The transparent scale covering each eye of a snake is called the brille.
The brille, also known as the spectacle, ocular scale, or eye cap, is a modified scale that protects the eye. Because snakes do not have movable eyelids, this fixed covering helps shield the eye from dust, soil, and injury while still allowing light to enter.
The brille is continuous with the surrounding skin and is shed when the snake molts. Before shedding, fluid often builds between the old outer layer and the new skin, making the eyes look cloudy. This temporary condition is commonly called being in the blue.
The brille is not the same as a contact lens or a separate eyelid. It is an external scale, and a retained brille after shedding can cause problems if it is not naturally removed. Most snakes have this eye covering, although its appearance varies among species.