41
EW REFRACTIVE
May 2018
Contact information
Reinstein: dzr@londonvisionclinic.com
Saad: dralainsaad@gmail.com
Santhiago: marconysanthiago@hotmail.com
Dr. Reinstein and his team
performed a retrospective analysis of
their entire database history, which
includes more than 15,000 patients
treated since 2002. If they had
applied 40% PTA as a cutoff, 26.5%
of their total database would have
been denied LASIK surgery, he said.
Seven patients had ectasia in one or
both eyes; of those, 70% had a PTA
of 40% or greater.
"This means PTA has a sensitivi-
ty of 70% and specificity of 73.5% in
our database, both of which are un-
acceptably low and certainly much
lower than the modalities described
above," he said.
Dr. Reinstein advocates for a
multifactorial screening approach
that includes all possible corneal
anatomical and morphological
features—front surface topography,
back surface topography, corneal
thickness progression and tomogra-
phy, and epithelial thickness map-
ping—combined with biomechani-
cal factors. With this approach, Dr.
Reinstein said PTA of 40% appears to
add little further information. How-
ever, he acknowledged, PTA could
offer a conservative safety marker for
surgeons who do not have access to
a full suite of diagnostics.
Dr. Santhiago added: "There
are some things that need to be
clarified. Ectasia is a rare condition,
which means that in any situation it
occurs rarely. What we have shown
is its higher incidence under the
conditions of high PTA. That was
clear. The robustness of an associa-
tion between a factor and an adverse
event is not measured through
sensitivity or specificity but through
odds ratio or relative risk. A risk
factor will never become a screening
method. Finally, if a high PTA is the
only risk factor and topography is
bilaterally normal, the patient could
have been submitted to surface
ablation." EW
References
1. Santhiago MR, et al. Association between
the percent tissue altered and post-laser in
situ keratomileusis ectasia in eyes with nor-
mal preoperative topography. Am J Ophthal-
mol. 2014;158:87–95.
2. Santhiago MR, et al. Role of percent
tissue altered on ectasia after LASIK in eyes
with suspicious topography. J Refract Surg.
2015;31:258–65.
3. Santhiago MR. Percent tissue altered
and corneal ectasia. Curr Opin Ophthalmol.
2016;27:311–5.
Editors' note: The physicians have
no financial interests related to their
comments.
