May 2014

 

CATARACT

 

Device focus

IOL cutters: What goes on behind development


by Michelle Dalton EyeWorld Senior Contributing Writer

 
   

The Snyder/Osher forceps (left) have channels on the inside of the rectangular jaws that hold the IOL optic firmly during cutting. The scissors (right) have fine serrations that grasp slippery IOL materials during each cut. The scissors have a rounded tip.

Source: Michael E. Snyder, MD

The blades of the Packer/Chang IOL cutter are shown incising a lens. A new, single-use, disposable version is scheduled for release this year.

Source: Mark Packer, MD

EyeWorld spoke to several physicians whose names adorn IOL scissors to find out how they took concept to reality

Most surgeons do not expect to remove the IOL that they are implanting during cataract surgery, but there are some cases where that must be done. "I'm often asked to name the best IOL, and my response is that it's the one that's easiest to remove when the next best lens comes along," said Richard Mackool, MD, founder of the Mackool Eye Institute, New York.

Surgeons must make several intraoperative decisions when explanting a lens, Dr. Mackool said, including whether or not to remove or amputate the haptics, how many segments to divide the IOL into, when viscodissection is adequate, and how and in what location to insert the new IOL. "Happily, the surgical need for IOL removal or exchange is uncommon," he said. But when the situation does arise, a key component to the surgery is the choice of IOL scissors/ cutters. EyeWorld spoke to several surgeons whose names adorn these instrumentsand here are their stories (in alphabetical order).

Mackool Foldable Lens Removal System

Before the advent of the Mackool Foldable Lens Removal System (Impex Surgical, Brooklyn, N.Y.), relatively large profile instruments and a correspondingly large incision were required to simultaneously fixate and explant an IOL, Dr. Mackool explained. "Often there wasn't adequate space in the anterior segment for both the implant and the instrument." So, about 8 years ago, Dr. Mackool "thought it would make more sense to use two smaller instrumentsone a small forceps inserted through a sideport incision and used to fixate the IOL, and the other a microscissors that fits easily through any phaco incision of 2 mm or greater that would cut the implant in half."

Dr. Mackool added "teeth" to the distal end of both the scissors and forceps so that after the IOL was cut, either instrument could easily grasp and remove each segment. "The ease in freeing the haptics is the factor in determining whether to remove or amputate them," Dr. Mackool said. In general, the haptics become as tightly encased within the capsule as they are going to become by 4 to 6 weeks. He and his son, R.J. Mackool, MD, have previously reported that removal of the lens epithelium from the undersurface of the anterior capsule by vacuuming will delay the process for several months. Finally, Dr. Mackool said the biggest difference between silicone and acrylic lenses is that the former are "slippery" with a thinner optic edge but a thicker central optic. "Forceps tend to slide off them easily and forceps with teeth tend to cut through them," he said, adding he often uses a microhook placed on the opposite side of the optic to fixate the IOL as the scissors are used to divide it.

Packer/Chang IOL cutters

Like most innovations in cataract surgery, the Packer/Chang IOL cutters (MicroSurgical Technology, MST, Redmond, Wash.) were developed because of limitations, said co-designer Mark Packer, MD.

"In this case, the initial inspiration was microincisional cataract surgery," he said. "I had started performing 1.4 mm biaxial phaco, and there weren't any instruments that could easily fit through that wound size."

Dr. Packer approached Larry Laks (from MST), who "was the glue that put it all together. [David Chang, MD] and I were both working on similar ideas, but we had no idea what the other had been doing until Larry brought us together."

Dr. Packer worked on the size element of the scissors, while Dr. Chang wanted to ensure the scissors "were able to cut through anything." At the time, they were both implanting the ReZoom (Abbott Medical Optics, Santa Ana, Calif.), and the acrylic material "was at the time the hardest foldable material marketed. Most scissors got the lens material caught between the jaws instead of cutting the lens." According to Dr. Packer, MST developed a scissor that could cut through that acrylic material without bending the blade. Dr. Packer said that concept to final, marketed instrumentation took close to 3 years, but most of that time was trying to find the right manufacturer. "The whole idea didn't gain traction until Larry came on board, and from there and with David's interest, it took about 6 months."

Ironically, the scissors then became part of the Synchrony IOL (Visiogen/Abbott Medical Optics) clinical trial, as the protocol demanded that if the lens was not stable in the bag, it had to be explanted. For any burgeoning instrument developers, Dr. Packer recommends developing a concise mission statement and (if remotely talented) "sketch what you envision." Otherwise, it may be difficult for manufacturers and/or colleagues to understand the concept. "Show it to everyone. See who's interested. There are no proprietary rights in instruments. No one's going to patent it," he said.

Snyder/Osher IOL Explantation Set

Working through smaller incisions successfully was the driving force behind the Snyder/Osher IOL Explantation Set (Geuder, Heidelberg, Germany), said co-designer Robert H. Osher, MD, in practice at Cincinnati Eye Institute. "We wanted a set of scissors and forceps that would serve multiple purposes," he said. "Our design allows for the scissors to cut at right angles, at 45 degrees, straightaway, and backward."

The scissors have interchangeable handles and can be switched from vertical to horizontal rotation to cut, he added. Michael E. Snyder, MD, in practice at the Cincinnati Eye Institute, added: "We wanted to make sure that we could work through a 2.2 mm incision, so we wanted the jaws of the scissors to be long enough that we could make some reasonable progress across the lens per cut. But they had to be short enough so when they were open inside the eye with the cross point of the scissors being in the wound, we had a margin of safety from the cornea and the capsule."

He credits Dr. Osher with emphasizing the length from the hinge point to the tip of the scissors as a key to be able to maximize the distance per cut while minimizing the "wideness" of the jaw opening for the protection of the capsule and the corneal epithelium. "On older scissors, the distance from pivot point or hinge to the end of the scissors tip was much longer and that made it more awkward to work through the smaller channel," he said.

Dr. Snyder prefers a "one size fits all" approach, so he wanted to ensure the scissors could cut easily through silicone, acrylic, or, rarely, collamer. The Snyder/Osher scissors incorporate a serrated edge to better grasp the slippery silicone and collamer lenses. They wanted to minimize the blade thickness because the thinner a blade, "the more it's going to slip past the trailing portion that's been cut and less likely to push that trailing portion up or down, so the less likely to contact either the endothelium or the capsule and the greater the therapeutic safety window," Dr. Snyder said.

While serration is more important when explanting silicone lenses, an added benefit Dr. Snyder incorporated into the design was a rounded tip "so that the scissors wouldn't inadvertently catch or snag the capsule or the iris tissue."

Dr. Osher said it's the one set that's "always on my tray."

Both men recalled the time from concept to commercialization as being "a few months," and said it is much easier to bring an instrument to market than a device or drug.

"There are other ideas out there," Dr. Osher said. "Just persevere if you believe in it."

Editors' note: The physicians have no financial interests related to the products mentioned.

Contact information

Mackool: mackooleye@aol.com
Osher: rhosher@cincinnatieye.com
Packer: mark@markpackerconsulting.com
Snyder: msnyder@cincinnatieye.com

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