Board index » lasik-eyes » This was asked before.

2004-04-11 12:10:19 PM
Someone was discussing this last month. It never really got
addressed.
Other than manufacturer and materials used and their intended use,
what is the difference in the shape of an RGP, Crystalens, reverse
geometry, ortho-k, and retainer lenes for myopia?
Don't they all involve a flattened central portion with some gaps at
the periphery to acoomodate the new shape of the cornea after the
central part is squashed flatter?
Are any of these lenses little more than rigid versions of a soft
contact that doesn't try to change the shape of the cornea itself?
Since rigid contacts probably give the best vision possible for people
who can tolderate them, and they are a viable alternative to LASIK, it
would be nice to know a little about them.
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On Sun, 11 Apr 2004 04:10:19 GMT, Ragnar Suomi <ragnarsuomi@yahoo.com>
wrote:
lens fitting.
vision, is well tolerated, and is acceptable to the patient is a
viable alternative to LASIK.
If you are asking if it is a long-term replacement for LASIK, that is
a different question and the answer would be more toward "not
necessarily". All reshaping of the cornea with contact lenses (only)
will regress when contact lens use is stopped. LASIK is a permanent
change.
Glenn Hagele
Executive Director
Council for Refractive Surgery Quality Assurance
Email to glenn dot hagele at usaeyes dot org
www.USAeyes.org
www.ComplicatedEyes.org
I am not a doctor.
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I thought up what might be the differences in these lenses.
An RGP lens inner surface fits the cornea whereas it's outer surface
is flatter. RGP lenses are probably the same as retainer lenses.
A reverse geometry lens which is similar to an ortho-k or a CRT lens
is a lens with a flat inner surface to force the cornea into a
flatter shape while the outer surface of the lens is "plano".
Did I get it right? I'm just guessing.
BTW, in the previous message I said Crystalens when I meant CRT lens.
A Crystalens is an accomodating IOL.
On Sun, 11 Apr 2004 04:10:19 GMT, Ragnar Suomi <ragnarsuomi@yahoo.com>
wrote:

lasik-eyes

Glenn - USAeyes.org <glenn.hageleSTOPSPAM@USAeyes.org>wrote in
published in the CLAO Journal, "Time to resolution of contact lens-induced
corneal warpage prior to refractive surgery," by Wang, McCulley, Bowman,
Cavanagh authors. They found that the average time to stability after
discontinuation of lens wear was 8.8 +/- 6.8 weeks for RGP lenses. In some
patients, warpage was 'resistant.' Soft extended wear patients showed the
greatest time to recovery, with an average of 11.6 weeks.
The question is whether one considers OK to be a form of controlled corneal
warpage, as I think it is. In which case, the effects of OK may not be
completely reversible in all cases, or may be highly resistant - as some
have suggested. This probably explains why there are anecdotal stories
about permanent refractive changes following OK.
I'm not certain that some of the companies promoting OK, like Paragon
Vision Sciences, want to promote the idea of permanent change. It seems
like they consider the reversible nature of OK as a key marketing feature.
DrG
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On Sun, 11 Apr 2004 17:43:48 GMT, "Dr. Leukoma" <drg@leukoma.com>
wrote:
11.6 weeks with extended wear soft contacts? Why would soft contacts
take longer? The soft contacts aren't even supposed to warp the
cornea.
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In article <Xns94C88248CC6FBDrLeukoma@207.217.125.206>,
"Dr. Leukoma" <drg@leukoma.com>wrote:
surgeons about how long to stay out of contact lenses before surgery is
too short. I think the general recommendation for soft lenses is
generally 3 days to 1 week. That's a lot less than 11.6 weeks.
--
"The truth lies somewhere between Ragnar and Flap Melt"
~RT
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Trent <ttmpa@aol.com>wrote in
tissue and has metabolic functions. It can swell under conditions of
hypoxia. You must remember that most of the extended wear soft lenses worn
for this study are of the older generation of hydrogel lenses. The cornea
swells an average of 9% with the best of these lenses at night. With the
newer generation of silicone-hydrogels, the corneal swelling is the same as
the baseline without lenses, i.e. about 4%. When the tissue swells, the
volume increases. Most people don't sleep in RGP lenses, which are
typically very oxygen permeable.
DrG
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RT <RTMD24nospam@yahoo.com>wrote in
average time to stability for daily wear soft lenses is much less.
The study concludes with the recommendation that the cornea be measured
repeatedly until there are no more changes. So, yes this probably does
have profound implications for how long is necessary for be out of one's
lenses before undergoing surgery.
DrG
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I thought I would recycle this message once more hoping for a
response.
On Sun, 11 Apr 2004 09:55:15 GMT, Ragnar Suomi <ragnarsuomi@yahoo.com>
wrote:
ortho-k is the thinning of the epithelium. The information said that
ortho-k's effects are more from a thinning of the central epithelium
than from the change in shape of the cornea. I'm uneasy about that
idea though. It seems to me that once the ortho-k lenses were taken
out, the epithelium would rapidly revert to it's original shape.
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Ragnar Suomi <ragnarsuomi@yahoo.com>wrote in
However, Helen Swarbrick also noted some changes in the anterior stroma.
In another post, I alluded to the possibility of irreversible changes.
Because of thinning central stroma, I am also uneasy about the overnight
use of OK lenses. More studies need to be done showing the integrity of
the epithelium in this area before I am comfortable. I am all for OK.
However, at this point I am reluctant to sell OK on the basis that it is
somehow safer or better than LASIK.
The answer to the question about the retainer lens for OK is that the CRT
lens becomes the retainer lens. In it's marketing presentations, Paragon
is promoting CRT on the basis of simplicity, i.e. one or two lenses to
achieve the final result - i.e. the same lens that molds the cornea keeps
it there.
DrG
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"Dr. Leukoma" <drgNOSPAM@leukoma.com>wrote in
actually thin in OK or CRT or whatever you wish to call it.
DrG
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"Dr. Leukoma" <drgNOSPAM@leukoma.com>schreef in bericht
Major snip......
uneasy.
The exchange of debri coming from the cornea is a hot issue to my opinion as
it is in soft night and day lenses.
More studies need to be done showing the integrity of
Jan (normally Dutch spoken)

