November 2002

Design of IOL injectors is still evolving, according to surgeon

Many surgeons prefer to use an IOL injector, but currently available systems
need improvement, says one surgeon.

by Amy Krajacic

TUCSON, U.S.A. - Advances in small-incision technology now allow cataract
surgeons to operate through incisions smaller than 2.5 mm. Lens injectors
make this possible, but the current crop of commercially available injectors
could still stand improvement, according to a surgeon here.
Robert M. Kershner, MD, FACS in practice here, spoke about his current efforts to
improve IOL injector design.

"Certainly, foldable IOLs are the surgeon's preference today," Dr. Kershner
said. "Of all the lenses we implant, approximately 2.3 million are foldable
and about 1.3 million are nonsilicone, meaning that the majority are acrylic
lenses. Silicone still commands about 1 million lens implantations in the
United States, and these are predominantly three-piece lenses."

Existing injectors

IOL insertion methods for use in implanting foldable lenses employ either
folders or injectors. Folders are not ideal, Dr. Kershner said, because the
IOL must be handled, heightening the risk for contamination and damage of
the IOL.
Most surgeons prefer to use an IOL injector, which requires less handling of
the lens in a closed system with a smaller chance for contamination. Most
available systems, he said, require extensive lubrication of the injector
and the IOL to reduce friction and damage, and the capsular bag must be
inflated to accept the lens.
"To properly inject the lens, the IOL must be properly loaded, the injector
must accept the IOL in the proper configuration and the injector must work
consistently without damaging the lens," he said.
One drawback of using a microincision is the difficulty of inserting the
IOL, he added. The proper construction of the incision is crucial, and it
must be kept small; ideally, less than 3 mm and perhaps as small as 1.9 mm
and to allow entrance of the IOL injector.
"Incision architecture is critical to proper sizing for injectors, and we
have learned that a ratio of width to length of approximately 3:2 is ideal,"
Dr. Kershner said.
Existing IOL injection systems are strikingly similar and thus share similar
design flaws, he said. All current generic injectors require handling of the
IOL. It must be picked up out of its case and put into the injector.
Furthermore, the injection cannot be controlled.
Complicated instructions and difficult loading maneuvers also plague generic
injectors, according to Dr. Kershner. The plunger must contact the lens, and
the lens must be mechanically pushed out by the plunger, with potential for
IOL, haptic and optic damage, along with unreliable delivery into the eye.
The surgeon must use both hands to deliver the lens and center it, and he or
she usually cannot visualize the IOL during compression or insertion.
Finally, the surgeon must typically rotate the injector to assure proper
release and must manipulate the IOL after it is injected.
These factors result in an unacceptably high rate of failures with today's
injection systems, requiring the surgeon to remove the damaged IOL and abort
the procedure, Dr. Kershner said.

Ideal parameters

Dr. Kershner said that among the ideal design parameters for an injection
system, an easy-loading or preloaded system that allows one-handed use is
essential. In addition, friction and release should be controlled, and the
precision and reproducibility of the lens delivery without IOL damage should
be assured. The extent of handling of the IOL and the incision size required
for insertion of the injector tip is also important.
"A new IOL injector should have minimal parts, be disposable and easy to
manufacture, should allow one-handed operation and be reliable with precise
insertions without IOL or haptic damage," he said.
An ideal system should be compatible with incision sizes 2.8 mm or smaller,
and ideally should be preloaded so surgical team members do not have to
handle the IOL. The surgeon must be able to visualize the IOL at all times,
and must be able to control the insertion from start-to-finish without the
use of additional instrumentation.
Nothing should be manipulated while the lens is undergoing implantation, nor
should anything touch the IOL. A closed system, eliminating the potential
for contamination during lens implantation, should be used, and a
frictionless force should move the lens down without touching it. Ideally,
the lenses should be preloaded into the system, which will then safely
deliver the lens. The surgeon's only requirement should be to aim the system
into the eye, and have the technology inject and implant the lens.
"A simple-to-use, precise, reproducible IOL injection system is what we are
working on, one that is a completely unique design for an IOL injector that
will reliably and safely deliver the lens without failure," Dr. Kershner
said. "Even a 1% failure rate, in my book, is unacceptable. If you are doing
1,500 lenses a year, that is 15 torn lenses."

Robert M. Kershner, MD, FACS is an internationally recognized ophthalmic surgeon, innovator and teacher. He has published over two hundred articles, sixteen textbooks and is a consultant in the development of new technologies for cataract and refractive surgery. He can be reached at Kershner@EyeLaserCenter.com, Eye Laser Center, Suite 303, 1925 west Orange Grove Road, Tucson, Arizona 85704-1152 USA, phone: 520-797-2020 fax: 520-797-2235.