| Glenn - USAEyes.org 2005-11-30, 10:59 am |
| Bill,
Schallhorn has been discussed extensively in this forum as well as
elsewhere. His landmark study has certainly created controversy and
your studies have refuted the suggestion that pupil size does not
matter, but I disagree that this is what Schallhorn actually has said.
In fact, he has not said this at all and recently in a trade article
he again affirmed that he has never said, nor does he believe, that
pupil size does not matter.
What Schallhorn's and subsequent studies have shown is that pupil size
ALONE is a poor predictor of who will and who will not get night
vision problems (NVP) after refractive surgery.
This really is not something new. Even a casual industry observer
knows of cases where a patient with a large pupil and a smaller
ablation did not develop NVP. On the narrow examination of the pupil
size = NVP issue, Schallhorn is correct. There is not a direct
correlation.
The fact that pupil size alone does not reliably predict who will and
who will not develop NVP does NOT by the wildest stretch of the
imagination mean that pupil size does not matter. It matters and it
matters a lot, but it is not the only factor that matters.
As more refined studies have shown, the pupil size compared to
ablation size when combined with other factors such as amount of
tissue removal (i.e. amount of correction) does tend to indicate who
will develop NVP, but even then there is no consistently reliable
formula for prediction. Every once in a while people who "should" get
NVP don't and people who "shouldn't" actually do.
What has happened is that many people for reasons that range from
benign to nefarious have taken Schallhorn's paper and said it meant
that pupil size does not matter. This is not what his paper says, and
when you ask Dr. Schallhorn directly it is not what he says it says.
It is not Schallhorn who says pupil size does not matter...it is
others who say that Schallhorn's study says pupil size is unimportant.
I suggest those individuals listen to the author. Schallhorn himself
in public, to me privately, and quoted in the trades says that pupil
size IS important.
As you have eloquently shown, the pupil size issue is one of relative
risk. Yes, someone with a large pupil and a small ablation has a
higher probability of developing NVP, but if the refractive error is
low that probability is diminished.
Of course you and I are more on the conservative side of the issue. We
both have stated that whenever the optical ablation zone is smaller
than the size of the naturally dilated pupil, the patient has an
elevated risk of developing night vision problems. An elevated risk is
not an absolute, but it most certainly is elevated.
For more on the issue of pupil size, see
http://www.usaeyes.org/faq/subjects..._pupil_size.htm
And yes, "Eye" is so off target that it would be truly laughable if it
were not so pathetic.
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.
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