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Refractive Surgery
the difference isn’t in the thickness
in the lenticule because the edge of
any SMILE lenticule is always 15 µm.
Instead, it’s the center thickness of the
lenticule that differs between low and
high myopia. So, in a -1 myope the
center might be 15 µm thick, but in
a -9 patient it would be around 100
µm. It’s easier to see the center thickness
in the higher myopes. It’s just
the identification of the edge, and the
edges above and below the lenticule,
that the surgeon must be able to do.
With more experience, you are able to
identify the edges a lot more easily.”
Dr. Hjortdal says SMILE can also
involve some variation in the quality
of the lenticule cut, causing issues in
about 0.5 percent or less of patients.
“This is probably related to the early
stage the SMILE technique is in,
but there can be a little variation in
the completeness of the femtosecond
laser cut,” he says. “This means that
sometimes you may have a slightly difficult
lenticule removal and you might
induce traces of hazy tissue in the interface.
This may result in day-one
acuity not being as good after SMILE
when compared to LASIK, and you
can run into problems related to the
completeness of lenticule removal
and smoothness. Specifically, you may
have a little scar-like tissue in the interface
that results from you having to
be more aggressive in breaking these
small tissue bridges.
“However, even though we’ve experienced
such problems in some of
our 1,800 eyes, when we have a second
look at the patients in whom we
noted significant problems during surgery,
their condition seems to improve
with time,” Dr. Hjortdal adds. So, this
doesn’t end up in a situation of poor
vision for the patients.”
• Early vs. late postop vision.
Surgeons who have done both LASIK
and SMILE say they’ve noticed a difference
in the procedures’ patterns
of visual recovery. “At least in the beginning,
we felt there was a difference
between LASIK and this type of
surgery in terms of the uncorrected
visual acuity on day one being a little
lower with SMILE than what we’ve
seen with LASIK,” says Dr. Hjortdal.
“However, it would improve during
the first week. Today, though, I
think this has improved, due to the
experience of the surgeons and the
adjustments we’ve made to the laser
algorithm.”
Dr. Mehta has noted some differences
too, but in favor of SMILE. “Often
LASIK patients get immediately
good vision to start and then, over the
first year, they get a slight deterioration
in vision,” he says. “But with SMILE,
they get good vision and then it seems
to get better over that first year.”
• Retreatments. Surgeons have
been grappling with the question of
the best way to perform a retreatment
on a previous SMILE patient since
the procedure was introduced. “I
don’t think surgeons completely agree
on how to perform retreatments,” says
Dr. Hjortdal. “If you want to adjust
a diopter or so, it’s probably not wise
to do a new SMILE surgery, because
you’d need to do that SMILE in a
layer of cornea where you wouldn’t
interfere with the first cut. So, you’d
have to go deeper or more superficial.
Many surgeons—myself included—
perform a PRK with the excimer to
make minor corrections, if necessary.”
One approach that’s in its early
stages is a laser software modification
that allows the Visumax to turn
a SMILE into a LASIK by using a
circular pattern. “We did the first seven
SMILE enhancement eyes with
the circle software that converted the
SMILE cap into a flap,” says Dr. Shah.
“The software works by adding a laser
separation underneath the existing
SMILE cap. You then lift the flap
and use an excimer to perform the
treatment.” She says the downside, of
course, is you lose the benefits of flapless
SMILE. Dr. Mehta says one other
approach some have used is a thin-flap
LASIK. “Some surgeons have basically
done a LASIK with a 100-µm thin flap
on top of the SMILE cap,” he says.
“Before doing this, though, you’d need
to perform an anterior segment OCT
to make sure you have enough stroma
between where your ablation is and
where the lenticule was removed.”
• Hyperopia. The other arena in
which SMILE can’t compete with
LASIK, yet, is in hyperopia. SMILE
is currently only approved outside the
United States for myopic corrections.
The main challenge is the transition
zone on the edge of the lenticule. “I
know the company is studying how to
optimize the lenticule’s shape in order
to treat hyperopia,” says Dr. Hjortdal.
“This is because, when you treat hyperopia
with SMILE, you need to remove
a sort of doughnut-shaped piece
of cornea, and you need smoothing at
the periphery of the doughnut so as
not to have an abrupt change in corneal
thickness.” Dr. Mehta says regression
has been the main negative effect.
“Walter Sekundo’s group in Germany
has done some hyperopic treatments,”
Dr. Mehta says. “And they’ve found
they’re not as stable as myopic treatments.
There’s been regression in the
hyperopia. They’ve currently changed
some of the nomogram, so I hope to
be testing that out for them soon.”
Though SMILE has some areas that
could be improved, Dr. Mehta says it’s
moving in the right direction. “I think
LASIK is technically easier to do: You
just make a flap and the excimer does
the treatment for you,” he says. “With
SMILE, there is definitely a learning
curve with the technique in order to
recognize the planes of the lenticule,
visualization and the like. However,
instruments make a huge difference,
and the instrumentation for SMILE is
a lot better than it was when I started
three years ago. That’s been a big improvement.”
1. Ivarsen A, Asp S, Hjortdal J. Safety and complications of more
than 1,500 SMILE procedures. Ophthalmology 2013 Dec 20 pii:
S0161-6420(13)01064-6. doi: 10.1016/j.ophtha.2013.11.006.
[Epub ahead of print].
32 | Review of Ophthalmology | February 2014