual search must be considered for any successful player (Totterdell 2000; Abernethy et al., 2001; Ferrauti et al., 2001; Fery and Crognier, 2001; Rowe and McKenna, 2001; Williams et al., 2002). Naturally the above sensory, motor and perceptual advantage of elite may result better psychophysical performance of champions (Vergauwen et al., 1998).

Reduced lumination cause Purkinje shift. Visual acuity in Purkinje shift would be reduced (Boyce, 1973). As it shown in this study, better acuity can be seen in table tennis players than non-player in reduced lumination. According to this study and similar studies we can deduct that table tennis player can retain good visual acuity despite of unsuitable environmental conditions.

• That the ability of a champion depends on many sensory, motor and perceptual factors.
• Visual factors such as facility of accommodation and visual acuity in reduced lumination should be considered in table tennis players.
• Visual training may be useful for novice and also for experts.