Brille

The brille (also called the ocular scale, eye cap or spectacle) is the layer of transparent, immovable disc-shaped skin or scale covering the eyes of some animals for protection, especially in animals without eyelids.

In snakes, there are no eyelids and the brille is clear and cannot be distinguished, except when the animal is becoming ready for ecdysis.

When the snake moults, the brille is also shed, generally inside out, as part of its skin.

The brilles protect their eyes from dust and dirt and give them a "glassy-eyed" blank appearance.

[3] Some reptiles, mammals and birds have a translucent third eyelid that moves horizontally across the eye called the nictitating membrane.