Vision in Sports

Vision is the process of seeing and perceiving the surrounding  environment  by  using  information contained  in  light.  Appropriate  visual  information  is  imperative  for  almost  every  sporting  task to  ensure  that  athletes  are  able  to  monitor  the actions of others, while also perceiving their position in relation to targets, such as balls, nets, and walls,  and  the  playing  environment.  In  considering  vision  in  sport,  this  entry  discusses  what  the important  characteristics  of  vision  are,  whether elite  athletes  rely  on  better  vision  than  others, and whether vision training can enhance sporting performance.

The Important Characteristics of Vision

Vision is a phenomenon not simply isolated to the eyes. While the ability to see commences at the eye when  the  cornea  and  crystalline  lens  focus  light onto the retina at the back of the eye, vision encapsulates  a  complex  procedure  that  relies  on  how the brain perceives this array of light. When light is  focused  on  the  retina,  a  complex  collection  of neural signals is relayed via the visual pathway to the  visual  cortex  in  the  brain.  The  visual  cortex is  located  in  the  occipital  lobe  at  the  back  of  the brain;  it  processes  and  combines  the  visual  information from the two eyes and conveys this information  onward  via  a  complex  communication network  that  both  controls  action  and  facilitates perception of the surrounding environment.

There  are  many  different  measures  that  can be  used  to  characterize  vision.  Humans  have  the capacity  to  perceive  their  surrounding  environment  clearly,  with  color,  across  a  wide  range  of lighting conditions and regardless of whether they themselves  or  objects  within  the  environment  are stationary or moving. As a result, an evaluation of an athlete’s vision can encompass a diverse range of characteristics, sometimes referred to as general visual measures or basic visual functions.

A considerable number of different visual measures  have  the  potential  to  impact  performance in  sport.  Consequently,  it  is  recommended  that athletes have their vision tested regularly (usually every 2 years) to ensure that any problems can be corrected  to  prevent  them  from  adversely  affecting  on-field  performance.  Following  are  some  of the  more  important  visual  measures  relevant  for athletes.

Visual Acuity

Visual  acuity  (VA)  measures  the  ability  of  the eye to resolve detail. It is typically evaluated using a  letter  chart,  and  is  measured  by  means  of  the Snellen fraction (e.g., 6/12 or 20/40; the first number in the fraction is the test distance, conventionally 6 meters or 20 feet, and the second colloquially refers  to  the  distance  a  person  with  “normal” vision could resolve the same detail). Static visual acuity  refers  to  the  ability  to  resolve  detail  in  a stationary  target,  and  is  the  measure  most  commonly used to assess vision. Dynamic visual acuity is occasionally tested in sport-specific assessments of vision to evaluate the ability to resolve detail in a  moving  target.  Deficiencies  in  VA  are  common in  athletes;  they  are  most  frequently  caused  by myopia (poor distance vision) or hyperopia (poor or effortful near vision), and are usually corrected using spectacles or contact lenses.

Contrast Sensitivity

Contrast sensitivity reflects the ability of the eye to resolve differences in brightness. Poor contrast sensitivity  is  likely  to  influence  an  athlete’s  ability to see at night or in dim conditions. Contrast sensitivity declines with age and otherwise is most commonly hampered by cataracts (clouding of the crystalline  lens)  and  diabetic  retinopathy  (retinal disease as a result of diabetes).

Peripheral Vision

Peripheral vision is the ability to see objects that are located away from the direction of gaze. The binocular  field  of  vision  extends  approximately 190  degrees  horizontally  and  130  degrees  vertically, though the clarity of objects decreases as they move further from the center of the visual field. A restriction  of  peripheral  vision  will  limit  an  athlete’s  ability  to  identify  or  monitor  other  players or objects that are located in side vision; however, restrictions to peripheral vision are relatively rare and  usually  only  occur  in  the  latter  stages  of  life as a result of conditions like glaucoma (damage to the optic nerve at the back of the eye) and stroke.

Depth Perception

Depth  perception  is  the  ability  to  perceive  the distance  to,  or  between,  objects  in  space.  It  is particularly important in sporting tasks where an athlete  must  hit  or  interact  with  moving  objects. The perception of depth is a complex process that relies on specific information from each eye and on the comparison of relative information from both eyes.  Accordingly,  depth  perception  can  be  particularly poor when one eye is notably worse than the other (common in individuals with an eye turn or who have experienced an injury to one eye).

Color Vision

Color  vision  refers  to  the  ability  to  perceive different wavelengths of light that are seen as different shades of color. Deficiencies in color vision are usually a result of genetic inheritance, meaning that they are not normally curable. Approximately 8% of males and 0.5% of females experience problems with color vision. The most common form of deficiency  causes  difficulties  when  discriminating between red and green colors; this has been shown to  be  a  problem  when  performing  some  sporting tasks.

