The Pupil is located
in the centre of each eye in the human body.
It generally appears to be the dark "centre"
of the eye, but can be more accurately described as the circular aperture
in the centre of the
iris through
which light passes into the eye.
The size of the pupil (and therefore the amount of light that is admitted
into the eye) is regulated by the pupillary reflex (also
known as the "light reflex"). That is, when bright light reaches the
retina, nerves of the parasympathetic nervous system are stimulated,
a ring of muscle around the margin of the iris contracts, the size of
the pupil is reduced, hence less light is able to enter the eye. Conversely,
in dim lighting conditions the pupil opens due to stimulation of the
sympathetic nervous system that contracts of radiating muscles, hence
increases the size of the pupil.
Note that although some animals' eyes
are basically structured in a similar way to human eyes, they
may appear to be very different.
E.g. Differently shaped pupils of cats compared with people.
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The subject of visual (also known as "physiological")
optics is a key component of many courses within the fields of
both biology and physics. It is also an essential consideration
in the design of displays and control units used in many applications
from
televisions
and mobile telephones to advanced aircraft. In the context of engineering
"visual optics" is one of several medical and psychological topics in
the important area of "Human Factors".
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