Exposing the LASIK Scam

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 Post subject: IOP measurements inaccurate after LASIK
PostPosted: Thu Jan 26, 2006 12:50 am 
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LASIK surgeons should be informing patients during the informed consent process that IOP measurements are inaccurate after LASIK. Falsely low IOP readings during eye exams can cause an eye doctor is miss dangerously high IOP, which can jeopardize patients' vision.


Cataract & Refractive Surgery Today
November, 2005

How Should We Measure IOP After LASIK?

http://www.crstoday.com/PDF%20Articles/ ... ose30.html


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PostPosted: Fri Jul 14, 2006 1:17 pm 
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OCULAR SURGERY NEWS EUROPE/ASIA-PACIFIC EDITION July 2006


Pre-LASIK measurements used to predict postop IOP

A statistical model was developed based on a constellation of preoperative conditions.

By Katrina Altersitz

Excerpt:

A statistical model to predict the true IOP after myopic LASIK has been developed by researchers in Taiwan. The formula uses preoperative measurements and other information to predict the amount of underestimation of IOP after LASIK due to changes in the cornea.

Accurate measurement of IOP after LASIK is important for the detection of ocular hypertension, said Chia-Ching Yang, MD, and colleagues at several institutions in Taipei, who published a paper on their predictive model in the American Journal of Ophthalmology.

People who have LASIK early in life have the risk of developing ocular hypertension or glaucoma later in life, when information on their refractive surgical procedure may not be available to health care workers. Measurement of IOP may be unreliable in these patients because of changes in their corneal structure during LASIK.



Read the entire article at: http://www.osnsupersite.com/view.asp?rid=17547

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"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato


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PostPosted: Wed Dec 20, 2006 1:34 pm 
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OCULAR SURGERY NEWS EUROPE/ASIA-PACIFIC EDITION July 2006

Pre-LASIK measurements used to predict postop IOP

A statistical model was developed based on a constellation of preoperative conditions.

By Katrina Altersitz
A statistical model to predict the true IOP after myopic LASIK has been developed by researchers in Taiwan. The formula uses preoperative measurements and other information to predict the amount of underestimation of IOP after LASIK due to changes in the cornea.

Accurate measurement of IOP after LASIK is important for the detection of ocular hypertension, said Chia-Ching Yang, MD, and colleagues at several institutions in Taipei, who published a paper on their predictive model in the American Journal of Ophthalmology.

People who have LASIK early in life have the risk of developing ocular hypertension or glaucoma later in life, when information on their refractive surgical procedure may not be available to health care workers. Measurement of IOP may be unreliable in these patients because of changes in their corneal structure during LASIK.

Dr. Yang and coworkers used information such as age, preoperative IOP and preoperative central corneal thickness (CCT) to create a linear mixed model to predict postoperative IOP.

"Significant predictors for postoperative IOP after myopic LASIK procedures included age, gender, preoperative IOP, ablation depth, CCT and preoperative spherical equivalent refractive errors,? the study authors said. ?The linear mixed model ? explained 91% of the variation of postoperative IOP.?

The study
Dr. Yang and colleagues examined 386 eyes of 193 patients.

Preoperatively, IOP was recorded on three office visits over 3 months. Postoperatively, ?at least two measurements of IOP for each eye were checked on the first day or during the first week immediately after LASIK,? the researchers said. Patients were followed for 3 months.

The LASIK procedures were standard, and all IOPs were measured with noncontact tonometry. The researchers said noncontact tonometry is particularly useful after LASIK because it is simple and safe.

?We averaged the three IOP measurements in each preoperative and postoperative visit to get the mean IOP for each eye for that visit,? the researchers said. ?The mean IOPs of all preoperative visits were averaged again to get the mean preoperative IOP. ? The mean postoperative IOP ? was calculated the same way.?

The IOPs were then correlated with the qualities measured before LASIK. The IOP underestimation was determined by subtracting the predicted postoperative IOP from the preoperative IOP. That number was added to the patient?s underestimated IOP postoperatively to find the true IOP.

