Refractive Surgery Edited by Arturo Chayet, MD

A Look Through the PermaVision Lens

Walter Bethke
Senior Editor

Though the technology is still young, it's showing the potential for treating hyperopia.

JUST WHEN SURGEONS THOUGHT THE cornea couldn't be heated, cut or ablated any differently to correct hyperopia, along comes the international clinical trial for the PermaVision lens (Anamed, Lake Forest, Calif.), which is implanted beneath a LASIK-style flap. This month's column will look at the latest data on this new implant, how the lens is being improved and how well it's working.

 

PermaVision’s delivery device helps prevent inverting the lens.

The Lens and the Theory Behind It

The PermaVision lens is a disciform piece of material called Nutrapore (a hydrogel material that's 78 percent water) that's 5.0- to 5.5-mm wide and 30- to 60-µm thick in the center. The lens's specification sheet states that Nutrapore's composition confers upon it the same refractive index as the human cornea. The lens's maker, Anamed, also says that there's been no corneal toxicity related to the lens in any of its animal or human studies, the latter of which are as advanced as one year postop.

The idea behind using the lens to treat hyperopia is simple: By inserting it beneath a LASIK flap, then laying the flap back down, the surgeon will have increased the relative steepness of the central cornea, changing the refraction in the minus direction and decreasing the hyperopia.

The PermaVision Lens: Adverse Events and Complications

The following data from 68 eyes were presented at the 2001 ASCRS Meeting:

One explant secondary to persistent decentration Exchanges: One planned exchange to prove replaceability Three secondary to improper correction One secondary to damaged lens at the time of surgery with induced irregular astigmatism No epithelial ingrowth or flap melt Mild central haze in one eye that resolved at nine months after six months of Pred Forte (Allergan, Irvine, Calif.) treatment Clinically insignificant haze at the border in five eyes One case of granular deposits that didn't affect vision at six months One case of keratitis that resolved with antibiotic and steroid treatment Twelve implants decentered by less than 1 mm Six didn't require intervention Five had to be recentered One required explantation Data courtesy Mitchell Shultz, MD

The Procedure

The initial steps of the procedure are devoted to preparing the lens. PermaVision investigators say the steps can be challenging, due to the lens's transparency and the design of the containment and delivery mechanisms.

"The delivery mechanism is the modality that the company is modifying," says Mitchell Shultz, MD, a U.S. investigator who will begin implanting the lens in his first human patients in October. He has reviewed the company's data thus far. "Originally, the lens came in a vial, and you had to fish it out," he says. "There was a lot of room for error." If it fell into the vial, the protocol recommended not using it, because the orientation may be wrong after the surgeon got it out. Fishing the lens out of the vial might damage it, as well.

Alok Nigam, PhD, CEO of Anamed, says his company has hit upon a delivery system that seems to solve the problems encountered with original methods.

"Before it was one spoon with a cage," he says. "Now it's two spoons sealed on the periphery with 500-µm clearance between them so the lens can't get out or turn over." He says the lens will be visible on one spoon or the other, so the doctor "doesn't have to make a decision as to whether the lens is in the correct orientation."

During the procedure, only when the lens is out and on a spoon is the patient brought in.

The surgeon uses a microkeratome to create an 8.5-mm flap. Sheraz Daya, MD, a British researcher who's implanted the lens in five eyes, thinks a larger flap would be better. "I think decentrations may have a lot to do with the size of the flap," he says. "It makes sense to have a large flap with more corneal tissue in touch with other corneal tissue. With a large lens under a flap with little cornea-to-cornea contact, it's conceivable there will be a chance of the lens's moving."

Once the flap is cut, managing corneal hydration becomes key. Dr. Daya makes the flap cut, irrigates the area, opens the flap, dries the bed and puts on the lens. With the delivery system he uses, the lens is applied by turning over the spoon on which it's sitting and placing it on the bed. The surgeon then touches the lens with a cannula through a hole on the spoon, and squeezes on a drop of BSS. Next, he lifts up the spoon but holds the cannula in place. This counterforce from the tip of the cannula displaces the lens from the spoon.

He waits 3 minutes for the lens to adhere before replacing the flap.

The Results

In the 60 patients in the international study, the average manifest spherical equivalent refraction was +3.52 D. For the 14 patients at the six-month follow-up point, it was +0.58 D.

Immediately postop, the patients are about ­0.5 D myopic. They drift toward plano over two to three weeks. Ironically, the first thing the patients notice, and which clues Dr. Daya in to the fact that the lens is having an effect, is not an improvement in their distance vision. Rather, they notice a deterioration in their near vision, even though their distance vision is improving simultaneously.

After the surgery, three of Dr. Daya's four patients are plano, and one is myopic. The myopic patient only had one eye done, however, and Dr. Daya believes she is accommodating with the untreated eye and the treated eye is a little myopic as a result.

The lens's effect goes beyond its 5-mm diameter, as well. On topography, it changes the corneal curvature out to 7-8 mm. The investigators tried a larger lens (6 mm), but the number of decentrations was higher with it, so the 5-mm size has become the lens of choice.

"It actually changes the shape of the anterior cornea," says Dr. Daya, "which is then reflected outward from the center."

Dr. Daya encountered two decentered lenses, one of which he removed after three months. After removal, the patient's vision took a month to stabilize, returning to his preop refraction. The other decentration was a +3.5-D lens that shifted in the first week. Dr. Daya says that the patient wasn't bothered by it, but he was.

"I suppose surgeons have an 'IOL mentality' that says a decentered lens affects vision," says Dr. Daya. "I think the lens creates such a broad corneal steepening, however, that it doesn't adversely affect vision. The patient sees 20/25 and J1 at near."

Interestingly, in the decentered patient's "better" treated eye, she sees 20/20 but only J3. Dr. Daya thinks the lens' inferior decentration helped the patient's reading vision.

So far, there haven't been any ectasia problems. Dr. Nigam says this is probably because, "we're not taking tissue out."

Dr. Nigam says there hasn't been any "remarkable" irregular astigmatism, but acknowledges that the number of patients and length of follow-up aren't that large or lengthy, respectively. "We'll need a bigger database to study that," he says.

Two patients in the 75 total eyes have increased light sensitivity, but there haven't been any subjective complaints of glare from the lens.

Currently, the lens has the CE mark in Europe, and Dr. Nigam expects to begin marketing it there in the middle of next year.