A Good Name For An Album; Always Open.
Snakes do not have eyelids, so they don’t blink. Instead the lower and upper eyelids have fused to form the ocular scale. This appears as a thin clear membrane protecting and covering the cornea. These are called spectacles or brilles. Brille is a Germanic word meaning spectacle, it also means bright or clear in Spanish. So they can not blink or close their eyes in any way. This probably gave rise to the myth that they can hypnotise with their unbreaking gaze. Some, like the grass snake have round pupils, while others like the adder have vertical-slit pupils.
Spectacles or Contact lenses?
The vast majority of Snakes live close to or in the ground, with many also being arboreal tree dwellers. As they move around they can get dust, grit and vegetation in their faces and eyes. The spectacles protect the corneas from damage. The thin brilles are not in contact with the corneas but are separated by fluid that moisten the eyes, similar to our tears. So in answer to the above question, they are more like spectacles than contact lenses.
Show no emotion
All reptiles produce tears. The fluid between the retinas and the spectacles is produced by tear glands behind the lenses. A pair of nasolacrimal ducts drain the tears into the mouth. The tears can not flow from the eyes down the cheeks as they do in crocodiles, turtles or humans because the spectacles are attached. This is why snakes cannot cry.
Losing Your Glasses
Because snake spectacles are part of the skin, they are lost when the snake sheds its skin. Prior to shedding or sloughing, snakes’ eyes become milky-looking as the snakes secrete an opaque fluid between the old skin and the new skin to aid shedding. When in this condition the snakes are vulnerable to being caught by predators as their vision is impaired. They become more nervous as they feel incapacitated.
For the keen-eyed spotter a slow-worm can blink which gives it away as being a lizard and not a snake or a worm and in warm weather they aren’t slow either. Who on earth named them?
John R Grundy
Revealing Reptiles Project Officer