PubMed · 15440041
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K H MacPHERSON. 1950-08-01. Visual standards for safe driving.. https://pubmed.ncbi.nlm.nih.gov/15440041/
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Is it possible for a driver to compensate for visual field defects by skill along with eye and head movements? Monocular field defects with a normal second eye are no problem, because a normal binocular visual field is adequate for all areas of traffic. A total bitemporal hemianopia creates a special situation, because the patient loses a three-dimensional space behind a vertical line through the point of fixation. He may have no binocular visual field. In this case the ability to participate in certain traffic situations may be limited with reduced risk profile. A real problem is posed by defects in the binocular visual field, e.g., due to lesions of the suprachiasmal visual pathway or due to ocular diseases causing damage to both eyes (e.g., glaucoma, diabetic retinopathy, etc.). Such defects usually cannot be compensated for, neither by skill nor by eye or head movements. Saccadic eye movement training and other procedures are only of limited help. These procedures may provide some compensation for daily use; a complete restoration of the ability to participate in traffic is not possible. Rare exceptions may be patients with damage to the visual pathway acquired peri- or postnatally or in early childhood when there is still enough plasticity in the visual system to develop mechanisms of compensation by completely changing the system of eye and head movements.
Peripheral vision is very important for visual perception in all fields of traffic. The central visual field is most important because the major part of information input occurs here. The peripheral parts of the visual field have excellent motion detection and the capability to perceive flicker stimuli. In addition to the central visual field the horizontal parts to the left and right are important, especially for road traffic. Information input occurs in a continuous sequence of saccadic eye movements which transport critical objects into the fovea. After fixation, the observer analyses the object and decides whether or not a reaction is necessary. Triggering of a saccadic eye movement only can occur if the critical object is suprathreshold in size, contrast, colour, motion and temporal modulation. This is the reason why perception of peripheral objects needs more time than the perception of objects in the fovea. Without an intact central and peripheral visual field participation in traffic is not possible.
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