?There was a pretty good fit between the observed and the predicted postoperative IOP,? the study authors said.

Results
?Although the underestimation of IOP after LASIK has been reported, awareness of recording IOP immediately after LASIK is often neglected in Taiwan,? the researchers stated.

The decrease in IOP after LASIK was statistically significant in this study, as it was in others, they said.

Additionally, they said, ?Ignorance of the underestimation of IOP resulting from LASIK procedure may not be a serious problem immediately after LASIK but will be particularly critical for subjects who undergo LASIK at a young age and have a high likelihood of developing glaucoma in old age.?

Based on age, gender, preoperative IOP, preoperative CCT, preoperative spherical equivalent refractive error and ablation depth, the researchers in this study concluded that they could accurately provide the predicted value of IOP immediately following LASIK.

For more information:
Tony Hsiu-His Chen, PhD, the corresponding author of this study, can be reached at the Institute of Preventative Medicine, College of Public Health, National Taiwan University, Room 207, No 19, Syujhou Road, Jhongjheng District, Taipei City 100, Taiwan; e-mail: stony@episerv.cph.ntu.edu.tw.
Reference:
Yang CC, Wang IJ, Chang YC, Lin LL, Chen TH. A predictive model for postoperative intraocular pressure among patients undergoing laser in situ keratomileusis (LASIK). Am J Ophthalmol. 2006;141(3):530-536.
Katrina Altersitz is an OSN Staff Writer who covers all aspects of ophthalmology.

_________________
Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato


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PostPosted: Wed May 07, 2008 10:17 pm 
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http://www.osnsupersite.com/view.asp?rID=28071

Quote:
Surgeons must be aware of glaucoma risk after refractive surgery
The risk of glaucoma after refractive surgery procedures should not be underestimated, according to one surgeon.

?I have to play the part of devil?s advocate by speaking about this topic in a refractive surgery meeting,? said Jos? Belda, MD, of Vissum Institute in Alicante. ?Still, we have to consider that what we see is only the tip of the iceberg. And below it, we may have a large quantity of patients presenting this problem in the future.?

The volume of refractive surgery is constantly increasing. Figures are difficult to estimate in Europe, but in the United States, about 1.4 million refractive procedures are performed per year, according to Dr. Belda.

?We must take into account that the largest part of refractive surgery procedures are done in myopic patients, amongst which the prevalence of glaucoma is three to four times higher than normal, even without any surgical procedure,? he said.

For glaucoma related to refractive surgery, surgeons must look at the causes, and these vary according to the technique used, Dr. Belda said.

One problem all techniques have in common is that true IOP levels are difficult to assess after surgery. IOP can be underestimated, and glaucoma can go undiagnosed for a long time, he said.

Surface techniques hold some advantages because no suction is applied during the procedure. But more corticosteroids are used to prevent haze, which may lead to corticosteroid-induced glaucoma, particularly in patients with high myopia, Dr. Belda said.

Meantime, suction can be a problem with LASIK. The vacuum phase is short, but pressure values are high ? between 60 mm Hg and 90 mm Hg ? and can reach as high as 200 mm Hg as the blade presses against the cornea, he said.

?Time is also surgeon-dependent. Inexperienced surgeons might prolong this stage and cause damage to the optic nerve,? Dr. Belda said.

There is no evidence to prove that this risk applies to normal eyes, but nobody has yet proved that this pressure increase is safe in eyes with underlying glaucoma or ocular hypertension, he said, adding that even less is known when femtosecond lasers are used for LASIK.

?We know that suction is lower, pressure is lower, but since the procedure is longer, we are going to flatten the cornea for a longer time than with mechanical microkeratomes, and so some damage can still be caused to the optic nerve,? Dr. Belda said.

He said he believes, however, that most cases of glaucoma after refractive surgery are related to the increase in IOP induced by the use of corticosteroids.

_________________
Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato


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