Snakes have a unique mechanism that optimizes their vision-they do it by controlling the blood flow in their spectacle, a new study revealed.
Kevin van Doorn, PhD, and Professor Jacob Sivak, from the Faculty of Science, found that the coachwhip snake's visual blood flow patterns change depending on what's in its environment.
"Van Doorn, from the School of Optometry and Vision Science, said that each species' perception of the world is unique due to differences in sensory systems," said.
Instead of eyelids, snakes have a clear scale called a spectacle. It works like a window, covering and protecting their eyes.
Spectacles are the result of eyelids that fuse together and become transparent during embryonic development.
When van Doorn was examining a different part of the eye, the illumination from his instrument detected something unusual.
Surprisingly, these spectacles contained a network of blood vessels, much like a blind on a window. To see if this feature obscured the snake's vision, van Doorn examined if the pattern of blood flow changed under different conditions.
When the snake was resting, the blood vessels in the spectacle constricted and dilated in a regular cycle. This rhythmic pattern repeated several times over the span of several minutes.
But when researchers presented the snake with stimuli it perceived as threatening, the fight-or-flight response changed the spectacle's blood flow pattern. The blood vessel constricted, reducing blood flow for longer periods than at rest, up to several minutes. The absence of blood cells within the vasculature guarantees the best possible visual capacity in times of greatest need.
Next, the research team examined the blood flow pattern of the snake spectacle when the snake shed its skin. They found a third pattern. During this time, the vessels remained dilated and the blood flow stayed strong and continuous, unlike the cyclical pattern seen during resting.
The study has been published in the Journal of Experimental Biology.