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Quality of vision improved with
ORK-W system
Roibeard O’hÉineacháin
in Rome
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Dimitrios
Siganos |
CUSTOMISED ablation performed with the Schwind Esiris laser excimer
and topography-based aberrometry does not appear to provide patients
with better visual acuity than standard Lasik – although it
may provide them with a better quality of vision, Greek researchers
say.
A study in which 100 patients underwent customised Lasik in one
eye using Schwind’s optimised refractive keratectomy (ORK-W)
system and standard Lasik in the other eye revealed no significant
difference between the two groups of eyes in terms of visual acuity,
Dimitrios Siganos MD told the 7th ESCRS Winter Refractive Surgery
Meeting.
The patients in the study had preoperative myopia ranging from -0.5
D to -10 D, with -0.25 D to 5.75 D of astigmatism. At a follow-up
of 12 months, 94% of eyes undergoing Lasik with the ORK-W system
achieved an uncorrected visual acuity of 20/20 or better, as did
93.1% of eyes undergoing standard Lasik.
However, 75% said they preferred their vision in their custom-treated
eye, while only 13% said they preferred their vision in the eye
which had undergone standard ablation.
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Corneal
wavefront measurements exported to ORK-W software |
In addition, three eyes in the customised ablation group which preoperatively
were unable to achieve a BCVA of 20/20 even with hard contact lenses
were able to do so postoperatively, with a gain of three lines of
BCVA.
In all eyes in the study, Dr Siganos used the Schwind pendular microkeratome
to produce the Lasik flaps and the Schwind Esiris excimer laser
to perform the ablations. All ablations had a 6.0mm optical zone
and a 1.25 mm transition zone.
Dr Siganos noted that the Esiris laser has a frequency of 200Hz
and produces a Gaussian beam with a spot size of 0.8mm. The laser
system has a 300Hz eyetracker and an integrated programmable patient
bed.
One particular advantage is the 29cm distance between the patient’s
eye and the laser, which makes it easier to manipulate additional
instruments such as the microkeratome.
The Schwind ESIRIS platform offers two alternative techniques for
customised ablations, he noted. The first is a selective corneal
aberrometry called optimised refractive keratectomy (ORK-Wavefront)
and is based on topography measurements with the Keratron Scout
topographer. The other is based on data provided by a wavefront
aberrometer such as the Schwind Tscherning Aberroscope.
Dr Siganos uses the topography-based aberrometry system, which only
provides data for the corneal aberrations rather than those of the
entire optical system.
“We preferred the topography-based system because it is easier
to use and most of the aberrations of the eye come from the cornea.
Another reason is that the changes in the crystalline lens which
occur with age induces changes of the wavefront aberrations making
the wavefront-based ablations less stable over time,” he explained.
The selective corneal aberrometry system derives a curvature map
from topographical measurements. It then uses the data to calculate
the wavefront error and incorporates it into the ablation profile
of the laser. The surgeon can select the laser shot file of a patient
from within the Esiris laser software.
Laser parameters like optical zone and target refraction are already
defined in the previous steps and no further data entry is necessary.
The rest of the treatment procedure is similar to standard treatments.
The ORK-W system may be particularly useful in the treatment of
difficult irregular corneas, the re-treatment of decentrations and
the enlargement of optical zones, he noted.
As an example of the usefulness of the ORK-W system in re-treatments,
Dr Siganos described the case of 45-year-old women who was over
corrected (+1.0 D) and astigmatic (–1.0 D at 66°). The
patient complained of double vision at night. By using the ORK-W
software, he was able to enlarge the optical zone and eliminate
irregularities of the previous treatment, with a marked reduction
in night-time symptoms, he said.
“The first clinical data is very promising. While we didn’t
find any statistical difference regarding refraction between the
standard ablation with the ORK-W, patients undergoing customised
ablation expressed better quality of vision.
“It may be that some people with many aberrations preoperatively
might benefit more from the customised approach. In any case, I
now routinely use the ORK-W system because not using it would be
like riding a horse when you have a space shuttle,” Dr Siganos
said.
Dimitrios
Siganos MD, PhD
Vlemma Eye Institute, Athens, Greece
Email: siganos@vlemma.com
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