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Home > Archive > Lasik Eyes Surgery > March 2005 > Correction of astigmatism only?
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Correction of astigmatism only?
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| Graeme Hewson 2005-03-19, 6:24 pm |
| I've been wondering if it's possible to correct astigmatism with RS
while undercorrecting myopia. My prescription is roughly -3D, with
another -3D of astigmatism, and (I'm 50) I find I spend most of my time
wearing glasses with a +1.25D addition. They're good for looking at a
computer monitor and normal-size print and good enough for gazing out of
the window and getting around, but not great for watching TV; I don't
spend so long in the week watching TV, though, or driving.
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| Glenn - USAEyes.org 2005-03-19, 6:24 pm |
| Proceed very, very carefully with this idea.
Most current laser systems automatically correct myopia (nearsighted,
shortsighted) when correcting astigmatism. The ratio is about 0.25
diopter myopia for every 1.00 diopter astigmatism. That means that
you could end up being 0.75 D hyperopic (farsighted, longsighted)
after surgery.
Yes, the doctor could then do a hyperopic correction, but that is a
lot of manipulation of the cornea and this kind of manipulation is an
opportunity for degradation in your vision. You are NOT the "perfect
LASIK candidate" and refractive surgery may not be wise at all.
Using the +1.25 addition reading glasses indicates that you are over
age 40 and are presbyopic. That is when the natural lens of the eye
is no longer able to change focus from distant to near. The
combination of hyperopia and presbyopia often means poor quality
vision at all distances.
I recommend that you work with a good optometrist for a toric contact
lens fitting before considering refractive surgery. If you decide to
investigate further, be sure to grill your doctor on exactly how his
or her system will not make you hyperopic.
Glenn Hagele
Executive Director
Council for Refractive Surgery Quality Assurance
Email to glenn dot hagele at usaeyes dot org
http://www.USAEyes.org
http://www.ComplicatedEyes.org
I am not a doctor.
| |
| Graeme Hewson 2005-03-19, 6:24 pm |
| On Sat, 19 Mar 2005 08:13:52 GMT, glenn.hageleSTOPSPAM@USAEyes.org
(Glenn - USAEyes.org) wrote:
> Proceed very, very carefully with this idea.
Indeed.
> Most current laser systems automatically correct myopia (nearsighted,
*automatically*? Isn't the surgeon in control?
> Using the +1.25 addition reading glasses indicates that you are over
> age 40
Yes, 50, as I said (albeit parenthetically.)
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| Glenn - USAEyes.org 2005-03-19, 6:24 pm |
| Although many may think they can, physicians do not control the laws
of physics. Due to the methodology used to treat astigmatism with
excimer laser, the physics dictate a myopic correction to astigmatic
correction ratio of .25 to 1.00.
Glenn
Glenn Hagele
Executive Director
Council for Refractive Surgery Quality Assurance
Email to glenn dot hagele at usaeyes dot org
http://www.USAEyes.org
http://www.ComplicatedEyes.org
I am not a doctor.
| |
| Graeme Hewson 2005-03-19, 6:24 pm |
| So if the surgeon corrects for astigmatism, the correction for myopia
follows according to the laws of physics, and vice versa?
How do you mean by "*most* current laser systems"?
| |
| Ragnar 2005-03-19, 6:24 pm |
| You might want to check those astigmatism numbers again. That sounds
like the limited correction of the NIDEK system, not the VISX system.
On Sat, 19 Mar 2005 15:58:36 GMT, Glenn - USAEyes.org
<glenn.hageleSTOPSPAM@USAEyes.org> wrote:
>Although many may think they can, physicians do not control the laws
>of physics. Due to the methodology used to treat astigmatism with
>excimer laser, the physics dictate a myopic correction to astigmatic
>correction ratio of .25 to 1.00.
>
>Glenn
>
>Glenn Hagele
>Executive Director
>Council for Refractive Surgery Quality Assurance
>
>Email to glenn dot hagele at usaeyes dot org
>
>http://www.USAEyes.org
>http://www.ComplicatedEyes.org
>
>I am not a doctor.
| |
| Glenn - USAEyes.org 2005-03-19, 6:24 pm |
| It is my understanding that at least one of the laser systems uses a
different methodology for the correction of astigmatism that is not
plagued by the myopia to astigmatism ratio. I intend to research this
further at a medical conference coming up next month and I should be
much more knowledgeable about how to get around the problem.
Before you ask, the problem exists with both conventional and
wavefront-guided ablations.
Glenn Hagele
Executive Director
Council for Refractive Surgery Quality Assurance
Email to glenn dot hagele at usaeyes dot org
http://www.USAEyes.org
http://www.ComplicatedEyes.org
I am not a doctor.
| |
| Glenn - USAEyes.org 2005-03-19, 6:24 pm |
| >You might want to check those astigmatism numbers again. That sounds
>like the limited correction of the NIDEK system, not the VISX system.
