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Unlike yesterday's treatment in Voice Recognition ≠ Speech Recognition, the terms, "iris" and "retina" are in no way up for grabs.
The iris (left), which gives people "eye color," controls how much light enters the eyeball. The retina (right) is the structure laying along the inside, back surface of the eyeball that translates light into nervous impulses for the optic nerve to send to the brain.
In a camera analogy, the iris would be, well, the iris, since cameras have them, too. The retina would be the film, or in an even better digital analogy, the charge-coupled device (CCD) that translates light into ones and zeros for computer chips.
Both iris and retina are used as biometric modalities in identity management applications.
Iris biometrics match the iris's unique surface features (similar to fingerprints). Retina biometrics use eye's vascular network for matching.
Retinas have been in use as a biometric identifiers for far longer than iris (1984 vs 1995), but using the iris is far more common today. This is because using the iris makes for cheaper and easier identifications.
For more on the subject, I recommend this [ed: inactive link removed]. It was written in 2006. Both technologies will have improved since then, but iris technologies have improved faster.
