The Nikon MicroscopyU confocal microscopy image gallery was created with a PCM-2000 confocal scanning system interfaced to a Nikon Eclipse E600 upright microscope. Images were recorded in successive z-axis serial sections with C-Imaging Systems software with excitation illumination provided by an argon-ion and/or a helium-neon laser.

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View a higher magnification confocal sequence of a frog eye.

Frogs have eyes that closely coordinate with their long sticky tongues to enable these amphibians to capture fast moving prey with whip-like accuracy. A majority of species possess eyes that bulge from the sides of their heads so that most frogs can see in almost all directions. However, frogs are naturally nearsighted and are only able to focus on objects that are passing close by or flying within a distance of six inches. Frogs reduce the amount of light that enters their eyes by closing their pupils into narrow slits. Although they have protective clear membranes that can cover the eye surface (termed the cornea) these creatures have poorly developed eyelids that do not close during resting periods. Instead, frogs typically withdraw their eyes into sockets located within their skulls. Frogs also use their eyeballs to help push food down their throats by retracting each eye, usually one at a time, into the sockets.

The attention span of a frog is very limited and dictated by the portion of the internal eye structure called the retina. This layer of neural tissue, located in the rear section of each eye, relays visual messages to the brain. Highly specialized light-sensitive cells in the retina of the frog fire (or release neurotransmitters) only when stimulated by shapes and movements that resemble edible insects, such as flies and worms. Because the nerves in the eye do not release the chemicals unless the object is moving, a frog can starve even if surrounded by tasty bugs, so long as the insects are quiet and do not move. Much of the information that a frog requires to activate the flick of its sticky, whip-like tongue is processed in the retina. By contrast, other animals typically process visual information in special centers located within in the brain. Because the brain of the frog has fewer steps to process, the signal to retrieve the edible morsel can be transferred more expediently to the tongue, resulting in a successful hunt.