2 provides 'unprecedented' diagnostic readings
Ana Hidalgo-Simón MD, PhD
NICE - New technical progress suggests ultrasound diagnostic tools
may become the slit-lamp of the 21st century, Dan Z. Reinstein MD
told a clinical research symposium at the XX ESCRS Congress.
Dr Reinstein highlighted the potential of the new VHF Digital Ultrasound
Arcscan Artemis 2TM across a range of anterior segment applications.
With the ability to reveal sub-surface micro-anatomy within the
anterior segment and discern epithelial from stromal components
within the cornea, the instrument promises to be the 'crystal ball'
anterior segment surgeons have been waiting for, he said.
"No neurosurgeon would operate on a patient without a decent
MRI. In the same way, our most direct path towards proper surgical
management is going to come from the best and most accurate diagnostic
information before surgery," Dr Reinstein said.
He described the accuracy and precision of the measurements as "unprecedented".
M-scan studies within the cornea allowed investigators to determine
that the interface localisation precision of the system has less
than 1.0 micron of standard deviation (±0.87 µm).
This was shown experimentally to translate as the ability to make
measurements within the cornea with a precision of approximately
Scanning is performed in multiple meridians, therefore providing
data in 3-D. Based on this data, Dr Reinstein developed 3-D mapping
techniques for individual corneal layers before and after LASIK.
A new diagnostic tool promises to provide the most accurate preoperaztive
micro-anatomical information within the cornea for anterior surgeons,
according to a US ophthalmologist.
The new VHF Digital Ultrasound Arcscan Artemis 2TM allows measurements
to be made within the cornea with a precision of approximately 1.0
micron and 3-D scanning can be performed in multiple meridians.
It is also possible to determine the angle-to-angle or sulcus-to-sulcus
dimensions of an eye, with approximately 100 micron precision and
map these in 3-D for localisation of the largest axis, Dan Z. Reinstein
"We also spent considerable time developing other features
that are critical to using this technology as a surgical planning
device. For example, there is simultaneous optical infrared video
image of the eye with each ultrasound scan.
"This is a crucial element of the system because knowledge
of the position from which a scan was taken is important if scan
measurements are to be used for surgical planning, both for the
cornea and phakic IOL placement in the anterior segment," he
For LASIK surgery, the system has the advantage of being able to
detect the epithelial thickness separately from the stromal component
of the flap and from the residual stroma in 3-D.
All these measurements - with approximately 1.0 micron precision
and in 3-D - allow the creation of maps of the thickness of each
"This permits currently the most accurate planning of surgical
interventions and follow-up of the evolution of each corneal component
postoperatively. We can also determine very precisely the efficacy
of microkeratomes in 3-D - not just at one point," Dr Reinstein
In a study comparing central pachymetry by Orbscan with the Artemis
2, Dr Reinstein and colleagues found an estimated improvement of
25 microns (of standard deviation) in the accuracy of pachymetry
by Orbscan compared to the Artemis 2 technology with its state-of-the-art
This same study showed that 36% of eyes were significantly overestimated
by Orbscan, while 17% of patients were underestimated by Orbscan.
Patients overestimated could, in principle, be incorrectly deemed
to be candidates for LASIK, while some would be rejected on the
basis of an incorrect low thickness measurement.
"This is good for business on two fronts; good candidates are
not turned away, while patients with corneas too thin are detected
accurately" Dr Reinstein added.
Dr Reinstein has studied microfolds in Bowman's membrane and was
able to differentiate two sub-types: Bowman's cracks, possibly caused
by traumatic elevation or repositioning of the flap, and what he
called 'True Microfolds' which are actually grooves in Bowman's
caused by inadequate flap distension or repositioning.
He pointed out that although both lead to loss of best corrected
vision, the re-lifting of patients with Bowman's cracks will not
improve vision and could potentially worsen it. Therefore distinguishing
microfolds form cracks becomes very important.
Such studies also led to the modification of the flap handling to
a minimal-touch technique he called the 'door-opening' and 'door-closing'
He also discussed his group's findings regarding the wound healing
process within the cornea after LASIK and PRK, separating epithelial
factors from biomechanical factors. They found that the epithelial
response was unexpectedly complex. When they plotted the amount
of myopia treated against the epithelial power shift produced by
the surgery, they found that the epithelial response was non-linear
"At lower levels of myopia the epithelial power shift causes
more and more myopisation with the level of myopia treated. But
that is true only up to a certain point. Treating higher levels
of myopia, a paradoxical epithelial hyperopic shift appears to take
place," he reported.
The researchers concluded that the actual corneal power change in
LASIK is degraded by an average biomechanical shift of 15%. That
combines with the observed epithelial effect which accounts for
about an extra 5% of variation in the final postoperative refractive
"This comes to a possible total of 20%. The refractive errors
we are observing after LASIK can be explained by epithelial and
"And an understanding of these processes, combined with adequate
modelling and predictive calculations, will enable us to further
improve the accuracy of customised ablation procedures," he
There has been a tremendous amount of interest in the use of custom
ablation to repair corneas.
However, the epithelium tends to compensate for stromal surface
irregularities (it is almost always thicker in the 'crevices' than
over the 'bumps') and therefore the epithelium masks the true topographic
and/or wavefront error being caused by an asymmetric stromal surface.
According to Dr Reinstein, systems based on topographic guidance
have failed to adequately provide the surgeon with the accurate
tools needed to help these patients.
This new Artemis 2 technology also promises to improve the understanding
of the physiological dynamics of the anterior segment which will
have implications for the insertion of IOLs.
The instrument allows the measuring of internal dimension changes
from light to dark and during accommodation as the pupil and ciliary
body shift position. This could be particularly important for the
long-term safety of angle-supported or posterior chamber IOLs.
"In a study in which we looked at the correlation between white-to-white
measurements with sulcus-to-sulcus distances, we found no significant
correlation for myopic and hyperopic eyes.
"For angle-to-angle association with white-to-white measurements,
we found no correlation for myopes but a weak, though significant,
correlation in hyperopic patients. Unfortunately, hyperopic patients
are the least likely candidates for an angle-supported IOL,"
Dr Reinstein said.
In presbyopic insert surgery, Dr Reinstein pointed out that the
ability to accurately measure scleral thickness is going to be a
very important issue because the depth of implantation and position
of the implant relative to the lens equator are key success factors.
The scleral thickness and localisation of the zonular plane can
be accurately measured using a special software routine developed
specifically for this application.
"Using the optical image to ultrasound scan correlations, we
have developed special software that enables us to calculate the
exact plane on which the presbyopia inserts should be located to
achieve maximum effect," he explained.
Dr Reinstein is collaborating with Jack T. Holladay MD on developing
a new formula which will incorporate this improved measure of anterior
"We are dealing here with a technology which is enabling ophthalmologists
to see beyond the surfaces they have been examining in the last
few decades with microscopes. We are now entering an era of sub-surface
anatomy and micro-structure to better plan surgery and treatment
modalities," Dr Reinstein said.
The VHF Digital Ultrasound Arcscan technology, now embodied in the
Artemis 2, was developed at Cornell University by Dr Reinstein with
co-workers Ronald H. Silverman MD and D. Jackson Coleman MD.
Dr Reinstein, Dr Silverman and Dr Coleman have a financial interest
in Ultralink LLC, the company producing and marketing the Artemis
2. Artemis 2 has received US FDA approval and is commercially available.