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More than 2,000 CrystaLens IOLs implanted worldwide
The developer of the lens recalls its history, and the surgeons who implanted the 1,000th and 2,000th lenses discuss their results.
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C&C Vision’s accommodative IOL, the CrystaLens, has been implanted in more than 2,000 eyes worldwide. But unknown to most people is the history of the lens and the man who designed it, the long story of an idea that fought its way through many obstacles but finally seems to be gaining success.
In 1989, J. Stuart Cumming, MD, first had the intuition that a lens that moves back and forth in the eye might be feasible.
“I was implanting the plate lens from STAAR Surgical at the time, and I noticed that some of my patients could see well both at distance and at near,” Dr. Cumming said. “Even behind the phoropter some of them could read J1 with distance correction. I took 10 of these patients, A-scanned them, first with cycloplegic drops and then with pilocarpine, and found that the optic was moving forward about 0.7 mm. It was then I realized the ciliary muscle must still be functioning in these older patients. Although in the literature they were saying the ciliary muscle becomes atrophic with age, it was the only thing that could be moving these lenses.”
Other observations followed, which made Dr. Cumming consider that the vitreous must be somehow involved in this process of “pseudo-accommodation.”
“I found that plate lenses had a tendency to place themselves more posteriorly compared to loop lenses, and they leaned against the vitreous all the time. It might therefore be some movements of the vitreous that push the lens forward in concomitance with constriction movements of the ciliary muscle,” he said.
Vitreous pressure
Dr. Cumming found a paper published in 1955 by an Italian ophthalmologist living in São Paulo, Brazil. He was an anatomic artist who had drawn what he saw through a gonioprism in the eye of a young patient with aniridia, first under the effect of pilocarpine and then of a cycloplegic.
“Since there was no iris, he could see the ciliary muscle, the zonules and the lens. Once he had finished these drawings, he reduced them to a grid to see how the ciliary muscle changes place and what happens to the shape and position of lens and zonules,” Dr. Cumming said.
“When I looked at these drawings, two things were apparent. First, the insertions of the zonules move forward with constriction of the ciliary muscle. Second, the ciliary muscle, like every muscle in the body, changes shape with constriction, and it changes in such a way that it vaults backward into the vitreous cavity. So I understood that the vitreous cavity would increase in pressure with constriction of the ciliary muscle, and this was moving the lens optic forward.”
A paper by Jackson Coleman, MD, published in 1986, confirmed this finding.
“He canalized the anterior chamber and vitreous cavity in 10 primates, stimulated the ciliary muscle and found there was a simultaneous drop in pressure in the anterior chamber and increase in pressure in the vitreous cavity,” Dr. Cumming said.
The premises to design an IOL that relied on these natural dynamics of the eye for reproducing the movements of accommodation were all in place.
“It occurred to me I could design a lens that would vault backward and be up against the vitreous face, and if this cavity increases in pressure with constriction of the ciliary muscle, it may move forward and be an accommodating lens,” he said.
Ciliary muscle remains young
The idea relied on the supposition, not yet proven, that the ciliary muscle maintains its functional capability throughout life.
“It’s only recently that Susan Strenk demonstrated by high-resolution MRI studies that at all ages the ciliary muscle maintains its contractility. She said the ciliary muscle becomes stronger with time. Back when I was doing my research, this was not at all taken for granted, but I bet on it and won,” Dr. Cumming said.
The real cause of presbyopia is not in the muscle but in the ectodermal structure of the lens, which produces new cells throughout life, Dr. Cumming said. As the lens grows larger and the distance between it and the ciliary muscle becomes smaller, the zonules become floppy, and this is why patients lose accommodation, he explained. The ciliary muscle is constantly trying to change the shape of the lens, but is not successful because the zonules are not tight.
“The trick was to try to design a lens that would function all the time, maintaining the elasticity and tension that the natural structures of the eye lose with age. I started from the plate lens and thought if we made the plate longer, there would be more mechanical advantage, and the optic would move back and forth more easily. So I reduced the size of the optic to 4.5 mm and designed two grooves across the plate to enhance elasticity,” Dr. Cumming said.
