|
Home > Archive > Lasik Eyes Surgery > April 2005 > LASIK & Ectasia & CRSQA - The Emperor has no clothes
You are viewing an archived Text-only version of the thread.
To view this thread in it's original format and/or if you want to reply to
this thread please [click here]
| Author |
LASIK & Ectasia & CRSQA - The Emperor has no clothes
|
|
| gospa68@aol.com 2005-04-11, 6:14 pm |
| For those who have not been following the story on ectasia, it has been
the subject of hallway conversations for refractive surgeons since
1998. While ectasia is a great long term concern, it has not been fully
disclosed to unknowing potential refractive patients. The refractive
industry, as represented by the CRSQA, continues to argue that LASIK is
safe if at least a 250 micron residual bed is maintained. Others have
presented data showing that this is not true...a 250 micron bed is no
assurance of safety.
People can have their opinions but people can not have their own facts.
The facts continue to point to a potentially serious long term problem
for those who have had LASIK.
WK
A Guirao
Theoretical elastic response of the cornea to refractive surgery: risk
factors for keratectasia.
J Refract Surg, March 1, 2005; 21(2): 176-85.
PURPOSE: To explore the role that mechanical elastic factors may have
in post-refractive surgery corneal phenomena, from mild curvature
changes to keratectasia.
METHODS: The central cornea near the apex was modeled as an elastic
spherical thin shell loaded by the intraocular pressure (IOP).
Equations for myopic laser in situ keratomileusis (LASIK) were obtained
to estimate shifts and curvature changes of the posterior corneal
surface at the apex. The effect of every parameter was studied,
identifying potential risk factors for ectasia.
RESULTS: Theoretically, corneal thinning by ablation will produce an
elastic deformation of the posterior surface that depends on the
corneal parameters (curvature, Young's modulus, Poisson ratio, and
thickness), the IOP, and the ablation profile. In particular, a forward
shift and an increase in power of the posterior surface was predicted
for myopic LASIK, in agreement with previous experimental findings.
These changes rise non-linearly with the attempted correction, and are
greater for thinner preoperative corneas, higher IOP smaller Young's
modulus, and thicker flaps. Corneas with Young's modulus half the
average or less, or thickness <500 microm, may present high risk of
ectasia, especially for high IOP and thick flaps.
CONCLUSIONS: Some postoperative effects may be explained in part by
elasticity. Research efforts are needed to explain other biomechanical
behaviors. THE ACCEPTED CRITERION OF 250 MICRONS RESIDUAL BED IS
INSUFFICIENT for fine patient screening--depending on the individual
ocular parameters, it could be more restrictive. Advances in technology
are needed to create a preoperative examination including
two-dimensional maps of topography, pachymetry, and Young's modulus.
| |
| serebel 2005-04-11, 6:14 pm |
| Ectasia occurs very rarely in the scope of RS, but Wizzer here would
have you think that this is a common occurance. It does not.
SErebel
| |
| Ragnar 2005-04-11, 6:14 pm |
| You are just plain full of it. You must be Mr. Flap Melt. Nobody
else would dig so diligently to produce such fancy data that is
completely wrong.
On 9 Apr 2005 12:30:45 -0700, gospa68@aol.com wrote:
>For those who have not been following the story on ectasia, it has been
>the subject of hallway conversations for refractive surgeons since
>1998. While ectasia is a great long term concern, it has not been fully
>disclosed to unknowing potential refractive patients. The refractive
>industry, as represented by the CRSQA, continues to argue that LASIK is
>safe if at least a 250 micron residual bed is maintained. Others have
>presented data showing that this is not true...a 250 micron bed is no
>assurance of safety.
>
>People can have their opinions but people can not have their own facts.
>The facts continue to point to a potentially serious long term problem
>for those who have had LASIK.
>WK
>
>
>A Guirao
>Theoretical elastic response of the cornea to refractive surgery: risk
>factors for keratectasia.
>J Refract Surg, March 1, 2005; 21(2): 176-85.
>
>PURPOSE: To explore the role that mechanical elastic factors may have
>in post-refractive surgery corneal phenomena, from mild curvature
>changes to keratectasia.
>
>METHODS: The central cornea near the apex was modeled as an elastic
>spherical thin shell loaded by the intraocular pressure (IOP).
>Equations for myopic laser in situ keratomileusis (LASIK) were obtained
>to estimate shifts and curvature changes of the posterior corneal
>surface at the apex. The effect of every parameter was studied,
>identifying potential risk factors for ectasia.
>
>RESULTS: Theoretically, corneal thinning by ablation will produce an
>elastic deformation of the posterior surface that depends on the
>corneal parameters (curvature, Young's modulus, Poisson ratio, and
>thickness), the IOP, and the ablation profile. In particular, a forward
>shift and an increase in power of the posterior surface was predicted
>for myopic LASIK, in agreement with previous experimental findings.
>These changes rise non-linearly with the attempted correction, and are
>greater for thinner preoperative corneas, higher IOP smaller Young's
>modulus, and thicker flaps. Corneas with Young's modulus half the
>average or less, or thickness <500 microm, may present high risk of
>ectasia, especially for high IOP and thick flaps.
>
>CONCLUSIONS: Some postoperative effects may be explained in part by
>elasticity. Research efforts are needed to explain other biomechanical
>behaviors. THE ACCEPTED CRITERION OF 250 MICRONS RESIDUAL BED IS
>INSUFFICIENT for fine patient screening--depending on the individual
>ocular parameters, it could be more restrictive. Advances in technology
>are needed to create a preoperative examination including
>two-dimensional maps of topography, pachymetry, and Young's modulus.
| |
| Glenn - USAEyes.org 2005-04-11, 6:14 pm |
| CRSQA does not represent the refractive surgery industry. In fact, on
many occasions we are on the opposite side of industry.
Just because we don't support your "the sky is someday going to fall I
just know it even though there is no credible evidence that it is
going to happen and there is 40 years of evidence that it won't"
position on ectasia does not mean that we represent the refractive
surgery industry.
As to the issue that a 250 micron minimum untouched healthy cornea
will not develop ectasia; take that up with the FDA. They are the
ones who have affirmed this minimum and have promoted it as the
standard requirement in all refractive surgery related devices that
require FDA approval.
CRSQA does not make up these standards WizKid, we simply report them.
Deal with it.
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.
|
| |
|
|