The eyes of the chameleon provide 360 degree vision due to unique eye anatomy and an ability to transition between monocular and binocular vision.

Chameleons have a distinctive visual system that enables them to see their environment in almost 360 degrees (180 degrees horizontally and +/-90 degrees vertically). They do this in two ways. The first is with anatomical specializations that enable the eyes to rotate with a high degree of freedom. The second is the chameleon’s ability to transition between monocular and binocular vision, meaning they can view objects with either eye independently, or with both eyes together.

Several anatomical features enable chameleons to rotate their eyes to such a high degree. The eyes are located on opposite sides of the head, providing a view to the sides and behind or toward the front. Internally, the eye balls are mounted in twin conical turrets (like two upside down ice cream cones). Without a deep orbital socket to keep the eye from falling out (as in humans), the chameleon has evolved a thick, muscular lid. This lid surrounds each eye turret, leaving only the pupil exposed. This provides a “safety net” that enables the eye to bulge out of the conical turret. Without the restriction of a deep orbital socket, each eye can rotate nearly 180 degrees, giving a much wider range of vision than animals whose eyes are secured in socket structures.

The ability to transition between monocular and binocular vision also enables the chameleon to view objects panoramically. While searching for prey, the chameleon uses monocular vision, with each eye functioning independently of the other. The eye movements–or saccades–are referred to as ‘uncoupled’ when functioning this way. Two separate bundles of nerves control the musculature of the eyes, and two separate images are sent to the brain. Once the chameleon spots its prey, the saccades synchronize, in a process called “coupling,” and both eyes lock on the object. For coupling to occur, visual signals are first sent to the brain through two non-coupled neural bundles. The brain reads these signals, and the eye that has spotted the prey sends stronger electrical impulses to the brain than the eye still searching for the target. The neuron from the eye that does not see the prey syncs with the one that does, forming a larger neural bundle. Once the eye movements are synchronized, the eyes fix on the object and only the head rotates.

The chameleon’s ability to switch freely between synchronous and uncoupled saccadic eye movement is like having two movies playing in your head, and if you wanted to only watch one, you could. This enables the chameleon to operate as both a binocular and monocular organism in a remarkably efficient way for protection, food gathering, and reflexes.

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Angles of view for chameleon eyes. Source:
La morphologie du caméléon
This summary was contributed by Allie Miller.

Image: Tanalahy

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Last Updated September 14, 2016