To prevent the lens from dislocating once implanted in the capsular bag, the ciliary muscle was to be paralyzed for a few days with atropine until the plate had become well embedded into the capsule.
The first patient, an 85-year-old woman, was implanted in England in March 1991.
“When I examined her that July, she was accommodating 4 D to 5 D. This was my ‘eureka’.” Dr. Cumming remembered. “I A-scanned her first with pilocarpine and then without it, and you could see there was a decrease in the anterior chamber depth of 2.5 mm and an increase in vitreous cavity length of 2.5 mm. One millimeter was approximately 2 D of accommodation. That was really an exciting day. I remember driving over the hill from the hospital to my parents’ home in England, singing at the top of my voice, ‘This is it, it really works.’ On that day I realized we could make an accommodating lens. Little did I realize it was going to take 10 years.”
Failed attempts, final success
During the next 9 years, Dr. Cumming collaborated with Joachim Kammann, MD, in Germany, implanting several designs of the lens.
“The first six designs all accommodated, but invariably after 2 to 3 months they would slip out of the capsular bag into the sulcus,” he said. “Obviously, these designs were all unacceptable, and it was disheartening because once you knew there was a complication we had to make a new mold, make the lenses in different powers, sterilize, package them, implant them and follow the patient. Each lens design took more than a year.”
Rewarding results
The IOL’s final design, the Crysta-Lens, is made of third-generation silicone (Biosil) with polyamide loops.
“All previous designs had flimsy silicone loops that slipped out of the bag. The special thing about the new loops is that they get trapped between the anterior and posterior capsules, and the two knobs on the end prevent them from slipping away. The capsule fuses over them through natural fibrotic processes and holds them firmly in the bag,” Dr. Cumming explained.
The total length of the CrystaLens is 10.5 mm, the same as a standard lens. The optic diameter is still 4.5 mm.
“Results are extremely rewarding,” he said. “The first patients, who were implanted in Mexico, now have more than 3 years of follow-up and can see well at distance and near. None of them use glasses. The first results of the Food and Drug Administration trial on more than 400 cases also show that 94% of bilaterally implanted patients have uncorrected visual acuity of 20/25 or better, 98% read J1 at intermediate and 59% J1 at near. All patients are at least 20/40 and read J3. About 95% don’t wear glasses.”
1,000th lens implanted
Erik L. Mertens, MD, who implanted the 1,000th CrystaLens last year, is also satisfied with his results.
“Of my 17 bilaterally implanted patients, 15 (90%) have UCVA 20/25 or better and read J1 or better, and 100% are 20/40 or better and read J3,” he said.
He offers the option of CrystaLens implantation to patients who are 50 years or older, with less than 1 D of corneal cylinder and the ability to achieve best corrected visual acuity of 20/30.
“I treated eyes with more than 1 D of astigmatism, but performed limbal relaxing incision in those cases,” he said.
Preoperatively, immersion biometry is mandatory to obtain reliable measurements of the axial length, he recommended. Applanation biometry flattens the cornea and leads to inaccurate results, which are particularly detrimental with this type of lens.
The surgical technique requires no special variations compared to standard phaco.
“Implantation is done through the phaco incision, enlarged to 3.5 mm. The only variations are the instillation of atropine at the end of surgery and the size of the capsulorrhexis,” he said.
“At the beginning, I performed a smaller capsulorrhexis, thinking this would prevent the lens from shifting forward and dislocating. Then I realized that a small capsulorrhexis, when the capsule shrank, would sometimes create the effect of a buttonhole, pushing itself behind the optic of the lens and trapping it there. After the first few eyes, I started performing a larger capsulorrhexis, between 5 mm and 6 mm, which cannot possibly make the capsule get trapped behind the 4.5-mm optic of the lens.”
Accommodation will not cease
Dr. Mertens has no doubts that the lens will continue working in the long term as it does now.
“There’s no reason to believe that accommodation will not be a lifelong bonus of this lens,” he said. “Silicone is a soft and flexible material that maintains its characteristics even after years. Therefore, the lens will always be able to move back and forth in the eye.”
