The question of whether lizards blink has a complex answer rooted in their diverse anatomy. Blinking is a natural mechanism for cleaning and moisturizing the eye’s surface, protecting it from debris and desiccation. While many lizard species perform this action, a significant number have evolved alternative methods for maintaining eye health.
Anatomy Determines the Answer
Lizard species are broadly divided into two groups based on their ocular structure: those with movable eyelids and those without. Lizards that blink possess separate upper and lower eyelids, much like humans, allowing them to close their eyes for protection or sleep. This structure enables the rapid distribution of lubricating tears and the mechanical removal of foreign particles. Many other lizards lack these movable palpebral folds entirely. In these species, the upper and lower eyelids have fused together across the surface of the eye during development.
How Lizards Without Eyelids Maintain Eye Health
For lizards that do not blink, their fused eyelids form a transparent, protective scale called the “spectacle” or “brille.” This structure acts like a permanent, built-in contact lens, offering constant protection from dust, sand, and minor physical trauma. The spectacle is part of the lizard’s skin and is shed along with the rest of the body during the molting process. Because the eye is permanently covered, these lizards appear to stare unblinkingly. They maintain moisture and clean the spectacle by using their long, mobile tongues to periodically lick the surface. This tongue-wiping action clears away accumulated dust and debris, acting as a tear distribution system, while the subspectacular space beneath the scale is kept moist by fluid secreted from the Harderian gland.
Lizards That Blink
Lizards with movable eyelids blink similarly to many other vertebrates, using the action to lubricate the cornea and shield the eye from sudden threats. This group includes numerous common species such as monitor lizards, iguanas, and chameleons. Their blinking mechanism often includes a specialized structure known as the nictitating membrane, or “third eyelid.” This translucent membrane sweeps horizontally across the eye, usually from the inner corner outward. The nictitating membrane provides rapid protection and moisture distribution while still allowing the lizard to see through it. In some lizards, blinking can be a complex action involving the lower lid moving upward, the eyeball retracting slightly into the socket, and the nictitating membrane drawing across the eye. For species that live in open habitats, this ability to quickly close the eye provides a swift defense against airborne particles or predators.