Lasik Eyes Surgery - Your corneas are thinner if you get dry eye

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Your corneas are thinner if you get dry eye

Informer

2005-05-18, 11:47 am

Corneas already thinner and drier from LASIK are really in trouble
when you hit menopause, ladies. Please read

http://www.eyeworld.org/article.php?sid=2550

Post-menopausal women with dry eye have thinner corneas, study finds

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by Maxine Lipner Senior Contributing Editor

Some physicians not surprised by study results.

Research suggests that during menopause, some 3.2 million women may
suffer from dry-eye syndrome.
Because corneal thickness may be affected by dry eye, Juan A.
Sanchis-Gimeno, M.D., Ph.D., and investigators at the university of
Valencia, Spain, recently launched a study to determine if there is a
connection between the two conditions.
In the prospective study, which was published in the January issue of
Cornea, investigators compared the corneal thickness values of 30
post-menopausal women with dry eye with 32 post-menopausal women without the
condition.
Corneal thickness was determined with the Orbscan Topography System II
(Bausch & Lomb, Rochester, N.Y.). Investigators said that they used the
Orbscan instead of traditional ultrasound pachymetry because the pachymetry
would have required anesthesia, which could induce variations in corneal
thickness.
The investigators were comfortable with their choice because they felt
that when the cornea was measured with the Orbscan, it appeared thicker than
it did when it was measured with ultrasound pachymetry.
This would mean that if ultrasonic pachymetry readings were later to
be done by other researchers, they would be lower than those found when
testing with the Orbscan.

Shaping the study

The investigators determined that for those in the dry-eye group, mean
corneal thickness was significantly reduced.
The thinnest area in both groups was the central zone, which was 533.1
microns in the dry eye group and 547.63 microns in the normal eyes.
Meanwhile, the thickest portion was the superonasal zone, which was
632.43 microns in dry eyes and 648.78 microns in normal eyes. The thinnest
paracentral zone in both groups was the temporal zone, which was 578.7
microns among dry-eye patients and 595.44 microns for those with normal
eyes.
Investigators theorize that factors involved in the decrease in
corneal thickness may include increased tear-film evaporation from increased
osmolarity of the tears. They believe that decreased tear turnover may also
be increasing tear osmolarity and contributing to the phenomenon.
The investigators concluded that corneal thickness values were reduced
in post-menopausal women with dry eye.
As a result, increased caution should be used when selecting these
patients for refractive procedures such as LASIK for the correction of
residual errors following cataract surgery.

Differing views

Stephen C. Pflugfelder, M.D., professor, Department of Ophthalmology,
and director, Ocular Surface Center, Baylor college of Medicine, Houston,
who published a similar study in the July 1999 issue of Cornea, was not
surprised by the results.
"Our study showed that corneal thickness was decreased in dry eye in
general," he said. "I think that it's well established that corneal
thickness decreases in patients that have dry eye. The reasons for that aren't
really clear."
It would be useful if researchers' future studies include men, he
said.
"It would be interesting to compare women to men of that age and see
if women have even thinner corneas - something about dry eye that makes the
cornea thinner," he said. "It could be that there are some gender-related
differences in that, but the reason for that hasn't really been established
yet."
Currently, what is known is that dry-eye patients, as part of the
inflammatory cascade, develop higher levels of proteolytic enzymes that can
digest the tissue, he said.
"So, one possibility is that there are actually higher levels of these
enzymes that would thin the cornea," he said. "The other possibility is that
there are changes in the cells on the surface of the eye, in the epithelium,
that over time in dry eye does tend to also get thinner."
The study would have been more beneficial if it had been stronger,
said Samir A. Melki, M.D., Ph.D., clinical instructor, Harvard Medical
School, Boston.
"I would have liked to have seen a comparison between Orbscan
measurements and ultrasonic measurements," Dr. Melki said. "The
investigators just went with the assumption that Orbscan is better, while
the pachymetry would have been very easy to do and would have given us a lot
more information."
Indeed, the investigators may have made an erroneous assumption with
regard to Orbscan measurements, Dr. Melki said.
"They cite some studies [Journal of Cataract & Refractive Surgery,
November 1997; Cornea, November 2000; and Cornea, October 2001] in which the
Orbscan always has higher values than ultrasound, which is not what we see
in practice," Dr. Melki said.
In addition, Dr. Melki would have like to have seen follow up on these
patients following treatment for their dry eye.
John D. Sheppard, M.D., professor of ophthalmology, microbiology and
molecular biology, Eastern Virginia Medical School, Norfolk, said that the
study results were informative but unremarkable and expected.
"It makes sense that possibly with time, a dry-eye patient would
undergo more molding of the surface - perhaps a hypoplastic response of the
underlying stroma," Dr. Sheppard said. "However, I can't tell from the
article and their data whether or not the loss of thickness was stromal or
epithelial."
Confocal microscopy would have been useful in determining that, he
said. In the absence of this data, practitioners cannot be sure of the
significance of the study, he said.
"Clearly the idea of a thinner cornea in this population of patients
is important in selecting for refractive surgery," he said. "However, every
female, every post-menopausal female, and every dry-eye female is going to
have a pachymetry or Orbscan anyway for refractive surgery."
He sees the study results as a reinforcement of the need to obtain
precise pachymetry measurement in those who consider refractive surgery,
with both dry eye and corneal thickness playing key roles.
Hopefully, the study will remind surgeons to carefully examine
refractive surgery candidates for both conditions, he said.

Editors' note: Dr. Sheppard has a financial interest in Bausch & Lomb.
Drs. Melki and Pflugfelder have no financial interests related to their
comments.

Contact Information
Melki: 617-566-0062, melki@bostoneyegroup.com
Pflugfelder: 713-798-4732, stevenp@bcm.tmc.edu
Sheppard: 757-622-2203, jsheppard@vec2020.com

Glenn - USAEyes.org

2005-05-18, 11:47 am

A vast amount of the volume of the cornea is moisture of one kind or
another. Remove that moisture, and there will be a "collapse" of the
individual cells. Remove enough of that moisture, and long-term
damage can occur. This is a basic fact of the cornea, with or without
LASIK.

Anything that causes dry eyes beyond that which the individual can
tolerate is problematic and should be treated. We have a detailed
article on dry eye treatment at
http://www.complicatedeyes.org/dry_eye_treatment.htm Most information
relates to LASIK, IntraLASIK and dry eye, but the treatments are
nearly identical if the dry eye is naturally occurring chronic dry
eye, or temporary surgery- induced dry eye.

Glenn Hagele
Executive Director
USAEyes.org

"Consider and Choose With Confidence"

Email to glenn dot hagele at usaeyes dot org

http://www.USAEyes.org
http://www.ComplicatedEyes.org

I am not a doctor.