New silicone IOL accommodates, say inventor, clinical researcher

Issue: December 1996

DORTMUND, Germany—A new silicone IOL design incorporating hinged plate haptics provides accommodation by allowing the lens optic to move forward upon constriction of the ciliary muscle, according to the lens designer and the surgeon who has implanted prototypes of the lens.

J. Stuart Cumming, MD, of Anaheim, Calif., holds U.S. patents 5476514 and 5496366 on the novel accommodating silicone IOL design, which he has licensed to Medevec BV of Amsterdam. Fifty-five prototypes of the IOL have been implanted by Jochen Kammann, MD, in his practice here. The lens, manufactured by Medevec BV, has a 5 mm optic with hinged attachments to relatively narrow plate-style haptics. At an average follow-up of just more than 2 years after implantation of the second prototype of the lens, five eyes examined were measured to have accommodative amplitude between 1.75 and 3.5 D, depending on the method used to assess accommodation.

Birth of the concept

The idea for the accommodating IOL came to Cumming based on his observations of conventional plate-haptic IOLs as well as the anatomy and physiology of the eye.

"I had implanted about 2,000 plate-haptic silicone lenses and I noticed that they always located in the posterior part of the capsular bag, which is 5 mm from front to back," Cumming said. "Silicone lenses are only 1.3 mm thick, so there is a very large space in front of the plate lens. It occurred to me that you could place a hinge in the plate haptic near its junction with the optic. That would make it possible for the optic to flex forward with accommodation, providing the ciliary muscle was initially paralyzed to allow fibrosis to fix the IOL in the distance position.

"In reviewing textbooks on ocular physiology, I found an article that described an increase of vitreous pressure resulting from encroachment of the ciliary muscle on the vitreous space during accommodation," Cumming continued.

The combination of posterior vitreous pressure on the IOL and ciliary muscle constriction squeezing the hinged haptics seemed likely to move the optic enough to shift from far to near focus.

"Only a very small movement is needed to provide accommodation because the plate lens locates so far posteriorly," Cumming said. "A movement of less than 1 mm will provide 2 D of accommodation.

"With this knowledge I designed a simple lens and we implanted two of them in England in 1991. One patient died of natural causes within 3 months of surgery, and I traveled to England several times to follow up the other patient. I found that she was accommodating about 3 to 4 D."

Around that time, Cumming met Kammann, who was also implanting only silicone lenses. The two decided to collaborate.

"The lens is easy to implant," Kammann said. "It can be folded and implanted through a 2.5- to 2.8-mm incision. You can use a clear corneal or corneoscleral incision; you can use the temporal approach — whatever you prefer. However, the IOL obviously must be in the capsular bag in order for the design to work, and it is very important to remove all the viscoelastic at the end of the procedure."

Fibrosis affects function

Postoperative capsular fibrosis and contraction also play important roles in the successful use of the IOL. The lens is manufactured with its optic and haptics in the same plane, but postoperative anterior capsular contraction results in a posterior vaulting of the lens. Thus vitreous pressure is necessary to move the lens forward.

Additionally, to prevent ciliary muscle activity from fixing the lens in the forward, accommodative position and from decentering the IOL before capsular fibrosis can fix it in the bag, the ciliary muscle must be paralyzed with one drop of atropine at the end of surgery and again daily for 3 weeks postoperatively.

"It takes about 10 to 14 days for the atropine to wear off, so the patient is dilated for about 4 to 5 weeks," Cumming said.

Although the period of pupillary dilation is inconvenient, Kammann reports that patients found the eventual result well worth it.

"We explained the benefits of the IOL, and patients were very happy that they could have their accommodation back," he said.

Measuring accommodation

Accommodative amplitude was measured in two ways. First, patients were corrected to their best vision in a dim room (to avoid the increased depth of focus created by a small pupil), then minus power was added to the correction –0.25 D at a time. The end point of accommodative amplitude was noted as the point at which patients lost one line of Snellen acuity. The second method was to refract the patient, administer pilocarpine to constrict the ciliary muscle and move the IOL forward, then refract the patient again. The difference between the two refractions represented the accommodative amplitude.

In the 10 eyes implanted with the second prototype of the IOL, the average accommodation at an average of 1.9 months postoperatively was 2.38 D. This increased to 2.80 D at an average of 11 months postoperatively. Five eyes reached an average follow-up of 25.8 months (range: 21 to 31 months). Accommodative amplitude as measured by the first method averaged 2.25 D (range: 1.75 to 2.75 D). Using the pilocarpine method, accommodation averaged 2.70 D (range: 2.00 to 3.50 D). A-scan measurements made after application of a mydriatic and then later after pilocarpine demonstrated in all eyes that there was anterior movement of the optic, including one eye in which Nd:YAG posterior capsulotomy had been performed.

Uncorrected visual acuity in all but one eye with macular disease was measured at 20/20 to 20/30 distance and near vision of N4 (equivalent to J4). No patient required spectacles. The average age of patients in the study was 83 years, which is a significant finding.

"The ciliary muscle is still working at that age," Kammann emphasized. "Presbyopia is a result of the increasing stiffness of the lens, not the failure of the muscle. If the ciliary muscle were responsible for presbyopia, it would be the only muscle in the body that ceases to function with age.

"We also observed that the ciliary muscle was working better the longer after surgery we examined the patient," Kammann added. "The ciliary muscle was in training."

New directions

Cumming believes that the experience with this lens points to an alternative explanation of IOL decentration.

"The reason that lenses decenter is not because of the pea-pod effect that some have theorized," he said. "What happens is that as patients look from distance to near, the ciliary muscle constricts and pushes the IOL loops toward the center of the bag. Then when the patient looks into the distance again, the loops move out. As capsular fibrosis advances, sometimes the loops move in one direction and then don't go back all the way, or one loop moves but the other does not. That's why plate-haptic lenses have less decentration than other lenses. They cannot be compressed."

Goals for the future of the accommodating IOL include refining the lens design — Cumming has already advanced to a fifth prototype — and developing strategies for restoring pre-presbyopic levels of accommodation.

"We're trying to achieve an even greater accommodation amplitude," Cumming explained, "because then you can aim for a lens power that is slightly on the plus side, about +0.5 D. This will allow the patient to have distance vision by accommodating for emmetropia and then by further accommodation allow for near vision, thus eliminating the need for glasses."

For Your Information:

J. Stuart Cumming, MD, is in private practice at Anaheim Eye Medical Group, Suite 201, 1211 West La Palma Ave., Anaheim, CA 92801; (714) 533-3126; fax (714) 533-9920. He is a paid consultant for Medevec and has a financial interest in the accommodating silicone IOL.

Jochen Kammann, MD, is head of the Department of Ophthalmology at the St. Johannes Hospital, Johannes Strasse 9-11, Dortmund 44137, Germany; (49) 231-18-43-22-41; fax: (49) 231-18-43-70.

Medevec BV is located at Koningslaan 34, 1075 AD Amsterdam, The Netherlands; (31) 20-664-44-61; fax (31) 664-77-47.