BRAIN not needed: nerve signals are not necessary to control the muscles of a cat's pupil. A light-sensitive pigment in the iris can do the job instead.
Mammals were thought to rely on signalling between the eye and brain to resize the pupil and control the amount of light reaching the retina, but researchers at Johns Hopkins University discovered that eyeballs isolated from animals that are active at night or at dusk and dawn - including cats - continued to respond to light. They traced the effect to melanopsin, a light-sensitive pigment in the iris muscle.
The pigment plays a similar role in birds, fish and amphibians. It might provide dark-loving mammals with an additional pupil-shrinking tool that helps them avoid being dazzled if suddenly exposed to light.
See this report for more information on this intriguing finding.
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