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The second set of factors which can modify the visual demand is related to the athlete:

-in several sports (such as ball, racket or fighting games), the athlete performs in dynamic conditions - that is in movement - , so not only needs he to keep his balance, but also he has his visual scene continually interrupted. On the contrary, in sports like motoring, as well as in target sports (archery, golf, etc), the athlete is still. Obviously, dynamic sports require those visual abilities that are in coordination with other sensory and motor functions;

-in some sports the athlete’s body position is influenced by the presence of a tool (cycling, motorcycling, etc), which has a great repercussion on the biomechanics, the aspect which deserves most attention. Besides, a bad posture may lead to physical weakness, which can have an effect on the visual performance by modifying the athlete’s sight angle. The position of the saddle, the handle-bar and the pedals, as well as the pursuit of a greater power expression and a better aerodynamics, force the cyclist to adopt a position which alters the spine profile (Zani, 2006).
The body is kept as parallel as possible to the ground, with the annulment of the lumbar lordosis, until the curvature takes the opposite direction. On the contrary, cervical lordosis will increase in order to allow the cyclist to have a good vision of the road.
This specific posture changes according to the type of activity which is performed; for example, it is more searched for on the racetrack than during a cross country running. Several are the effects of the posture on cycling (Zeri, 2007): the visual field, although not changing its width, spins from up to bottom; the "vision primary position" is kept thanks to an increase in cervical lordosis; finally, there is a greater need to raise one’s eyes. This latter point in particular can be crucial because the position of prolonged elevation can generate fusion and ocular motility problems.

Edited by Fabrizio Zeri, source: P.O. Professional Optometry, August 2008

The factors which can modify the visual demand are divided into 4 main groups: the ones which have to do with the visual information to process, those related to the athlete’s conditions, the environmental factors and the ones related to the game requirements.
The first group has to do with the visual target we are facing in the game. In football, for example, there is a ball, a door, opponents and team-mates, etc.
Each sport has its own visual targets, which differ according to various aspects:

-There are sports with static targets (generally, aim sports, such as archery, golf, etc.) and sports with dynamic targets (most of the sports, such as ball, racket or fighting games).
Obviously, dynamic visual abilities are not as important in the former as they are in the latter;

-The target size (let’s think about a hockey puck, compared to a basketball ball) demands a different level of acuity, so in some sports the optical correction, on which the acuity heavily depends, is pivotal;

-The target distance, and the dimension of the space within which the game is performed, require different focus demands: let’s think about the ping-pong table (measuring 2,74 meters for 1,52) and the regatta field during the ‘American’s Cup.
In most of the sports, the critical element is not the target distance, but its continuous variation in position, which demands for a good flexibility in accommodation;

-The target position is really important because it can call for central or peripheral attention, as well as both (Erickson, 2007).
A football player must always keep an eye on the ball (the central target), but he must also keep opponents and team-mates under control with the corner of his eye (peripheral vision), which a biathlon shooter is not obliged to do.

Edited by Fabrizio Zeri, source: P.O. Professional Optometry, August 2008

Visual performance is made up of several visual abilities, which can be divided into: basic functions, visual-motor functions and perceptive processes.
By studying the visual system of selected athletes, in comparison with non-athletes’ one, it has emerged that some abilities contribute more than others to enhance an athlete’s motor performance.
In fact, the importance of the different visual abilities is related to the task required by a specific sport and the conditions in which it is performed. For example, the visual requirements for a skier, involved in a downhill race in a cloudy and misty day, will be completely different from the ones for a golf-player who is about to hit the ball on the green in a beautiful sunny day. Every sport has its own setting of specific rules, tools and environmental conditions, that is elements which can modify the visual demand.
To analyse the visual demands of the single athlete, involved in a specific sport, is the first important step for a vision expert to improve the sportsman’s visual performance (Erickson, 2007).

Edited by Fabrizio Zeri, source: P.O. Professional Optometry, August 2008