pwb@fritz.UUCP (Phil Bonesteele) (07/31/85)
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!pwbdebbiem@rruxe.UUCP (D. McBurnett) (08/05/85)
Phil, As I have had it from several opthmologists (sp?) and optometrists, the explanation you got is essentially correct. I have a BAD astigmatism in one eye, and am therefore doomed to wearing hard lenses (I've been told that there is a CHANCE I could wear gas- permeable lenses, but since the experiment would cost me over $250, I'm not willing to find out). But since glasses don't correct my astigmatism completely, and in any case cost more than the hard lenses, I'm willing to put up with the less-than-ideal comfort of hard lenses. P.S. One virtue of hard lenses is that when they get scratched up, you can get them polished again for about $10 and they are as good as new again. I don't think this can be done with any other kind of contact lens. The pair I'm wearing now are four years old and going strong -- so far they have cost me all of $45. And when they are newly polished, they are quite comfortable. Debbie McBurnett rruxe!debbiem
brian@leadsv.UUCP (Brian Atwood) (08/05/85)
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. > Phil Bonesteele > FileNet Corp. > Costa Mesa, CA > {decvax, ucbvax, ihnp4, hplabs}!trwrb!felix!pwb 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. Brian Atwood LMSC
dr@ski.UUCP (David Robins) (08/06/85)
> Hello. I hope to glean some information from informed persons on the > topic of contact lenses. First, I have a mild astigmatism --------------> > 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. The optometrist gave you a very thorough explanation, and your understanding of it is correct. Soft contact lenses for astigmatism do need to stay oriented to the corneal axes in order to compensate for the astigmatism. This is accomplished by either ballast weighting (thickening) the bottom of the lens, so gravity pulls this edge down, or by truncating the edge, so contact with the lower lid keeps it in position. Trouble is, at each blink, the lids move sideways slightly, thereby torting the lens. After the blink, the lens realigns itself, but this takes a short time (less than 1 second, usually). However, if there is a significant astigmatism, or if one is acutely aware of one's vision, the time when the lens is not aligned may cause blurred vision, and can thus be annoying. These problems are largely eliminated by rigid contact lenses. Hard contact lenses (non-permeable) and gas-permeable contact lenses are spherical on the front and back surfaces. As long as there is not too much astigmatism (less than about 2.50 or 3.00 diopters of keratometer- reading curvature), the spherical surface sits on the toric surface of the astigmatic cornea reasonably well, thereby forming a new, spherical front optical surface. This eliminates the optical aberrations. In high astigmatism cases, the posterior curve of the contact lens can be made toric, instead of spherical, to get a better fit. However, then the anterior surface must be toric also. Manufacturing such lenses is an art, and fitting them is not easy. Gas-permeable CL's are not as rigid as hard CL's, and they can bend a bit if there is much corneal toricity. However, on the whole, gas-permable CL's are healthier for the cornea. Hard CL's, with no oxygen transmission, have sometimes caused permanent corneal warping. Any rigid CL will put pressure on the toric cornea, causing a temporary curvature change. This may be noticeable after taking the lenses off and putting on one's glasses. The usual CL should not take more than about 1/2 hour to bounce back. Corneal moulding takes longer to undo, even up to several weeks in severe cases. -- ==================================================================== David Robins, M.D. Smith-Kettlewell Institute of Visual Sciences 2232 Webster St; San Francisco CA 94115 415/561-1705 {ihnp4,qantel,dual}!ptsfa!ski!dr
dr@ski.UUCP (David Robins) (08/09/85)
> 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 {ihnp4,qantel,dual}!ptsfa!ski!dr