When I last checked, it applied to all but (my memory here) the
Allegretto. I know for a fact that the VISX has this limitation, as
well as other peculiarities with astigmatic correction. I will be
attending the ASCRS convention and will do the additional research on
this.
Glenn Hagele
Executive Director
Council for Refractive Surgery Quality Assurance
Email to glenn dot hagele at usaeyes dot org
http://www.USAEyes.org
http://www.ComplicatedEyes.org
I am not a doctor.
| |
| CatmanX 2005-03-19, 6:24 pm |
| Glenn, last I checked, -3.00/-3.00 would be easy enough, given that
there would be -0.75 correction of myopia, thus the myopic component
would be calculated at -1.50 to -2.25 depending on whether you wanted
to leave a little residual myopia.
grant
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| Glenn - USAEyes.org 2005-03-23, 5:43 pm |
| I need to do something about my reading comprehension. I did not
catch the 3.00 D myopia. Yes, in this case being overcorrected into
hyperopia is not as much of a concern. Whenever astigmatism is
greater than one-half the myopia the success rates go down, but that
is a very different situation than what I was initially describing.
Thanks doc.
Glenn Hagele
Executive Director
Council for Refractive Surgery Quality Assurance
Email to glenn dot hagele at usaeyes dot org
http://www.USAEyes.org
http://www.ComplicatedEyes.org
I am not a doctor.
| |
|
| I am also considering surgery (advanced surface ablation) and I have
astigmatism or 2.5 and nearsighted by 1.25 and 1.5. The doctor said I was
an excellent candidate. Reading this tells me I might not be. I don't
really understand the technical jargon, but would like to know if the
surgeon is BSing me.
"Glenn - USAEyes.org" <glenn.hageleSTOPSPAM@USAEyes.org> wrote in message
news:m2ar31phdpqctkdet3p5mq1iim5mhgveh0@4ax.com...
>I need to do something about my reading comprehension. I did not
> catch the 3.00 D myopia. Yes, in this case being overcorrected into
> hyperopia is not as much of a concern. Whenever astigmatism is
> greater than one-half the myopia the success rates go down, but that
> is a very different situation than what I was initially describing.
>
> Thanks doc.
>
> Glenn Hagele
> Executive Director
> Council for Refractive Surgery Quality Assurance
>
> Email to glenn dot hagele at usaeyes dot org
>
> http://www.USAEyes.org
> http://www.ComplicatedEyes.org
>
> I am not a doctor.
| |
| Glenn - USAEyes.org 2005-03-23, 5:44 pm |
| In my opinion, you are not an ideal candidate, but may be an
appropriate candidate when all other issues are considered.
Astigmatism means that your cornea is not spherical like the top of a
ball, but elliptical like the back of a spoon. Astigmatism is
primarily a problem of topography. To oversimplify; your cornea has a
"bump" out at its edge.
Myopia (nearsighted, shortsighted) means that when relaxed your eye
focuses objects in front of the back of the eye. By bending light
with contacts or glasses, the focus point can be moved back to the
retina where it is needed for best vision.
Refractive surgery like LASIK attempts to change this focus point by
changing the shape of the cornea. For the vast majority of patients
this works fine and they have a reduced need for corrective lenses.
Because it works well for some does not mean that it will work well
for all.
In my opinion, anyone who has astigmatism that is more than half of
their myopia is not an ideal candidate. That does not mean that they
will necessarily get a bad result, nor does it mean they will not have
a reduced need for glasses or contacts. It simply means that the
probability of the sought perfect uncorrected vision is significantly
reduced.
Others will argue with this opinion and can offer up many patients
with astigmatism higher than myopia who got good results. Sure, it
can happen, but it will happen less often than with someone who has
minor or nor astigmatism.
So, you may be appropriate depending upon all factors combined (like a
very small pupil), but IMO you are not an ideal candidate. Of course,
I tend to be a bit more conservative than many doctors.
Glenn Hagele
Executive Director
Council for Refractive Surgery Quality Assurance
Email to glenn dot hagele at usaeyes dot org
http://www.USAEyes.org
http://www.ComplicatedEyes.org
I am not a doctor.
| |
|
| OK, I am not quite understanding the whole astigmatism problem. The doctor
told me that he would only be removing about 15% of my cornea. I just
assumed that if he made the cornea the right shape I would have good vision.
I am starting to think it is allot more complicated than that. If the
cornea is the ideal shape, why would I not have good vision? What is the
difference of removing astigmatism vs. removing nearsightedness or
farsightedness?
I am thinking about having the Ladarvision 4000 advanced surface ablation.
