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Home > Archive > Lasik Eyes Surgery > March 2005 > P-IOL Preop Measurements Inadequate
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P-IOL Preop Measurements Inadequate
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| Glenn - USAEyes.org 2005-03-19, 6:22 pm |
| One of the major concerns we have expressed with the Phakic Intraocular
Lens (P-IOL) is that the current measurement techniques to determine
proper fitting are wholely inadequate. This recent article agrees:
"White-to-white measurement no longer sufficient for sizing IOLs
ROME - Measurement of the white-to-white distance can no longer be
accepted as a sufficient method for sizing posterior or anterior
chamber IOLs, according to Philippe Sourdille, MD."
http://www.osnsupersite.com/default.asp?ID=9850
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| Glenn,
A small point here. You said, "...the current measurement techniques to
determine proper fitting [of IOLs] are wholely inadequate." The
implication of your post is that ALL IOL measurement techinques are
inadequate. (That's how I took your post.)
What the doctor in the referenced article actually says is that
"white-to-white" distance should no longer be accepted as a method for
sizing IOLs. He says, "...we currently have the sophisticated, high
precision technology for measuring scientifically both the anterior and
posterior chamber, and sizing the IOLs accordingly..." He goes on to
say, "there are evaluation centers in universities and large private
practices where patients can receive all the necessary preoperative
tests".
So, not all techniques for determining the proper fitting of IOLs are
inadequate.
R
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| Glenn - USAEyes.org 2005-03-19, 6:22 pm |
| Thanks for the clarification and expansion. You are absolutely
correct.
Yes, using ultrasound immersion technology (Artemis) to measure for
IOLs (especially P-IOLs) is excellent, very accurate, and is the
direction I hope the industry goes, however that is not the current
norm. In fact, I believe there are less than two dozen of these
devices in the entire US.
The vast majority of patients are measured with white-to-white and this
is the technique submitted to the FDA for its approval consideration of
the STAAR ICL P-IOL. White-to-white is what the manufacturers of STAAR
say is the recommended protocol.
The issue is especially critical for the STAAR ICL because it needs to
sit in a ridge in the ciliary sulcus that may not even exist and cannot
be seen by conventional methods. The immersion ultrasound can
determine not only the appropriate size measurement, but can show if
this necessary component is intact on the patient and the STAAR ICL is
an appropriate choice.
If I had my way (and I seldom do), Artemis or similar evaluation would
be standard of care.
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| Well, if someone were looking for an IOL, it is good to know the best
method of getting an accurate measurement. If I were, I'd be looking
for one of those locations where ultrasound immersion is being
performed. Thanks for posting the article.
On a similar bent toward lasik standards - What would you consider to
be the "ultrasound immersion" (best way) method for measuring pupil
size and corneal thickness as part of a lasik evaluation? And what are
the methods for measuring these that were the part of the FDA approval
of lasik? (I understand there were different approvals of specific
lasers, etc. I'm just looking for a generalization. Using the IOL
example as a pattern.)
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| Glenn - USAEyes.org 2005-03-19, 6:22 pm |
| What is most important is that the pupil is measured and measured
accurately in both low light and ordinary light conditions. This then
needs to be considered when planning the size of the optical ablation
zone while taking into account other issues, such as percentage of
tissue removal, amount of refractive change, corneal curvature, age of
patient, etc. See
http://www.usaeyes.org/faq/subjects..._pupil_size.htm for details.
I am partial to the Procyon pupillometer. The Procyon provides an
objective method for measuring pupil size at controlled light levels
with a permanent printed record. The infared Colvard is the one most
doctors I know use. Colvard measures the pupil in zero light, so it
tends to over estimate the low light pupil size by about 1.0mm. A
simple ruler is surprisingly accurate in the hands of someone who knows
what he or she is doing. I know a few doctors who can simply look at a
patient's eyes and tell you within 0.5mm their pupil size, although I
would not want to rely on that particular standard.
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| Thanks for the info on pupil measurement. What instrument(s) would you
prefer for measuring corneal thickness?
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| rebeccaNO_SPAM@lasermyeye.org 2005-03-19, 6:22 pm |
|
r wrote:
> On a similar bent toward lasik standards - What would you consider to
> be the "ultrasound immersion" (best way) method for measuring pupil
> size
R,
There is a lot of mythology propagated about pupil size measurements,
scotopic, mesopic, which tool is best, etc. The main issue with pupil
measurements is in fact following proper scientific protocols to
dark-adapt the pupil - and it is here that pupil measurements so
frequently break down. Patients are measured while sitting in a lit
hallway, measured in a dark room right AFTER the door is opened to
admit the doctor, etc etc.
For more information about dark-adaptation, suggest you read: Accurate
pupil measurement in laser vision correction, at
http://www.lasermyeye.org/keratosco...g11jun2003.html
Rebecca Petris
www.lasermyeye.org
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| In perusing the official transcript of the FDA Ophthalmic Device Panel
regarding the IOL last February 5, 2004, there can be found NOT EVEN
ONE, SINGLE reference to white-to-white measurement in your
presentation, although it was discussed by another individual
presenting before the same panel.
Why, if this is such a major concern to you, did you fail to bring it
to the panel's attention while the devices were up for approval? You
presentation made numerous references to Lasik, the business your trade
organization markets, but which were totally irrelevant to the IOL
discussion taking place.
WHY DID YOU SAY NOTHING WHEN YOU HAD THE PENULTIMATE OPPORTUNITY?
Your slip is showing, Glenn.
Read the transcript here:
http://www.fda.gov/ohrms/dockets/ac...ipts/4023t1.htm
................................................................................................
