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New rounded IOL edge design reduces glare
Barbara Boughton in San Francisco
GLARE is significantly higher in double square-edged IOL lens designs
than in hybrid lens edge designs, suggests laboratory research presented
at the annual meeting of the ASCRS.
Bradley Black MD and colleagues used a non-sequential ray tracing
to model the impact of IOL edge design on the distribution and intensity
of reflected and transmitted light rays. They found that the intensity
of light with both transmitted and reflected glare is much greater
with the double square edge IOL design.
"With the OptiEdge IOL (Sensar, AMO), light rays are dispersed
over the retina, which reduces the intensity of glare-and that's
what's important in whether a patient notices haloes or arcs of
light," he reported.
The posterior squared-off edge has long been prized because of its
ability to prevent opacification of the posterior capsule through
the mechanical barrier effect. But research by Jack Holladay MD
and others has also described the dysphotopsia that occurs with
the squared off edge, including glare, halos, shadows and arcs of
light.
"Rounding the edge of the optic causes greater dispersion of
the internally reflected rays of light, reducing intensity of edge
glare by 90 percent," Dr Black said.
Just how this translates clinically, however, is still an open question.
Dr Black noted that he has implanted many IOLs with double-square-edge
design and hasn't had to explant any. However, after several months
the investigators noticed a marked reduction in frequency of complaints
about glare from patients who received lenses with the OptiEdge
design.
When light rays hit a squared lens edge, the rays are displaced
to a nonvisiotopic part of the retina, forming a disturbed image.
Transmitted light rays are directed to areas other than the source
image, while reflected rays curve away. Both transmitted and reflected
light can contribute to glare.
The investigators found that when light hits the double-squared
edge lens at 23 degrees, there was little edge glare. But at 35
degrees, one begins to see arcs and intense tightly focused spots,
though very little transmission glare. Meanwhile, at 55 degrees,
transmitted as well as reflected glare becomes significantly more
evident.
In the OptiEdge's hybrid lens design, in which the posterior edge
is squared off but the anterior edge is rounded, the investigators
did not see any internally reflected rays at 23 degrees.
"Once you get to 35 degrees with the OptiEdge, you see that
the intensity of light is one third that of the double square edge.
And though internally reflected glare is still evident with the
OptiEdge, the amount is less at 35 and 55 degrees than with the
double-square edge," he said.
The researchers are now reviewing data on YAG rates and posterior
capsule opacification among patients with the OptiEdge lens. Other
studies do demonstrate that the OptiEdge does protect against opacification
of the posterior capsule, he stressed.
Randall J. Olson MD commented that edge glare may not be the only
important factor to consider with IOL design:
"The radius of the curvature of the implant has dramatic impact.
The flatter the implant, the more glare there will be. And increasing
the index of refraction will also increase glare."
His own study of 100 patients implanted with a frosted SA-30 lens
and the MA-30 lens showed that patients were much more satisfied
with the OptiEdge, and that glare problems were reduced with it.
In one patient with intractable dysphotopsia with an SA-60 IOL exchange
resolved his problem with a Sensar-E IOL.
"Frosting doesn't seem as good as the OptiEdge. Our data indicates
that the Optiedge is a design that works and still allows us to
have a square edge," Dr. Olson said.
Albert J. Galand, MD, questioned whether the Acrysof might be superior
in keeping the margin of the anterior axis over the optic. The anterior
sharp edge could have a role in keeping the anterior capsule in
place instead of sliding underneath the edge of the optic, he noted.
In response, Dr Black commented that OptiEdge lenses centre very
well, and, at the very least, show as little, if not less, tendency
than the one-piece acrylic lenses to decentre post-operatively.
Dr.
Bradley Black
drblack@eye.net
Dr. Randall Olson
John A. Moran Eye Center, Salt Lake City, Utah.
randall.olson@hsc.utah.edu
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