Snakes cannot close their eyes like humans or other animals. They do not possess movable eyelids. Instead, their eyes are permanently covered by a transparent, scale-like structure. This unique adaptation means a snake’s eyes always appear open, even when resting or sleeping. This design provides constant protection without the need for blinking.
The Snake’s Unique Eye Covering
Instead of eyelids, snakes have a specialized, clear scale called a “spectacle” or “brille” fused over each eye. This transparent covering is a permanent part of the snake’s skin and does not move. The spectacle acts as a protective barrier, shielding the delicate eye surface from debris, dust, and potential injuries. During embryonic development, snake eyelids fuse and become transparent, forming this protective spectacle. A small space between the spectacle and cornea contains tear-like secretions that lubricate the eye for smooth movement.
How Snakes “Sleep” and Protect Their Eyes
Since snakes cannot close their eyes, they do not “sleep” by shutting their eyelids like mammals. However, snakes do enter periods of rest and reduced brain activity, which is their form of sleep. During these times, their eyes remain open, allowing for continuous vigilance. The spectacle serves as a constant shield, preventing foreign objects from irritating or damaging the eye, even during deep rest. While they cannot block out light, some research suggests snakes can control blood flow to their spectacles, potentially influencing vision clarity during different states like relaxation or perceived threat.
Shedding and Eye Health
The spectacle is an integral part of a snake’s skin and is shed along with the rest of its outer layer during ecdysis. Before shedding, the old spectacle detaches from the new one forming underneath, which can cause the snake’s eyes to appear cloudy or milky, often described as “in blue.” This temporary cloudiness can impair the snake’s vision, making them more reclusive and sensitive. A healthy and complete shed is important for clear vision, as a new, transparent spectacle is revealed once the old skin is fully removed. If the spectacle does not shed properly, a condition known as retained eye caps can occur, potentially affecting the snake’s eyesight and requiring assistance.