CRSQA represents CRSQA surgeons and Glenn Hagele. Period.
................................................................................................
Glenn - USAEyes.org wrote:
> One of the major concerns we have expressed with the Phakic
Intraocular
> Lens (P-IOL) is that the current measurement techniques to determine
> proper fitting are wholely inadequate. This recent article agrees:
>
> "White-to-white measurement no longer sufficient for sizing IOLs
> ROME - Measurement of the white-to-white distance can no longer be
> accepted as a sufficient method for sizing posterior or anterior
> chamber IOLs, according to Philippe Sourdille, MD."
>
> http://www.osnsupersite.com/default.asp?ID=9850
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| Rebecca,
Thanks for the information. I do understand that the best tool used
incorrectly, will yield bad results. I've visited your site on many
occasions, and those "Lone Dog" articles are very informative. I
understand and appreciate your fundamental objections to lasik, but
what would your preferred method for measuring pupil size be?
R
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| Glenn - USAEyes.org 2005-03-19, 6:22 pm |
| There is no mention of white-to-white measurement in my presentation to
the FDA Opththalmic Devices Panel regarding the Artisan/Verisyse phakic
intraocular lens (P-IOL) because measurements of this sort are not
utilized with this type of P-IOL. While others may attempt to use any
opportunity in front of the ODP to raise any concern about any
ophthalmic product, I keep my comments relative to the actual device
being considered by the panel.
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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| Glenn - USAEyes.org 2005-03-19, 6:22 pm |
| There are several excellent methods. I believe that orbscan
preoperatively is probably most ideal because it provides not only
thickness at many different reference points throughout the cornea, but
also additional diagnostic information of great importance.
Intraoperatively, a touch pen style device is probably best to measure
the actual thickness at the interface to be certain that the LASIK flap
is not too thick and the residual bed would be too thin.
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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| You're spinning again, Glenn.
.............................................................
....................................
CRSQA represents CRSQA surgeons and Glenn Hagele. Period.
.............................................................
....................................
Glenn - USAEyes.org wrote:
> There is no mention of white-to-white measurement in my presentation
to
> the FDA Opththalmic Devices Panel regarding the Artisan/Verisyse
phakic
> intraocular lens (P-IOL) because measurements of this sort are not
> utilized with this type of P-IOL. While others may attempt to use
any
> opportunity in front of the ODP to raise any concern about any
> ophthalmic product, I keep my comments relative to the actual device
> being considered by the panel.
>
> 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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| Richard 2005-03-19, 6:22 pm |
| "Glenn - USAEyes.org" <glenn.hagele@usaeyes.org> wrote in
news:1107926037.539598.19560@f14g2000cwb.googlegroups.com:
> What is most important is that the pupil is measured and measured
> accurately in both low light and ordinary light conditions. This then
> needs to be considered when planning the size of the optical ablation
> zone while taking into account other issues, such as percentage of
> tissue removal, amount of refractive change, corneal curvature, age of
> patient, etc. See
> http://www.usaeyes.org/faq/subjects..._pupil_size.htm for details.
>
> I am partial to the Procyon pupillometer. The Procyon provides an
> objective method for measuring pupil size at controlled light levels
> with a permanent printed record. The infared Colvard is the one most
> doctors I know use. Colvard measures the pupil in zero light, so it
> tends to over estimate the low light pupil size by about 1.0mm.
Pupils do not adapt with zero light, they will remain at whatever size they
were at prior to the zero light condition, barring the use of drugs to
dilate them. I have to assume that the Colvard measures in very low light
conditions rather than zero, otherwise, it's accuracy would be way off,
again, barring the use of drugs to dilate the pupils.
--
Richard
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| rebeccaNO_SPAM@lasermyeye.org 2005-03-19, 6:22 pm |
|
r wrote:
> Thanks for the information. I do understand that the best tool used
> incorrectly, will yield bad results. I've visited your site on many
> occasions, and those "Lone Dog" articles are very informative. I
> understand and appreciate your fundamental objections to lasik,
Hmmmm. I am not aware I have ever voiced a "fundamental objection to
lasik". My objections are to poor medical practice, particularly in
terms of patient selection, counselling and informed consent. Our About
page sets out our goals for the industry pretty clearly in this regard
and others:
http://www.lasermyeye.org/about/index.html
> what would your preferred method for measuring pupil size be?
Hate to sound like a broken record, but I truly do believe that the
tool becomes irrelevant if scientifically-based dark-adaptation
protocols are not followed. Remember, there's no danger whatsoever of
over-measurement - the danger to the patient is exclusively that the
dark-adapted pupil could be undermeasured (and therefore either a
smaller POZ than appropriate and/or inappropriate patient counseling
and informed consent). I have seen what I think to be accurate and
inaccurate measurements on both Colvard and Procyon. None of the
current tools are perfect; there are problems like asymmetric dilation
that are not addressed. Measuring with a card, I think there's always
risk of parallax. Personally, my pupils have been measured anywhere
from 5.0 to 7.5mm (the largest measurement being with the Procyon but I
do not attribute it specifically to that as that measurement was the
only one where proper dark-adaptation protocols were followed).
I admit I'm a little biased against Colvard, because of adverse
opinions I've heard from doctors who have switched to Procyon. But I
don't really know. I think it won't be long before we see some more
studies out about pupil measurements with better information to judge
from.
Rebecca Petris
www.lasermyeye.org
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| Rebecca,
My apologies if I offended.
R
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| rebeccaNO_SPAM@lasermyeye.org 2005-03-19, 6:22 pm |
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r wrote:
> Rebecca,
>
> My apologies if I offended.
>
> R
You didn't! I'm very sorry if I came across otherwise!
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