He thinks fibrosis of the capsule will not be a problem either.
“It has been demonstrated that YAG laser capsulotomy doesn’t hinder the accommodative process, but makes it even better. I YAGed both eyes of my first patient, but this didn’t hinder her reading capability,” he said.
He noted that in this patient the fibrotic process was triggered by the small capsulorrhexis.
“The anterior capsule got trapped under the lens and I had to YAG both the anterior and the posterior capsule, which had fused together. When you do a larger capsulorrhexis, there is not such a problem; there’s always space between the anterior capsule and the posterior capsule, and the lens moves freely between them,” he said.
2,000th lens implanted
The 2,000th CrystaLens was implanted by Lucio Buratto, MD, who has used this lens in 40 eyes of 32 patients aged 34 to 87 years.
“Our results are very satisfactory. There are 29 patients (92%) who can now read J1 to J3 with distance correction, while three patients can read between J5 and J6. Of these three, two have developed posterior capsular opacification and are now waiting for YAG capsulotomy, and in one the low performance of the ciliary muscle was due to years of glaucoma therapy with pilocarpine,” he said.
The potential excursion of the lens during accommodation was evaluated in each patient by measuring the anterior chamber depth after instillation of pilocarpine, which causes contraction of the ciliary muscle.
“The mean variation of the anterior chamber depth was 1.3 mm,” Dr. Buratto said.
Fogging technique was then applied to all patients to measure the range of postop accommodation, which was 2.1 D on average.
During surgery, Dr. Buratto uses a bimanual technique for irrigation-aspiration of material from the back of the lens and special forceps (Janach) to implant the IOL through a 3.2-mm incision.
“We are still evaluating the size of the capsulorrhexis for this lens, but I like a rhexis a little larger than the optic disc,” he said.
Apart from the two cases of PCO, no complications were reported.
“A small minority of patients complained of halos and night glare, which disappeared a few days after surgery,” he said. “Although the optic of the lens is very small, glare and halos are not a problem because the lens is positioned very posteriorly toward the retina and the beam of light has a smaller diameter there.
“Moreover, atropine, instilled at the end of surgery to paralyze the ciliary muscle while the fibrotic processes fix the loops to the capsule, allows a perfect centration of the lens. Centration is optimal in the postoperative time, and in the long term the lens remains well-centrated.”
Retraining near vision
Both surgeons stressed the importance of reading without spectacles right from the early postop period.
“We must make our patients aware that they have to train near vision after this IOL has been implanted,” Dr. Mertens said. “At age 70, the ciliary muscle hasn’t been working for 25 years, and has to be retrained to do so. Patients who were using reading glasses after surgery were never able to read well. Others, who made the effort to use near vision without spectacles, reported better vision after a time variable between 2 and 5 months.”
Dr. Buratto said most patients are showing a high degree of satisfaction with this lens, and an increasing number of potential candidates are choosing this option despite the higher costs involved.
Dr. Mertens said that 8% of his cataract patients want to have this IOL implanted.
“They must be able to afford the entire cost of the lens, which is not reimbursed by insurance like a normal IOL. To eligible candidates, I offer this option and let them choose,” he said.
For Your Information:
- J. Stuart Cumming, MD, is Chief Scientific Officer of C&C Vision. He can be reached at 6 Journey, Suite 270, Aliso Viejo, CA 92656; (949) 916-9352; fax: (949) 716-8362. Dr. Cumming has a direct financial interest in the CrystaLen. He is the chief scientific officer for C&C Vision.
- Erik L. Mertens, MD, can be reached at Kapelstraat 8, B2660 Hoboken, Belgium; (32) 3-828-2949; fax: (32) 3-820-8891; e-mail: e.mertens@skynet.be. Dr. Mertens has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
- Lucio Buratto, MD, can be reached at Piazza della Republica 21, 20124 Milan, Italy; (39) 02-636-1191; fax: (39) 02-659-8875; e-mail: office@buratto.com. Dr. Buratto has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.