Ethanol in the tear-film is one of the causes: it covers the surface of
the eye, disturbs the outer layer and favours evaporation of the aqueous
content of the tear, deteriorating the optical quality of the image we
see. The deterioration in vision is significantly greater in subjects
with breath alcohol content over 0.25mg/litre, the legal limit for
driving recommended by the World Health Organization
A study conducted by the University of Granada has demonstrated that
alcohol consumption markedly impairs night-vision because it increases
the perception of halos -- luminous circles -- and other visual
night-time disturbances. Moreover, this deterioration of vision is
significantly greater in subjects with breath alcohol content in excess
of 0.25mg/litre -- the legal limit for driving in Spain and other
countries and, also, that recommended by the World Health Organization
(WHO).
Researchers from the Laboratory of Vision Sciences and
Applications conclude that alcohol deteriorates the optical quality of
the image we see because, among other things, it disturbs the tear-film
that covers the surface of the eye. Essentially, this is because ethanol
from alcoholic drinks passes into the tear and disturbs the outermost
layer of the tear-film -- the lipid layer -- facilitating the
evaporation of the aqueous part of the tear. In an eye with a
deteriorated tear-film, the quality of the image that forms in the
retina also deteriorates, as the study shows.
In a
recently-published article in the international Journal of
Ophthalmology, the authors evaluate retina-image quality and
night-vision performance following alcohol consumption in a sample of 67
subjects. These volunteers had their breath alcohol content measured
with an evidential breath-alcohol analyser, supplied by the traffic
division of the Spanish Civil Guard in Granada. The participants
consumed different quantities of a prize-winning wine from the Pago de
Almaraes wineries, S.L. Benalúa de Guadix, Granada.
"Halometer" measurements
To
assess visual performance in low-illumination conditions, the
researchers used a visual test known as a "halometer," developed in the
Laboratory. This enabled them to quantify the level of night-vision
disturbance in the form of, say, halos around bright lights, perceived
by the subjects.
The results showed that
following alcohol consumption, the perception of halos and other
night-time visual disturbances increases and the optical quality of the
image the eye produces deteriorates. This is more marked in subjects
with a breath alcohol content level over the legal limit for driving,
that is, in excess of 0.25mg/l.
Principal author of the study,UGR
lecturer José Juan Castro, explains that "this research offers results
of value to society and public healthcare, especially in relation to
night-time driving. Alcohol consumption and low-illumination conditions
are factors present in many traffic accidents, hence people must to be
made aware of the effects of alcohol consumption, especially on vision."
In
fact, under these conditions, the perception of visual halos can make
it difficult for drivers to see a pedestrian crossing the road, to
distinguish a traffic sign, or they could be dazzled in some way by the
headlights of another car coming towards them.
Story Source:
http://www.sciencedaily.com
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