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From: pwb@fritz.UUCP (Phil Bonesteele)
Newsgroups: net.med
Subject: Contact lenses and astigmatism...
Message-ID: <3420@fritz.UUCP>
Date: Wed, 31-Jul-85 12:44:19 EDT
Article-I.D.: fritz.3420
Posted: Wed Jul 31 12:44:19 1985
Date-Received: Sun, 4-Aug-85 04:54:00 EDT
Organization: FileNet Corp., Costa Mesa, Ca.
Lines: 47

Hello.  I hope to glean some information from informed persons on the
topic of contact lenses.  First, I have a mild astigmatism
(relatively  weak  in  the  left  eye).    I  can  see  20/20 without
correction, but still  have a problem making out  fine detail (print)
either  near  or  far,  which  causes  my  eyes to  tire quickly when
concentrating on things like CRTs, hardcopy, etc.  Thus after wearing
glasses the past seven years for reading, driving (to make out street
signs at a distance), etc., I've decided to get contact  lenses.  The
two  main  reasons  for  getting contacts  now are  that I  am not as
diligent as  I should  be about  wearing my  glasses (so  my eyes get
quite sore after a few rounds  at the  terminal), and  I've picked up
flying again after a LONG  absence and  need to  be able  to pick out
other aircraft  at a  distance, which  means I  need to  wear BOTH my
correction and good sunglasses.  

I recently had a eye examination for  the fitting  of contact lenses.
This  is  the  information  I  received  from  the  optometrist:  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.  Apparently the common astigmatism is a condition where
the cornea has the correct curvature in one  axis and  not the other.
Soft lenses can correct for this by adhering to the  cornea, with the
lens  thickness  varying  the  correct  amount to  compensate for the
inaccurate curvature along the one axis.   This requires  the lens be
oriented correctly on the cornea.  All  contact lenses,  hard or soft
`float' around when you blink, such  that soft  lenses correcting for
an astigmatism must realign themselves whenever `floating' mismatches
the thickness of the lens  with the  cornea.   Apparently hard lenses
can correct for an  astigmatism by  becoming the  new corneal surface
with the correct curvature in both axis.   The hard  lens will adhere
to the axis of the  cornea with  the correct  curvature, but separate
from the incorrect curvature axis.   This  space is  filled with tear
solution such that the  combination of  hard lens,  tear, and natural
cornea  together  form  a  `new'  cornea  with  the  correct  optical
properties and curvatures in both axis.   Thus any  `floating' of the
hard lenses won't  greatly affect  vision quality, unlike soft lenses
(that correct for astigmatism).  

I would appreciate if any informed netters out there could tell me if
the  above information is  pretty much correct, or if the optometrist
was just passing gas.  Thanks in advance.

		Phil Bonesteele
		FileNet Corp.
		Costa Mesa, CA
		{decvax, ucbvax, ihnp4, hplabs}!trwrb!felix!pwb