Is there a better laser/technique for me? If I do this what should I
realistically expect for results. I am fairly young healthy person.
"Glenn - USAEyes.org" <glenn.hageleSTOPSPAM@USAEyes.org> wrote in message
news:81q1415utkt0ku6vtas76scqllk52andb2@4ax.com...
> In my opinion, you are not an ideal candidate, but may be an
> appropriate candidate when all other issues are considered.
>
> Astigmatism means that your cornea is not spherical like the top of a
> ball, but elliptical like the back of a spoon. Astigmatism is
> primarily a problem of topography. To oversimplify; your cornea has a
> "bump" out at its edge.
>
> Myopia (nearsighted, shortsighted) means that when relaxed your eye
> focuses objects in front of the back of the eye. By bending light
> with contacts or glasses, the focus point can be moved back to the
> retina where it is needed for best vision.
>
> Refractive surgery like LASIK attempts to change this focus point by
> changing the shape of the cornea. For the vast majority of patients
> this works fine and they have a reduced need for corrective lenses.
> Because it works well for some does not mean that it will work well
> for all.
>
> In my opinion, anyone who has astigmatism that is more than half of
> their myopia is not an ideal candidate. That does not mean that they
> will necessarily get a bad result, nor does it mean they will not have
> a reduced need for glasses or contacts. It simply means that the
> probability of the sought perfect uncorrected vision is significantly
> reduced.
>
> Others will argue with this opinion and can offer up many patients
> with astigmatism higher than myopia who got good results. Sure, it
> can happen, but it will happen less often than with someone who has
> minor or nor astigmatism.
>
> So, you may be appropriate depending upon all factors combined (like a
> very small pupil), but IMO you are not an ideal candidate. Of course,
> I tend to be a bit more conservative than many doctors.
>
> Glenn Hagele
> Executive Director
> Council for Refractive Surgery Quality Assurance
>
> Email to glenn dot hagele at usaeyes dot org
>
> http://www.USAEyes.org
> http://www.ComplicatedEyes.org
>
> I am not a doctor.
| |
| Glenn - USAEyes.org 2005-03-24, 12:29 pm |
| Correcting myopia is simply flattening the cornea evenly across the
centermost portion and transitioning out to the outer edges of the
treatment zone.
Correcting astigmatism is applying more laser energy (and tissue
removal) to effect a greater flattening of the meridian where the "tip
of the spoon" is pointed.
A limitation of all refractive surgery is that corneas are biological
material, not something nice and predictable like plastic. Sometimes
the eye just doesn't do what is expected. This unexpected outcome
tends to happen more often with astigmatic correction and
significantly more often with high astigmatic correction.
My personal opinion is that the LADARVision 4000 CustomCornea is a
fine excimer laser, but there are those who argue otherwise. I
recommend you do a search in this newsgroup on the words "Alcon" and
"LADARVision" and look at the postings from Rebecca and me.
Yes, LASIK is very complicated. You are talking about microsurgery on
your eye that changes the way light bends and the frequency at which
light hits the retina and is "seen".
Glenn Hagele
Executive Director
Council for Refractive Surgery Quality Assurance
Email to glenn dot hagele at usaeyes dot org
http://www.USAEyes.org
http://www.ComplicatedEyes.org
I am not a doctor.
| |
|
| That makes sense to me. The place I am going to says they offer free
enhancements if needed. Would an enhancement fix the not perfect (20/20)
vision if I did not achieve it? The doctor told me he would remove only 15%
of the cornea. Is that allot? An enhancement would take even more. How
much is too much?
> Correcting myopia is simply flattening the cornea evenly across the
> centermost portion and transitioning out to the outer edges of the
> treatment zone.
>
> Correcting astigmatism is applying more laser energy (and tissue
> removal) to effect a greater flattening of the meridian where the "tip
> of the spoon" is pointed.
>
> A limitation of all refractive surgery is that corneas are biological
> material, not something nice and predictable like plastic. Sometimes
> the eye just doesn't do what is expected. This unexpected outcome
> tends to happen more often with astigmatic correction and
> significantly more often with high astigmatic correction.
>
> My personal opinion is that the LADARVision 4000 CustomCornea is a
> fine excimer laser, but there are those who argue otherwise. I
> recommend you do a search in this newsgroup on the words "Alcon" and
> "LADARVision" and look at the postings from Rebecca and me.
>
> Yes, LASIK is very complicated. You are talking about microsurgery on
> your eye that changes the way light bends and the frequency at which
> light hits the retina and is "seen".
>
> Glenn Hagele
> Executive Director
> Council for Refractive Surgery Quality Assurance
>
> Email to glenn dot hagele at usaeyes dot org
>
> http://www.USAEyes.org
> http://www.ComplicatedEyes.org
>
> I am not a doctor.
| |
| Glenn - USAEyes.org 2005-03-24, 12:29 pm |
| Depending upon the situation, an enhancement may work or may make the
situation worse.
