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Latest accommodating IOL design shows promise
It took 10 years to arrive at the present design. Initial clinical results are encouraging.
ALISO VIEJO, U.S.A. — After a decade of research and development and almost as many lens designs, J. Stuart Cumming, MD, and colleagues have devised an accommodating IOL that manages to move forward to accommodate without dislocating.
“Of this seventh design, we have 185 implants and there have been no dislocations. The centration is excellent, I believe, because the ciliary muscle is paralyzed with atropine and constriction and relaxation of the muscle during the period of fibrosis of the capsular bag is the main reason that lenses decenter,” Dr. Cumming said. Dr. Cumming is chief scientific officer of C&C Vision, which is developing the accommodating lens.
Since 1991 Dr. Cumming has been collaborating on the lens with Jochen Kammann, MD, of Germany. “He implanted seven different lens designs before the final design was selected,” Dr. Cumming said.
Bilateral implantation
Arturo S. Chayet, MD, implanted this newest design in 14 patients bilaterally in Tijuana, Mexico. Of those patients, 79% are 20/30 and J3 uncorrected, and 100% are 20/40 and J3 uncorrected. “More importantly, if we look at the corrected distance vision without an add, 93% of the patients are 20/25 and J3,” Dr. Cumming said.
Dr. Cumming described the theory of how the lens functions. “When plate lenses are placed into the capsular bag, the anterior capsule fibroses and applies end-to-end pressure on the plates, which vault. The lens can’t vault anteriorly because of the fibrosed anterior capsular rim, so it vaults posteriorly and the optic comes to lie up against the vitreous face. When the ciliary muscle constricts, it redistributes its mass like any other muscle and encroaches on the vitreous cavity space, increasing the vitreous cavity pressure. We think this moves the optic forward,” he said.
The history
---J. Stuart Cumming, MD, and colleagues have devised an accommodating IOL that manages to move forward to accommodate without dislocating.
About 10 years ago, Dr. Cumming implanted a large number of plate lenses and noticed that some of the patients who were virtually plano could see at distance and near without glasses, and this intrigued him. “So I put these patients behind the phoropter, and refracted them with maximum plus, giving them their best corrected distance vision. Then I put a reading card in front of the phoropter and dimmed the lights in the examining room and I found that a few of these patients could still read under these circumstances. We had eliminated the possible pseudo-accommodative effects of myopia, cylinder and a small pupil,” he said.
A literature search familiarized Dr. Cumming with work on ciliary muscle action and accommodation done by Busacca in 1955 and Coleman in 1986. Further research demonstrated that a plate lens is “shrink wrapped” during fibrosis of the anterior capsule and the optic forced posteriorly to lie up against the vitreous face.
“Armed with this logic, a series of lenses were designed to take advantage of pressure changes in the vitreous cavity,” he said.
Dr. Cumming explained that immediately after implanting the accommodating lens, the ciliary muscle is paralyzed with a drop of atropine to prevent the intermittent increases of vitreous cavity pressure from moving the optic forward. This allows the optic to center well and fixate in its most posterior position during fibrosis of the capsular bag.
Current design
The most current design is characterized by semi-rigid plates with a hinge across the plate adjacent to the optic. The overall length of the lens, plate tip to plate tip, is the same as standard plate silicone lenses, 10.5 mm, with polyamide loops making the overall length 11.5 mm. In order to get more leverage and therefore more movement of the optic, the plates were lengthened by making the optic 4.5 mm.
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The lens with this design, after implantation and paralysis of the ciliary muscle with atropine, becomes the anterior wall of the vitreous cavity space. This leaves the optic, with its adjacent grooves, as the section of the vitreous cavity wall with the least resistance to an increase in vitreous cavity pressure, which occurs on constriction of the ciliary muscle. An increase in vitreous cavity pressure thus moves the optic forward; 1 mm of movement is equivalent to almost a 2 D power change.
“The initial clinical results are very encouraging,” Dr. Cumming said. “After 14 patients were implanted bilaterally, none need glasses and they can all see well at distance, intermediate and near.”
For Your Information:
- J. Stuart Cumming, MD, can be reached at C&C Vision, 6 Journey, Ste. 270, Aliso Viejo, CA 92656 U.S.A.; +(1) 949-916-9352; fax: +(1) 949-716-8362. Dr. Cumming is chief scientific officer for C&C Vision.