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Experts' Eye View

Can the human eye detect an offside position during a football match?

BMJ 2004; 329 doi: (Published 16 December 2004) Cite this as: BMJ 2004;329:1470
  1. Francisco Belda Maruenda, specialist in family medicine (general practice) (
  1. 1 Centro de Salud de Alquerías, C/ R Fernández Miñarro, No 1, Alquerías, 30580, Murcia, Spain

    One of the most controversial rules in football is the offside rule. A possible explanation is that the human eye and brain are incapable of processing all the necessary visual information to apply the rule

    Football is regulated by rules. One referee and two assistant referees direct every game. When the rules are not applied correctly, the final result may be affected. This is often blamed on human error, but is this always true? In this review I analyse the physiology of the human eye to clarify if it is able to process all the information required to apply effectively one of these rules, the offside position.

    Eye physiology

    The eyes move to focus on objects and maintain them within their visual field. In doing so, they perform saccadic movements, smooth pursuit movements, vergence movements, vestibular movements, and accommodation.

    Saccadic movements

    Saccadic movements are rapid, brief, conjugate movements (that is, the eyes move as a pair).1 They occur when the eyes are inspecting an object, when the gaze shifts from one object to another, and during reading. They are necessary for locating objects rapidly in the fovea or for changing the depth of focus of the eye from one object to another within the visual field. This type of movement can be intentional or unintentional.2 Unintentional movements are prompted by an object entering the visual field or by the detection of movement.

    The latency from onset of the stimulus to onset of the saccadic eye movement is 200 ms, but this depends on the distance of the object, and a shorter interval may be possible.3 When the range of movement is greater than 10° the response time may increase. Other factors—type of stimulus, feature of stimulus, and observer's attention and age—may also affect the latency of saccadic movement.4 The speed …

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