Philadelphia-The
Sovereign WhiteStar system is a revolutionary "cold"
phaco technology that is unique in its ability to
emulsify the most brunescent nuclei without any risk of
a wound burn, according to David F. Chang, MD, who
reported on his experience with WhiteStar (AMO, Irvine,
CA) here at the annual meeting of the American Society
of Cataract and Refractive Surgery.
"Cold phaco is a
prominent topic this year, because in the United States,
we can now purchase at least three different 'cold'
phaco systems. In addition to WhiteStar, both laser
phaco and sonics (Staar Surgical) are pure cold phaco
systems that allow us to remove the lens without any
significant heating of the phaco tip," said Dr. Chang,
clinical pro-fessor of ophthalmology at the University
of California, San Francisco and is in private practice
in Los Altos, CA.
"The promise of cold
phaco has always been twofold. First, we would like to
improve safety, by eliminating the risk of a wound burn
and by decreasing the amount of energy introduced,
which, in turn, might lessen endothelial trauma," he
said. "Second, bimanual phaco would become possible if
the coaxial irrigation sleeve were no longer needed to
cool the phaco tip," Dr. Chang explained. He has
performed more than 700 cases using the WhiteStar
system.
However, Dr. Chang
asserts that we should use brunescent nuclei as the true
test of the benefits of any new phaco technology.
"These cataracts
challenge us with a poor red reflex and a greater risk
of wound burn, endothelial cell loss, and posterior
capsule rupture," he said. "Therefore, these are the
cases where we want to have any additional help that new
technology can give us. This is why it has been
disappointing that neither laser phaco nor sonics is
effective for re-moving denser lenses."
WhiteStar can handle
the brunescent lens because it still delivers full-power
ultrasound. Clinically significant heat is prevented by
a new paradigm of pulse mode. Dr. Chang calls this
"hyperpulse" because the pulse rates are on the order of
ten times more than those traditionally used. In
addition, the ratio of the phaco "off" versus the phaco
"on" duration can be set at 4:1, compared with
traditional pulse, which is 1:1. In other words, the
pause between pulses is four times as long as the
individual pulses.
"It is this dramatic
increase in the frequency and duration of the rest
periods that keeps the tip cool," Dr. Chang explained.
"This has led to overall reduction in average equivalent
phaco time (EPT) compared with non-WhiteStar cases using
the same technique, machine, and settings.
"An unanticipated
benefit of hyperpulse is a dramatic increase in nuclear
followability," Dr. Chang reported. "This is
particularly obvious with brunescent lenses, where there
is typically excessive chatter and turbulence. This is
because rigid fragments cannot mold into the mouth of
the phaco tip and are kicked away by the increased
stroke lengths that define higher phaco power.
"This increased
turbulence of nuclear particles may be a significant
factor in the greater endothelial cell loss that occurs
with brunescent lenses," Dr. Chang concluded.
Because the
ultrasound is interrupted so frequently with WhiteStar,
the overall repelling force of the vibrating phaco tip
is drastically reduced, which allows the vacuum to hold
material at the tip better. "This decrease in chatter
and turbulence is probably much safer for the
endothelium in these challenging cases," Dr. Chang
noted.
Dr. Chang presented a
consecutive series of the first thirty brunescent 4+
lenses he removed using the WhiteStar system.
"The range in EPT was
from 6 to 30 seconds. The average EPT for the 30 lenses
was 9.1 seconds, using a vertical phaco chop technique
with no sculpting," he reported. "The primary clinical
difference in these brunescent lenses was clearer
corneas immediately postoperatively than I was
accustomed to, using the same Sovereign handpiece and
fluidics without WhiteStar. I attribute this to the very
obvious improvement in followability with
WhiteStar."
Dr. Chang noted that
while bimanual phaco may be of limited value until
paracentesis-injectable IOLs are developed, WhiteStar
offers important advantages for conventional
phaco.
"Besides reducing the
EPT, and eliminating the risk of wound burn, the
reduction in particulate turbulence with dense nuclei is
safer for the endothelium," Dr. Chang concluded. After
so much research has gone into alternatives to
ultrasound energy, he suggested that it is ironic that
hyperpulse ultrasound seems to be the best "cold"
technology yet.