"Dr. Leukoma" <drgNOSPAM@leukoma.com>wrote in message news:<Xns94C9476E61F1Edrgleukomacom@216.148.227.77>...
reversible procedure, to check if I can stick to it, before more
committed solutions like surgery on my corneas.
The optometrist took a topography on my eyes besides other more simple
tests. He assured me it is a reversible procedure(The ephiteleum is
the only layer affected).
If I don't like to do this every night or every other night, then I
consider Lasik. Also it will give me a notion of how important is for
me, not to use glasses.
It would be nice to know any good or bad, study or news about this,
but I believe there is a consensus that it is way less risk than
Lasik.
Let's see what happens.
Miguel
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I don't see why "reversible" is so great. I have no desire to revert
back to -7.75 with a load of astigmatism.
On Mon, 12 Apr 2004 22:00:00 +0200, "Jan"
<verwijderditoudes@haalditwegkabelfoon.nl>wrote:

On 12 Apr 2004 13:18:44 -0700, miguelyson@hotmail.com (Miguel) wrote:
the safest, most predictable surgery there is. One could debate
whether OK is "riskier" or not.
In your case, lets just say you want to try something else before
having LASIK. What have you got against wearing RGP lenses that are
not ortho-k lenses? Is there some reason you don't want lenses on
your eyes from the hours of 8am to 3pm?
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miguelyson@hotmail.com (Miguel) wrote in
I don't mean to discourage you from going the OK route, if you are a good
candidate. It is indeed a less invasive procedure than LASIK. Although
the rate of catastrophic complications involving a loss of vision is
extremely low, there have been a number of reports in the literature
involving overnight OK. OK has not been done in great numbers, and other
than the FDA there has been no central agency tracking the complications,
if they are reported. My only concern is that if overnight OK is performed
on large numbers of people, will this result in a "black-eye" on the
practice, similar to what happened with LASIK? Only time will tell.
Whether the epithelium is the only layer affected is still undecided, but
it is probably the principal layer involved in the refractive effect. In
the vast majority of cases, it is reversible, but in my experience can take
as long as a year to completely reverse.
I think you will be pleased with the results. Please keep us updated.
DrG
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outcome is a godsend.
Glenn Hagele
Executive Director
Council for Refractive Surgery Quality Assurance
Email to glenn dot hagele at usaeyes dot org
www.USAeyes.org
www.ComplicatedEyes.org
I am not a doctor.
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I do not believe Lasik is high risk and I did not said that. Is just
that Lasik is lot riskier than Corneal Refractive Therapy(CRT). Can
you understand this?
What am I going to do after 3PM (say 3-10PM), maybe I buy a dog to
guide me, drive me, tell me what the movies are about, HeHe.
Also there is a high chance of wearing the contact lenses every 2 or 3
nights after your vision is stable. So I am talking about a lot of
time without lenses in your eyes. Another answer is that in my house
I have control, when I sleep I don't care if I have or not contact
lenses. After 8AM I don't want foreign object inside my eyes. I would
prefer glasses. I know that at night no matter how good is the lens
is going to bother me. Also sports come into the equation,
etc,etc,etc.
Corneal Refractive therapy derives from ortho-k, but is not classic
ortho-k. Why? Because in ortho-k you use a series of lenses which mold
your cornea until you get to correct your refractive error. Then you
use a retainer lens that will maintain your vision nicely. In CRT you
use only one lens which gently molds your cornea and maintains it
after you have good vision. Also, I believe CRT is the only lens that
is approved by FDA to correct vision and that can be used while you
sleep. So CRT is less Contact lens fittings and simpler. I understand
CRT or Ortho-k have a more reduced market than refractive surgery.
This has been written after my first night using the lenses, but I
will comment about this later.
Miguel
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Good luck. I would suggest you wear RGPs during the day and forget
about ortho-K. If you can afford to experiment and are very patient,
then you might as well give ortho-k a shot. When people want
something to work, there is a much greater chance of it working.
On 15 Apr 2004 09:34:49 -0700, miguelyson@hotmail.com (Miguel) wrote:

miguelyson@hotmail.com (Miguel) wrote in
'orthos,' meaning straight or true, and 'keratology,' meaning the study of
or science of the cornea. The abbreviation CRT stands for Corneal
Refractive Therapy, and is a copyright of Paragon Vision Sciences, a
manufacturer of contact lenses. A more general description for CRT would
be overnight orthokeratology, which is more descriptive of the method,
without reference to a specific lens. Many companies have already entered
the field of overnight orthokeratology, and some are awaiting approval from
the FDA. The FDA can only approve a medical device, such as a contact lens
or a laser. It does not regulate the practice of medicine.
Overnight orthokeratology was being performed before the advent of CRT.
One of the ostensible reasons that the FDA became involved were the reports
of severe eye infections involving a few patients who were undergoing
overnight ortho-k. I believe that even though the CRT product has been
approved by the FDA, extensive post-marketing studies are still required.
The FDA is primarily concerned with two things: safety and efficacy. These
are relative, and not absolute terms.
DrG
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