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biscuit
medicine forum Guru Wannabe
Joined: 24 Apr 2005
Posts: 296
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 Posted: Mon Jul 17, 2006 11:12 pm Post subject:
Contacts for astigmatism
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For astigmatism, especially if using RGP type lenses, it seems like you
could build the backside of the lens to fairly precisely match the
shape of the cornea. With it like this, the lens would suck in to the
cornea in a known orientation, so rotation would not be an issue
(assuming enough corneal astigmatism, and thin enough tear layer).
With that, the outer surface of the lens could be built to provide the
desired correction.
Why is this a bad idea? I assume someone has thought of it. Is it
just too hard to manufacture super custom lenses like that?
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Quick
medicine forum Guru
Joined: 19 Jun 2005
Posts: 343
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| Posted: Mon Jul 17, 2006 11:54 pm Post subject:
Re: Contacts for astigmatism
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Charles wrote:
| Quote: | For astigmatism, especially if using RGP type lenses, it
seems like you could build the backside of the lens to
fairly precisely match the shape of the cornea. With it
like this, the lens would suck in to the cornea in a
known orientation, so rotation would not be an issue
(assuming enough corneal astigmatism, and thin enough
tear layer). With that, the outer surface of the lens
could be built to provide the desired correction.
Why is this a bad idea? I assume someone has thought of
it. Is it just too hard to manufacture super custom
lenses like that?
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My doc offers these or something similar. I will have to
check to see what it's called. They use the raw data from
a corneal topographer to manufacture the lenses.
hmmm, just checked his website. It's not on there any more.
Wonder if the company didn't make it or something? I'll
ask next time I go in.
-Quick |
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Dr Judy
medicine forum Guru
Joined: 07 May 2005
Posts: 304
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| Posted: Tue Jul 18, 2006 2:46 am Post subject:
Re: Contacts for astigmatism
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Charles wrote:
| Quote: | For astigmatism, especially if using RGP type lenses, it seems like you
could build the backside of the lens to fairly precisely match the
shape of the cornea. With it like this, the lens would suck in to the
cornea in a known orientation, so rotation would not be an issue
(assuming enough corneal astigmatism, and thin enough tear layer).
With that, the outer surface of the lens could be built to provide the
desired correction.
Why is this a bad idea? I assume someone has thought of it. Is it
just too hard to manufacture super custom lenses like that?
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Neither a bad idea nor a new one.
The lens you describe has been available as a rigid design for over 50
years, it is called a back toric and is used primarily to achieve a
better fit on corneas with significant astigmatism. The toric back
curve creates a tear lens with astigmatism which may or may not be
needed. If not needed then the front surface of the lens must also be
made toric to compensate. This is called a bitoric design.
It is more difficult to make and fit and is about double the cost of
spherical rigid lenses.
Quite a few of the soft toric lenses currently available use a toric
back surface as part of the stability design.
Dr Judy |
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Dr. Leukoma
medicine forum Guru
Joined: 30 Apr 2005
Posts: 1283
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| Posted: Wed Jul 19, 2006 11:00 am Post subject:
Re: Contacts for astigmatism
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Quick wrote:
| Quote: |
My doc offers these or something similar. I will have to
check to see what it's called. They use the raw data from
a corneal topographer to manufacture the lenses.
hmmm, just checked his website. It's not on there any more.
Wonder if the company didn't make it or something? I'll
ask next time I go in.
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Maybe they couldn't live up to their own hype. A common tale.
DrG |
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