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From: dr@ski.UUCP (David Robins)
Newsgroups: net.med
Subject: Re: Contact lenses and astigmatism...
Message-ID: <193@ski.UUCP>
Date: Thu, 8-Aug-85 19:51:15 EDT
Article-I.D.: ski.193
Posted: Thu Aug  8 19:51:15 1985
Date-Received: Mon, 12-Aug-85 05:31:15 EDT
References: <3420@fritz.UUCP> <549@leadsv.UUCP>
Organization: Smith-Kettlewell Institute, S.F., CA.
Lines: 42

> In article <3420@fritz.UUCP>, pwb@fritz.UUCP (Phil Bonesteele) writes:
> > Hello.  I hope to glean some information from informed persons on the
> > topic of contact lenses. 
> > The optometrist's opinion was that for my weak  prescription, soft lenses
> > wouldn't improve my  vision all  that much.   But  that gas permeable
> > hard lenses would correct my mild astigmatism and still leave me with
> > clear vision. 
-------------------
> I too have an astigmatism. A few years ago I got a pair of gas permeable hard
> contact lenses and from what my optometrist told me, they have reshaped my 
> cornea. In normal wear they make the cornea conform to the lens and this
> apparently permanently reshaped the lens. I don't know if an astigmatism
> can be "cured" by this method, though.

All rigid contact lenses "mould" the cornea through normal wear.  If
two surfaces meet, and one is softer (ie, the cornea), it "gives" and
conforms to the spherical back surface of the contact lens.  Howver,
since gas-permable lenses are somewhat flexible, due to the plastics
used, theis lens can warp; if it doesn't, the moulding occurs.

Also, the degree of moulding is influenced by the lack of oxygen
beneath the lens; thus, gas-permable lenses *may* cause less of this
effect.  In additon, the degree of moulding is influnced by one's own
genetic makeup....some people have a tendency to warp, perhaps
permanently.  Some cases of acquired keratoconus, which is seen in
non-contact lens wearers also, may occur at higher incidence with
rigid contact lenes, especially if fitted too tightly.

In the the second letter, above, there is an error.  The contact len
reshapes the cornea, not the lens (of the eye).  Hopefully the
reshaping is not permanent, which indicates something bad is
happening.  The usual moulding springs back in a few hours to a few
weeks.  (It is this prolonged effect that is aimed for by
orthokeratologists; contact lens fitters who are TRYING to flatten or
mould the cornea for a temporary better acuity.)
-- 
====================================================================
David Robins, M.D. 
Smith-Kettlewell Institute of Visual Sciences
2232 Webster St; San Francisco CA 94115
415/561-1705
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