The role of retinal adaptation in night driving.
OBJECTIVE
Driving is essentially a visuomotor task, and there is now compelling evidence that the disproportionate number of road accidents under night driving conditions is linked to changes in visual performance resulting from reduced lighting. The objective of this article is to establish the extent to which vision is either rod-or cone-dominated under night driving conditions.


METHODS
Visual thresholds are measured under lighting conditions that simulate urban lighting. Dark adaptation curves are obtained under three ambient lighting conditions ranging from low (0.1 cd/m) to high (5 cd/m) mesopic levels of retinal adaptation using circular discs of different sizes (1 degree, 2 degrees, 3 degrees, and 5 degrees) presented at retinal eccentricities of 0 degrees, 10 degrees, 20 degrees, 30 degrees, and 40 degrees.


RESULTS
The dark adaptation curves exhibit the classic inflection point between rod and cone activity for the lower levels of ambient illumination but a simple monophasic function for the high mesopic levels (>0.5 lux). Adaptation rates are four times faster for the higher compared with the lower illumination level and twice as fast for central compared with peripheral presentation.


CONCLUSIONS
The data suggest that vision is mediated by cone pathways at 5 lux and by rod pathways at 0.5/0.1 lux. This shift does not profoundly affect sensitivity, but because rod pathways are known to be slower than cone pathways, it will certainly affect observers' ability to respond to rapidly changing viewing conditions such as are encountered when driving at night.
Plainis
Sotiris
S
Vardinoyiannion Eye Institute of Crete, Department of Ophthalmology, School of Medicine, University of Crete, Heraklion, Crete, Greece. plainis@med.uoc.gr
Murray
Ian J
IJ
Charman
William N
WN
D000328:Adult; D001334:Automobile Driving; D003623:Dark Adaptation; D004867:Equipment Design; D006801:Humans; D008029:Lighting; D009885:Ophthalmology / Q000295:instrumentation; D010775:Photic Stimulation / Q000379:methods; D012160:Retina / Q000502:physiology*; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology; D012684:Sensory Thresholds; D013997:Time Factors; D014785:Vision, Ocular / Q000502:physiology