Eye Movements

Six extraocular muscles control the direction of each eye to ensure that central vision can be used to resolve objects of interest with the best possible clarity.  Skilled  athletes  use  very  specific  and  efficient eye movement strategies to direct their gaze toward the most informative areas in their visual field and to track and predict the future location of moving  objects.  Neuromuscular  conditions  such as multiple sclerosis and strabismus (an eye turn) can affect the ability of athletes to make fast and accurate eye movements.

Do Elite Athletes Have Better Vision Than Other People?

The remarkable skill level of elite athletes has led some  to  wonder  whether  these  achievements  are underpinned  by  some  sort  of  extraordinary  or above-normal level of visual skill. Vision is unmistakably  important  for  the  successful  performance of  many  different  sporting  tasks,  and  for  this reason  it  may  be  intuitive  to  infer  that  superior vision may lead to superior sporting performance. However, there has been, and continues to be, considerable  debate  about  whether  skilled  athletes have better vision than lesser skilled athletes, and so far the evidence has been somewhat equivocal.

Two   key   methods   have   been   employed   to compare  the  vision  of  skilled  and  lesser  skilled sportspeople.  The  first  involves  epidemiological studies  that  evaluate  the  relative  prevalence  of visual problems in athletic and nonathletic populations. These studies typically conclude that athletes have a lower (or sometimes similar) prevalence of visual  problems  than  non-athletes.  In  essence  this supports the view that, on average, skilled athletes have  better  vision,  but  it  more  likely  reflects  the lower likelihood that people with poor vision take part in (or are successful at) sporting activities. The second method of investigation directly compares specific visual attributes like VA and contrast sensitivity across different levels of sporting expertise. Although the evidence is equivocal whether these attributes  can  differentiate  players  of  contrasting skill  levels,  a  growing  number  of  studies  suggest this may not be the case.

Multidisciplinary   examinations   of   sporting expertise  have  provided  a  useful  means  of  establishing  the  relative  contribution  of  general  visual measures when compared to other factors that can predict  sporting  skill.  These  analyses  have  generally concluded that sport-specific perceptual skills, such  as  anticipation,  pattern  recall,  and  decision making, are much better for discriminating skilled and lesser skilled athletes than primary visual attributes can. Although for some there is a prevailing view  that  skilled  sportspeople  are  characterized by  superior  visual  attributes,  there  appears  to  be an  increasing  recognition  that  sport-specific  measures of perceptual–cognitive skill are more likely than general visual measures to be associated with sporting success.

Can Vision Training Enhance Sporting Performance?

There is considerable debate questioning whether vision  training  can  be  used  to  improve  on-field performance.  This  question  requires  a  consideration of three key questions.

Is Vision a Limitation to Performance in Sport?

Vision  is  clearly  important  for  success  in  most sporting  tasks;  if  any  visual  characteristic  were to   progressively   become   worse,   it   is   reasonable to assume that at some level each is capable of  adversely  influencing  on-field  performance. What  is  less  clear,  though,  is  at  what  point  each of  these  characteristics  may  start  to  impinge  on sports performance. For example, if VA was to be systematically  decreased  to  the  point  of  practical blindness,  evidently  performance  must  decrease at  some  point.  In  essence,  most  vision  specialists would advocate that normal visual function is necessary for most favorable on-field performance. As a result, any decrease below the normally expected capacity  would  lead  to  a  commensurate  decrease in  performance.  The  small  subsection  of  sports vision  specialists  who  claim  that  skilled  athletes rely on better-than-normal vision to underpin their sporting  success  infer  that  even  a  normal  level of  visual  function  limits  performance,  and  that improvements in vision to supranormal levels lead to enhanced sporting performance.

Can Vision Be Improved by Training?

Spectacles  and  contact  lenses  are  used  to  correct  the  most  prevalent  of  visual  problems  (e.g., myopia  and  hyperopia);  however,  clear  evidence exists to show that vision training can be used to improve  other  visual  characteristics,  such  as  eye movements and visual focus. Importantly though, this  training  is  typically  used  to  help  those  with visual problems. While vision training may be useful  to  help  athletes  with  these  types  of  problems, it is not at all clear whether training can facilitate supranormal  vision.  Even  if  normal  vision  is  a limitation  to  sporting  performance,  there  is  very little evidence to suggest that visual characteristics can be enhanced to levels superior to those found in the general population.

Do Improvements in Vision Result in On-Field Improvements in Performance?

Vision  training  is  frequently  used  to  improve the  ability  of  individuals  to  perform  activities  of everyday living. For example, training can lead to direct  improvements  in  the  performance  of  visually  dependent  tasks  like  reading  and  computer use  by  correcting  deficiencies  in  gaze  and  focusing. Similarly, there is good reason to believe that sporting performance should be improved if vision training  can  correct  visual  deficiencies  that  limit on-field performance. However, there is very little evidence to suggest that the vision of athletes can or  should  be  trained  to  above-normal  levels  of operation,  or  equally  that  generalized  training  of a  range  of  different  visual  measures  can  lead  to improvements in athletic performance.

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