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Design of injectors is still evolving, according to surgeon
Many surgeons prefer to use an IOL injector, but currently available systems need improvement, says one surgeon.
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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, 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.”
For Your Information:
- Robert M. Kershner, MD, FACS, can be reached at Eye Laser Center, 1925 West Orange Grove Road, Suite 303, Tucson, AZ 85704-1152 U.S.A.; +(1) 520-797-2020; fax: +(1) 520-797-2235; e-mail: Kershner@asiteforeyes.com.