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Astigmatism
Name: Denise P.
Status: Educator
Age: 40s
Location: N/A
Country: N/A
Date: March 2004
Question:
Astigmatism: is it considered a dominant recessive trait,
or is it just a visual anomaly that is not caused by a gene? And please
explain how.
Replies:
Astigmatism is probably just a visual anomaly not caused by a gene, at
least that we know. My guess anyway.
Astigmatism is a label given to particular way that the eye's lens is
not perfect. We could imagine a "perfect" lens, one which gives a
perfect image of what you are looking at, and then start adding
deformations in various ways. For example the curvature of the lens
could be different between the top and the bottom. The curvature might
not be enough, or might be too much.
But in real life you might have several of these at the same time.
People have developed a cataloging system for this and given the errors
in the lens names like astigmatism, spherical aberration, distortion,
coma. Again each is sort of an idealized error term. But eye doctors
try to correct for the first two -- they give you a lens with a certain
power (far sighted/ near sighted), and they also try to correct
astigmatism -- that this power might be greater say horizontal than it
is say vertical. They do this by adding a slight cylindrical shape to
your glasses -- cylinders are like bowls, but have a certain axis, or
direction to them.
PF
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