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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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