November 5, 2013
Snakes Can Control Blood Flow To Their Eyes When A Threat Is Perceived
April Flowers for redOrbit.com - Your Universe Online
Snakes can optimize their vision when they perceive a threat by controlling the blood flow to their eyes, according to a new study from the University of Waterloo.
The coachwhip snake's visual blood flow patterns change depending on what is in its environment, according to Kevin van Doorn, PhD, from the School of Optometry & Vision Science, and Professor Jacob Sivak, from the Faculty of Science.
“Each species' perception of the world is unique due to differences in sensory systems,” said van Doorn, from the School of Optometry & Vision Science. The study results were published in the Journal of Experimental Biology.
Snakes have a clear scale called a spectacle instead of eyelids. This scale works like a window, covering and protecting their eyes. The spectacles are created during embryonic development as eyelids fuse together and become transparent.
Van Doorn was examining a different part of the snakes' eyes when the illumination from his instrument detected something unusual.
The spectacles contain a network of blood vessels, Van Doorn found, much like blinds on a window. He examined the pattern of blood flow changes under different conditions to see if the vessels obstructed the snake's vision.
The blood vessels constrict and dilate in a regular cycle during the snake's resting period. Over the span of several minutes, this rhythmic pattern repeated several times.
When presented with threatening stimuli, however, the snake's fight-or-flight response changed the spectacle's blood flow pattern. The vessels constricted and kept the blood flow reduced for longer periods than during rest - for up to several minutes at a time - guaranteeing the best possible visual capacity in times of greatest need.
“This work shows that the blood flow pattern in the snake spectacle is not static but rather dynamic,” said van Doorn.
As a next step, the researchers examined the blood flow pattern of the snake spectacle when the snake shed its skin - finding a third pattern. During shedding, the vessels remained dilated and the blood flow stayed strong and continuous, unlike the cyclical pattern observed during resting.
The results reveal the relationship between environmental stimuli and vision, as well as illuminating the interesting and complex effect blood flow patterns have on visual clarity. Further investigations are needed to explore the underlying mechanism of this relationship.
“This research is the perfect example of how a fortuitous discovery can redefine our understanding of the world around us,” said van Doorn.