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PermaVision corneal implants show good results in phase 2 trials
Researchers find that design and technique improvements have reduced or eliminated the implant's earlier problems of decentration and glare.
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The PermaVision corneal implant has completed enrollment in phase 2 U.S. clinical trials and the patients are being followed to support initiation of phase 3 trials, according to manufacturer Anamed. The company has instituted changes in the lens design and delivery system that have largely eliminated the unsatisfactory results of the first-generation implants, researchers said.
"A lot has changed since it was introduced in Europe some years ago. Actually, everything has changed: the lens design, the drug regimen, the way we are putting it in," said Stephen G. Slade, MD, FACS, of the Slade & Baker Vision Center in Houston.
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Dr. Slade's center was one of 10 clinical sites that participated in the phase 2 trials for Food and Drug Administration premarket approval of the implant.
With a refractive index of 1.376, the PermaVision implant can be used for the treatment of either hyperopia or presbyopia. Researchers have recently focused on its use in presbyopic patients.
Herbert E. Kaufman, MD, the medical monitor of the FDA trial of the lens, said in a presentation last year that changes to the PermaVision were made in response to European clinical experience. He said the changes include the use of a power wash to reduce corneal flap interface debris and a change from a stainless steel cage system to hold the lens to a titanium spoon holding system, which eliminates potential ferric oxide ions in the storage solution from the stainless steel.
Dr. Slade added that the two most important changes to the PermaVision implants and surgical technique are reduced edge thickness and a change in the drug regimen.
"The drug regimen has changed in that we have learned how to best use steroids before surgery, during surgery and after surgery," Dr. Slade said.
According to Dr. Slade, practitioners are now administering Pred Forte (prednisolone acetate ophthalmic suspension 1%, Allergan) 1 hour before surgery to "pre-load" the eye. The preoperative loading along with postoperative use has eliminated haze problems that arose in earlier trials, he said.
The edge thickness of the lens has been reduced from 20 µm to less than 10 µm, allowing the corneal flap to conform precisely around the edge of the implant, Dr. Slade said.
"Ten microns is fantastically thin. We really can't get much thinner than that," he said.
Rounding out the improvements to the surgical technique is the use of the IntraLase FS laser to create customized flaps, which improve centration.
According to Dr. Slade, researchers have designed and written software for customized flaps that have specific recesses or depressions, allowing the 5-mm lens to fit precisely without decentration. The lenses have even been injected into the stroma in channels created by the IntraLase laser within the cornea, he said.
Clinical summary
At the American Academy of Ophthalmology meeting, Dr. Kaufman delivered a clinical summary of the phase 2 results in 98 eyes implanted with the updated model of the PermaVision lens using the improved surgical procedures.
Of the 98 eyes implanted with the lens, 4% demonstrated mild haze affecting refraction.
Four cases of clinically significant decentration were reported, resulting in the explantation of those four lenses.
After 6 months, 87% achieved an uncorrected visual acuity of 20/40 or better, Dr. Kaufman said.
He noted that if a patient finds the implant to be unsatisfactory, it can be explanted without any tissue removal, and if the eye's refraction changes over time, the implant can be exchanged.
"I am really excited about it because it is so easily removable," Dr. Slade said.
Initial design
The first-generation PermaVision corneal implants were associated with a high incidence of halo and glare in early clinical trials, according to Michael C. Knorz, MD, who presented the clinical results with the earlier design and implantation technique at last year's AAO meeting.
Dr. Knorz explained that as a result of the less-than-satisfactory results with the first-generation intracorneal lens, manufacturer Anamed instituted changes in the lens design and delivery system in an effort to improve future results.
He reported on the results of first-generation PermaVision lenses implanted in 21 eyes with a mean preoperative refraction of +3.6 D. The lenses were implanted between December 2000 and October 2002.
The researchers observed a haze around the implants in 86% of the eyes, and a large percentage of patients reported halos and glare. Of 21 implants in 12 patients with up to 4 years follow-up, one-third of the lenses were explanted due to the unwanted visual symptoms, Dr. Knorz said.
Other complications included decentration of more than 1 mm in four eyes, mild to moderate corneal haze beginning 3 to 6 months postoperatively around the edge of the implant in 18 of the 21 eyes, and severe halos and disabling glare in eight eyes.
Dr. Knorz explained that the halos and glare were the result of a small optical zone and forward light scatter due to encapsulation of the stromal implant.
"Further studies are needed to establish the long-term complications of intracorneal lenses," Dr. Knorz said at the AAO meeting.
PermaVision background
The PermaVision implant is composed of Anamed's microporous hydrogel called Nutrapore, designed to mimic the properties of the stroma. The material is 78% water, similar to the cornea, and is highly permeable to water, oxygen and glucose, according to the company. Its refractive index is 1.37, close to that of the cornea.
The earliest designs of intracorneal lenses were made from glass or PMMA and were not tolerated well by the cornea, according to Dr. Knorz. Then came designs featuring multiple openings for the passage of nutrients, but corneal problems still occurred, he said.
The development of the highly permeable Nutrapore material, along with the presence of modern microkeratomes, triggered the rebirth of intracorneal lenses, he said.
The lens can be implanted in a sutureless surgical procedure similar to LASIK. A corneal flap is created, and the lens is placed under the flap and centered over the pupil. The flap is then folded back over the lens.
"Corneal implants are more appealing to doctors and patients [than phakic IOLs], as the surgery is much easier — just a flap, as in LASIK, no intraocular procedure," Dr. Knorz said.
The PermaVision lens received the CE Mark in 2001 and is currently available in Western Europe, the Middle East and South Africa. It is still investigational in the United States.
In 2003, the FDA approved expansion of clinical trials of the lens, and the U.S. National Institutes of Health awarded Anamed a $1.44 million phase 2 small business innovative research grant to help fund its U.S. clinical trials.
Since the completion of enrollment in the phase 2 study last year, Anamed was able to raise $12 million in venture capital funds for the upcoming phase 3 trials, according to Dr. Slade.
For Your Information:
- Stephen G. Slade, MD, FACS, can be reached at The Laser Center, 3900 Essex Lane., Suite. 101, Houston, TX 77027; 713-626-5544; fax: 713-626-7744; e-mail: sgs@visiontexas.com. Dr. Slade is a paid consultant to Anamed.
- Michael C. Knorz, MD, can be reached at Klinikum Mannheim, Theodor Kutzer Ufer 1-3, 68167, Mannheim, Germany; 49-621-383-3410; fax: 49-621-383-1984; e-mail: Knorz@eyes.de. Dr. Knorz has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
- Jared Schultz is an OSN Staff Writer who covers all aspects of ophthalmology. He focuses geographically on Europe and the Asia-Pacific region.