Remember when I talked earlier about the automatic myopic correction
with astigmatic correction? For every 1.00 diopter of astigmatic
correction, most current systems automatically also correct 0.25 D of
myopia whether you need it or not.
If your initial surgery corrects all the myopia but not all the
astigmatism, then an enhancement for the astigmatism could cause you
to become hyperopic (farsighted). That is not something you want.
Yea, I know. Then you could have hyperopic surgery to correct the
hyperopia. That much and that kind of corneal manipulation simply is
not wise and should be avoided. It is like the gambler saying that he
hopes he breaks even tonight because he needs the money. If you are
going to go through all this with all that potential for risk, you are
better off doing nothing.
Talking about removing a percentage of the cornea is getting into the
minute details that relate to how the curvature of the cornea will
change and how that may affect night vision problems due to induced
spherical aberration. To be honest, I'll bet the doctor was not
talking to you (a potential patient) about such nuances. The doctor
was probably just mentioning a fact that may make you feel more
comfortable with the surgery.
What is very important is the amount of cornea that remains
untouched. A healthy eye needs at least 250 microns of untouched
tissue to remain stable. Visit
http://www.usaeyes.org/faq/subjects..._pupil_size.htm where this
issue is discussed with detail.
I cannot tell you if 15% is going to be a real issue without knowing
such details as your current corneal curvature (K reading), the size
of the treatment zone, the size of the transition zone, the projected
ablation depth, the projected depth of LASIK flap (if LASIK is
considered), the current thickness of the cornea at the location most
thin, the size of your scotopic pupils, and a few other points. In
other words, we are getting to where I'm playing doctor and you need
to rely on a real doctor to give you these answers.
Glenn Hagele
Executive Director
Council for Refractive Surgery Quality Assurance
Email to glenn dot hagele at usaeyes dot org
http://www.USAEyes.org
http://www.ComplicatedEyes.org
I am not a doctor.
| |
|
| What do you guys think of this. http://www.drbrems.com/Bremsmarker.html
> Depending upon the situation, an enhancement may work or may make the
> situation worse.
>
> Remember when I talked earlier about the automatic myopic correction
> with astigmatic correction? For every 1.00 diopter of astigmatic
> correction, most current systems automatically also correct 0.25 D of
> myopia whether you need it or not.
>
> If your initial surgery corrects all the myopia but not all the
> astigmatism, then an enhancement for the astigmatism could cause you
> to become hyperopic (farsighted). That is not something you want.
>
> Yea, I know. Then you could have hyperopic surgery to correct the
> hyperopia. That much and that kind of corneal manipulation simply is
> not wise and should be avoided. It is like the gambler saying that he
> hopes he breaks even tonight because he needs the money. If you are
> going to go through all this with all that potential for risk, you are
> better off doing nothing.
>
> Talking about removing a percentage of the cornea is getting into the
> minute details that relate to how the curvature of the cornea will
> change and how that may affect night vision problems due to induced
> spherical aberration. To be honest, I'll bet the doctor was not
> talking to you (a potential patient) about such nuances. The doctor
> was probably just mentioning a fact that may make you feel more
> comfortable with the surgery.
>
> What is very important is the amount of cornea that remains
> untouched. A healthy eye needs at least 250 microns of untouched
> tissue to remain stable. Visit
> http://www.usaeyes.org/faq/subjects..._pupil_size.htm where this
> issue is discussed with detail.
>
> I cannot tell you if 15% is going to be a real issue without knowing
> such details as your current corneal curvature (K reading), the size
> of the treatment zone, the size of the transition zone, the projected
> ablation depth, the projected depth of LASIK flap (if LASIK is
> considered), the current thickness of the cornea at the location most
> thin, the size of your scotopic pupils, and a few other points. In
> other words, we are getting to where I'm playing doctor and you need
> to rely on a real doctor to give you these answers.
>
> Glenn Hagele
> Executive Director
> Council for Refractive Surgery Quality Assurance
>
> Email to glenn dot hagele at usaeyes dot org
>
> http://www.USAEyes.org
> http://www.ComplicatedEyes.org
>
> I am not a doctor.
| |
| Glenn - USAEyes.org 2005-03-29, 7:24 pm |
| It is a device to mark the cornea so the cyclorotation that occurs
when you move from standing or sitting to laying down does not create
an inaccurate treatment axis. Many doctors use this or similar kinds
of devices.
Glenn Hagele
Executive Director
Council for Refractive Surgery Quality Assurance
Email to glenn dot hagele at usaeyes dot org
http://www.USAEyes.org
http://www.ComplicatedEyes.org
I am not a doctor.
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