07/18/2005

Anterior Chamber, Iris-Fixated Lens Advantages Highlighted

The advantages of anterior chamber IOLs are many and compelling, according to one surgeon who uses them after he previously doubted them.

Vance M. Thompson, M.D., associate professor of ophthalmology, University of South Dakota School of Medicine, Sioux Falls, S.D., plans to discuss the devices at the 2004 annual meeting of the American Academy of Ophthalmology, New Orleans. His presentation is titled “Point-counterpoint: Anterior chamber phakic IOLs.”

Dr. Thompson said the advantages of the anterior chamber iris-fixated lens include a more than 20-year track record for safety; the safety of its location in the eye; its adaptability to different pupil positions; and because it is located at a safe distance from crystalline lens and the cornea Dr. Thompson — a former LASIK and PRK investigator — reached these conclusions only after a long period of distrust of the anterior chamber lens.

“I came to the conclusion that I really liked the iris-fixated, but that was only after getting over the hump of thinking about previous iris implants and realizing that their main problem was because they had haptics that were both against the anterior iris and the posterior iris,” Dr. Thompson said.

He concluded previous iris clip lenses were not actually fixated, but rather they simply placed haptics on either side of the iris that could move and the haptics would rub against the iris as the pupil got bigger and smaller. The posterior haptics rubbing against uveal tissue led to inflammation and eventually corneal decomposition in many of cases.

Dr. Thompson said the Artisan/Verisyse lens (Ophtec USA, Boca Raton, Fla.), now under FDA review, appealed to him because it pinches the anterior iris tissue, and specifically the iris stroma. The clinical literature has shown it does not disrupt iris vasculature, and iris angiography is normal afterward. Studies also have not found chronic cell and flare with the lens.

The Verisyse lens also provides a safe distance between the implant, the crystalline lens, and the corneal endothelium as seen through Scheimpflug photography. Dr. Thompson said the vault of posterior chamber implants also is supposed to keep a safe distancefrom the crystalline lens but that varies from person to person. Since the posterior chamber it is in such a sensitive space, only time will answer whether it lives up to that potential.

An additional advantage for Dr. Thompson, who has implanted more than 150 of the lenses over seven years, is that the design does not place foreign material in the angle. Angle-fixated lenses have the drawback of requiring very accurate measurements of the diameter of the anterior chamber or the diameter of the ciliary sulcus.

“Those are two very difficult measurements,” Dr. Thompson said. “And with the Verisyse, it doesn’t matter what the diameter of the ciliary sulcus or the anterior chamber is. You just place it over the pupil and fixate.”

The final key point for Dr. Thompson is the lens’ ability to accommodate the many patients that do not have a pupil directly in the center of their iris. The haptics in both the anterior chamber angle supported and posterior chamber ciliary sulcus-supported lenses do not account for varying locations of the pupil. But the Artisan/Verisyse implant is designed to center directly over the pupil.

As a long-time refractive surgeon, Dr. Thompson said other surgeons need to be vigilant to avoid thinning the cornea too much with LASIK and that phakic implants offer a great option to these patients.

He does not perform LASIK without at least 500 microns of corneal thickness, even if it is a small correction.

In patients with thin corneas that need low corrections, PRK is his first choice but when patients get to about 3 D, “I start thinking of phakic implants,” he said.

An important point for surgeons that may consider refractive IOLs is proper patient education and preparation. All patients that consider the implant should be informed they need a minimal anterior chamber depth of at least 3.2 mm, which is what it was in the clinical trial.

“So if it is someone with a shallow anterior chamber depth, this is not a good option,” Dr. Thompson said. Patient endothelial cell counts of at least 2,000 are critical before committing to surgery also.

“So patients need to understand that these measurements of anterior chamber depth and endothelial cell counts need to happen before they are told they are a good candidate.”
Post-operatively, some patients require enhancements — such as laser enhancements or astigmatic keratotomy. It is important for surgeons to manage expectations, because they will address very high levels of correction.
“It is wonderfully exciting technology, but if they are going for the best possible uncorrected vision, they may need other refractive modalities to enhance,” he said.

Dr. Thompson said surgeons should avoid the technology on patients with anterior segment abnormalities, iris abnormalities, cataracts or corneal endothelial problems, irregular astigmatism, iritis, or glaucoma.

Editors’ note: Thompson has no financial interest in Ophtec.

Rich Daly EyeWorld Staff Writer