Increase of the spatial resolution and of the contrast sensitivity for myosis induced in usual drivers demonstrates experimentally.
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2009
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Gómez Tortuero, E.
Colilla, E.
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Abstract
Human visual system is able to adapt itself to get better visual perception in a very extense lighting range, since light of the moon until brilliant sunlight, so from scotopic until photopic lighting (Walkey and Barbur, 2006).
Changes in pupil size produced in response to changes in light intensity optimise the amount of light received by the retina, maximizing visual perception. This is produced along 10 log units, thanks to the human eye adaptation by biochemical and nervous mechanisms. In the light/darkness process of adaptation mechanical activity, due to pupil size variations (Myosis/mydriasis), contributes 1 logarithmic unit and is the most rapid of all contributions to the response. Between both lighting limits (photopic and scotopic), mesopic range is establised. This lighting (mesopic) is found in a natural way when night falls or at dawn, time in which driving becomes a harder task, thus its study has such an enormous interest due to its influence of driving.
Mesopic vision describes the period of trnsition from rods (Scotopic) until cones (photopic) vision, in which both photoreceptors contributes to the visual response. Although it hasn´t been precisely establised by the CIE (Commission Internationale de l´Eclairage), mesopic range covers roughly 4 log units (Wyszecky y Stiles 1982; Walkey et al. 2006), which means lighting levels frecuently used in occupational ambient.
In mesopic lighting condition several changes are produced in visual function. Pupil size variations distort the optic of the eye, degrading the quality of the retinal image (aberrations and light dispersion). On the other hand, the extensive spatial summation of the rods signal increases the light sensitivity but also causes a significant lost of contras sensitivity, the visual acuity of low contrast and the spatial resolution (Walkey y Barbur, 2006).