Snakes control blood flow in their ‘eyelids’ to help them see
by Bethany Brookshire
Snakes have blood flowing over their eyes. Technically, you do, too. But in your case, that blood is contained within the tiny blood vessels that send oxygen and nutrients to your eyelids. Eyelids that blink keep us from being blinded by the blood vessels and tissues making up our eyelids, while still allowing the eyelid to do its job. When you blink, your eyelids help keep dust and debris out of your eyes while keeping the surface moist.
Snakes aren’t so lucky. Instead of eyelids, snakes have what is known as a spectacle, an analogous piece of tissue. While our eyelids move, the snake spectacle is fused together. While this does help keep debris out of the eye and keeps the eye moist, it means that snakes have a tissue in front of their eyes. A tissue full of blood vessels, that never goes away. Instead, it acts like a window, and the snake’s eye can move freely underneath.
Now, this might seem OK. But blood vessels, you see, are solid little things. You can’t exactly see though them. So even though the blood vessels in the spectacle might be tiny, that close to the eye, they could interfere with what the snake is trying to see (like how you sometimes see “floaters” from the structures within your own eye). Blinded by its own blood.
|