FEMTO-LASIK and BEYOND - Carl Zeiss, Inc.

June 2012 Supplement
7
we normally use an S cone if it is a 12-2 or 12-3 mm
cornea. With an M cone, it is a little easier to get suction
breaks,” she said.
VisuMax vs IntraLase LASIK: She discussed the retrospective,
multi-surgeon study of LASIK performed for myopia
with or without astigmatism from September 2009 to
April 2010 at SNEC. According to her, the efficacy index,
predictability and safety were similar for VisuMax (n=882)
and IntraLase (n=654). The VisuMax seemed to be much
better in high myopes (-10D or more) with an efficacy index
of 0.97 (n=8) as against the IntraLase with an efficacy
index of 0.84 (n=9). “But the numbers are small and we
may have confounded the results,” she cautioned.
VisuMax vs IntraLase, Contralateral Eye Study: The
prospective randomized study consisted of a bilateral
simultaneous LASIK with VisuMax 500 kHz femtosecond
laser for LASIK flap creation in one eye and IntraLase
femtosecond system in the fellow eye. Excimer laser
ablation was done with Wavelight® Allegretto 400 kHz
in both eyes. The patients and surgeons were interviewed
perioperatively with a standardized questionnaire
about their operative experiences and preferences. Dr
Chan shared the results of 24 patients of the 40 target
population. Despite of the VisuMax being a low pressure
system, 17% had a loss of light perception during suction
and during the femtosecond pass. The same was seen
in around 45% with IntraLase. When questioned about
the fear factor, 46% of the VisuMax patients and 67% of
IntraLase patients were frightened during vacuum suction
or applanation. “Most patients said that the vacuum
suction for both the systems was the most painful part.
The pain score for VisuMax was 1.7 and for IntraLase
was much higher (4.3),” she said. Seventy-five percent
and 2% of patients preferred the VisuMax and IntraLase,
respectively. The patients disliked the discomfort and pain
in IntraLase and the constant stare at green light in the
VisuMax. According to Dr Chan, she finds the VisuMax
to be “an easier platform” with lesser subconjunctival
hemorrhage and suction loss. “About 45% of us felt that
the IntraLase was easier to lift, 17% found VisuMax was
easier to lift and 37% are had no preference,” she said.
Conclusions: Dr Chan concluded that a nice and assuring
upward trend in predictability has been obtained with the
VisuMax. She feels that the VisuMax is also a preferred
choice by patients. Loss of light perception occurred more
frequently with the IntraLase during flap creation. “Since
its inception in November 2008, SNEC has developed
successful Femto-LASIK with VisuMax program. Good
clinical outcomes for myopic LASIK have been achieved
with excellent safety, predictability and efficacy profiles,”
she summarized.
Dr Patrick Versace on “Registration,
Alignment and Tracking”
“ZEISS provides us with a platform
that effectively has three elements of
a laser delivery system. It has good
diagnostic, so we can measure corneal
shape, we can measure the wavefront
of the cornea and total eye, and these
things are integrated into the
CRS-Master. We can plan treatments
integrating all the data that we collect.”
Ablation, rotational alignment and tracking: “Zeiss
system tracks both the pupil and the limbus. It has
a sampling speed and a response time,” Dr Versace
said. He showed the impact of change in tracking speed on
various parameters.
Dr Versace specified how it was important to “put the ablation
where it is meant to be on the cornea and to maintain
that position throughout the treatment.” He agreed that
success was in “having the device placed on the visual axis
not on the pupil center.”
Talking about an acceptable misalignment he said that a
translational error of 300 μm to 400 μm and a rotational
error of 8-10 degrees would still give a 50% reduction in
higher order aberrations. He said that a workable registration
would be an XY shift of less than 200 μm and a
rotational alignment within 5 degrees. He then spoke about
the wavefront alignment with the Zernicke reference and
how the pupil was used for wavefront capture. According
to him, the ZEISS system does compensate for the shift in
center of the pupil as the pupil dilates or gets smaller. “The
ZEISS platform has a resolution of 100 μm with pupil
center shift. That is well within what we need.”
Angle kappa: Describing how a large angle kappa leads
to a significant induction of coma, he shared the results
for angle kappa from a recent study done in Iraq which
unleashed that the angle kappa was common and the values
were pretty much the same for all refractive errors, myopia
and hyperopia.
Cyclorotation: Referring to rotational alignment and astigmatism,
Dr Versace spoke about “how much cyclorotation
occurs when the patient goes from sitting to lying down.”
“Most patients have less than 5 degrees cyclorotation,” he
said. Dr Versace showed the WASCA/CRS-Master/MEL 80