SEEING PROGRESS
(continued from page 29)
and wavefront optimized treatments relied on the optical system
as a whole. This is based upon wavefront measurements that are
obtained by projecting an array of light beams into the eye and
then measuring the location of the corresponding light reflected
from the retina. The relative location of the spots is then used to
calculate the power of the optical system where light enters the eye.
Wavefront optimized treatments maintain a more natural corneal
shape by adjusting for the asphericity of the cornea based on anterior
curvature readings. Wavefront optimized treatments use more laser
pulses in the periphery of the cornea to minimize visual distortion
due to the curved shape of the cornea.
Wavefront guided treatments account for higher order aber-
rations. Briefly, higher order aberrations can be thought of as an
irregular astigmatism that include trefoils, “coma,” quadrafoils and
diffraction. Fortunately, they only account for a small percentage
of optical aberrations. Unfortunately, higher order aberrations can
result in very problematic vision and can not be treated by optical
devices such as contact lenses and glasses. For a short time, wave-
front guided LASIK was known as “custom” LASIK for this reason.
This did result in reducing higher order aberrations and improving
patient satisfaction by eliminating glare and halos with wavefront
guided LASIK. Therefore, custom wavefront guided LASIK became
the standard of care.
Topography guided ablation treatments for myopia gained FDA
approval in 2013. Topography guided LASIK differs from wavefront
customized LASIK in several ways. Measurement of the corneal
curvature does not rely on pupil size as wavefront measurements
do. This allows topography guided ablation treatments not to be
susceptible to pupil size changes, which can result in shifts of cen-
tering the treatment on the visual axis. Topography guided treat-
ments also allow correction of peripheral corneal abnormalities
where most higher order aberrations of the optical system arise.
These treatments address the irregularities in corneal elevation to
reshape the cornea into an ideal curve, resulting in excellent vision
and reduction of higher order aberrations. This was evidenced by
the T-CAT study performed in 2013.
The T-CAT study was a prospective study examining primary
LASIK eyes treating myopia with or without astigmatism. This
was a multi-center study with 249 eyes that were followed for 12
months. Notable visual outcomes include 30% of eyes having their
postoperative uncorrected visual acuity measuring 1 line better
than their preoperative best corrected visual acuity. Basically these
eyes were able to “see” 1 line better than they ever could with their
glasses or contacts. The T-CAT study produced excellent clinical
outcomes and refractive accuracy. As far as measurements go,
T-CAT produced high level of uncorrected visual acuity at 20/16
and even 20/12.5. Additionally, data from this study demonstrated
improvement in patient vision symptoms, including improvements
in light sensitivity and difficulty driving at night due to glare. This
30
LOUISVILLE MEDICINE
study was corroborated by other studies that examined topography
guided ablation profiles in one eye and wavefront optimized ablation
profiles in the other eye. Both produced excellent visual outcomes.
However, topography guided treatments did demonstrate better
contrast sensitivity, lower induction of higher order aberrations
and smaller amount of tissue ablation.
It’s already been demonstrated that the success rate of LASIK is
incredibly high and the complication rate for LASIK is extremely
low (complication rates as low as 0.3% and as high as 5.7%). Now
with the addition of topography guided LASIK, patients demonstrate
extremely high satisfaction rates (98.4% of patients in the T-CAT
trial stated that they would do it again). Generally, the quote that
I hear the most during a patient’s postoperative week 1 visit is “I
wish I would have done this sooner.”
Dr. Pattar is a practicing ophthalmologist with the Eye Care Institute.