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TECHNOLOGY
UPDATE Edited by Michael Colvard, MD and
Steven Charles, MD
An Update on
3-D Ultrasound
Will this
new technology carve a niche in refractive surgery?
Walter
Bethke,
Senior
Editor
By spring of next year, refractive
surgeons may have another option for measuring depth and irregularities of, not
only the cornea, but also its individual layers as well as the LASIK flap.
Here’s an update on some of the real-world applications of the Artemis 3-D
Ultrasound.
The
Artemis device sweeps a 50-MHz transducer in several arcs over the cornea.
Then, a computer digitizes the signal and 3-D software interprets it,
displaying such information as overall pachymetry, stromal thickness and
residual stromal thickness post-LASIK down to a resolution of 1
µm.
Daniel
Reinstein, MD, one of the device’s inventors, thinks the information the
device imparts is vital to performing the best LASIK possible. He likens
performing LASIK without the device to an orthopedic surgeon performing surgery
without an X-ray.
“It can tell you how cutting a flap affects the shape of the
cornea biomechanically,” he says. “It lets you predict how much
tissue will be left under the flap, and why a patient may not be exactly
perfect postop. The epithelium usually flows over irregularities, filling them.
But, in some cases, it can’t compensate for them, and topography
can’t measure it accurately, because the problem is below the
surface.”
He
cites the case of a patient he scanned in 1994 with the device. The wo-man had
undergone a well-centered ALK but had some regression and triplopia. The
corneal topography showed nothing unusual. The 3-D ultrasound, however, found a
large irregularity in the stroma due to an irregular cut. “The epithelium
had just about covered up the problem,” he says, “making the surface
of the cornea look regular. Internally, however, she had multifocal
optics.”
The
Artemis may also have potential to stave off corneal ectasia, which some
surgeons are reporting to be more common than they first thought.
“Anyone who’s done a lot of LASIK cases has seen
ectasia,” says Dr. Reinstein. He points out that the American Society of
Cataract and Refractive Surgery devoted an entire section to ectasia this past
year. “What if the flap you thought would be 160 µm turns out to be
220 µm? You may leave the cornea with only 190 µm, and you get
ectasia.” With the device, the surgeon would be able to obtain a corneal
thickness measurement at all points, not just the sampling done with normal
pachymetry.
When
phakic IOLs receive approval, the device will be able to give a
sulcus-to-sulcus and angle-to-angle measurement in any meridian in 3-D. This
may enable surgeons to reduce the risk of lens trauma and pupil ovalization
that can occur if the IOL is incorrectly sized.
Some may wonder, however, if
surgeons need such high-res imaging, at a cost of nearly $50,000, if LASIK
outcomes already appear to be good.
“Surgery is the alteration of
anatomy,” says Dr. Reinstein. “LASIK works very well and patients are
happy. However, it behooves surgeons to adhere to, and not ignore, the basic
tenet of ‘know the anatomy of the tissue on which you’re about to
operate, and know the effects you will have on it.’ Now we have a
diagnostic tool that will enable them to know exactly what happened.”
Artemis is still
awaiting FDA 510(k) approval, which George Wiseman, president of the
machine’s maker, Ultralink, expects by the second quarter of next year.
“By the time we have them ready to ship, we should have our
approval,” he says.
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