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292 Biomimetics: Biologically Inspired Technologies

offer a survey of the ever-increasing attempts to reconstruct biological eyes. They are roughly
divided by the general classifications of the eyes they seek to replicate; that is, they are separated
into biomimetic camera (single lens) eyes, compound eyes, and others.

11.2 CAMERA EYES

Certainly the most familiar example, the human eye is but one of many forms of camera-type eyes
and generally relies on a single lens to focus images onto a retina for image acquisition. The lens
material properties, structure, and focusing mechanism vary from organism to organism. For
example, some amphibian species have eyes which accommodate by moving a lens closer or
farther to the retina. By contrast, the human eye adjusts the curvature of the lens itself to accomplish
the same task. Birds have the added benefit of being able to reshape the cornea as well as the lens for
accommodation. Some of the various camera eye designs are shown below (Figure 11.1).
These natural eyes have provided the inspiration for a number of optical systems with specific
capability requirements. These include different approaches for adaptive optics, efficient image
processing, and size-constrained wide-angle views.

11.2.1 A Fluidic Adaptive Lens

Some forms of camera eyes, oftentimes in amphibious animals, use hydraulics to adjust their focal
lengths. A chamber behind the lens is filled or emptied with fluid depending on the desired focus
(Figure 11.2). One example of this is the whale eye, where this design allows for good vision both
in and out of the water. In addition, the fluid also compensates for increased pressure at deeper
aquatic environments.

Spherical gradient lens
Cornea
Lens
Retina
Ciliary muscle

Mammal Eye Fish Eye

Cramptons's muscle
Bony ossicle Bony ossicle Protractor lentis

Brucke's muscle Brucke's muscle

Reptile Eye Bird Eye Amphibian Eye
Figure 11.1 (See color insert following page 302) Various types of camera-type eyes. The arrangement of the
mammalian ciliary muscle allows for passive changes in lens thickness. Brucke’s muscles attached to bony
ossicles in reptiles and birds, on the other hand, actively change the lens thickness. Birds have an additional
muscle, Crampton’s muscle, which can alter the shape of the cornea. The protractor lentis in some amphibian eyes
moves a fixed-shape lens closer to or farther from the retina for accommodation.