Intacs refractive effect can be easily ‘reversed’

After nearly 3 years of implantations, Intacs have now been shown to be removable, replaceable and safe.

Issue: September 1, 2000

BOSTON — Since Intacs micro-thin prescription inserts (KeraVision Inc., Fremont, Calif.) came out on the market, there have been claims and counterclaims regarding the accuracy of KeraVision’s marketing tag line of “the power to change your vision, the freedom to change your mind.”

At the annual American Society of Cataract and Refractive Surgery meeting here, several papers were presented that held the KeraVision claims to be true.

Michael Twa, OD, explained that the papers presented not only proved the stability and accuracy of the Intacs system, but also their reversibility.

In and out and in Intacs

A 51-year-old patient was entered into the original Food and Drug Administration (FDA) clinical study and had surgery in April 1997. He was presbyopic, which factored into his surgical technique. He was a mortgage broker who needed his near vision to see the contracts he was reading for work and he needed to drive around his county frequently on work-related business. So, functional near and far vision were very important. He also was an avid recreational pilot.

In his right eye, he was –2.75 D and was treated with a 0.35-mm Intacs. In his left eye, he was –2.5, monovision was surgically induced with a 0.25-mm Intacs to a –1 undercorrection. In 6 months, his right eye was plano and his left eye was –1.25.

About a year after implantation, he came back to his doctor. “Remember, he’s an avid pilot. Unfortunately, in the United States you cannot have an experimental device implanted in your eyes. His flight surgeon revoked his flight certificate. He called up in a fit, and said something had to be done. We took the Intacs out,” Dr. Twa said.

The removal procedure utilized a Sinskey hook to find the original lamellar dissection and then placed the tip of the Sinskey hook into the positioning hole of the Intacs and rotated it out of position. In the other eye, a second incision was necessary, but the remainder of the procedure was the same.

Three months after removal, his refractive results were within a 0.25 D of his refractive results preoperatively in his right eye and within 0.5 D in his left eye, and he was able to use his preoperative spectacles for refraction. The topography measurements all went back to preoperative levels.

“In April 1999, the FDA approved the Intacs, and 4 months later so did the Federal Aviation Administration. And the patient asked to have them put back in, so we gave him a new pair,” Dr. Twa said.

To implant the new Intacs, the existing incisions were opened and probed to find the same lamellar tunnels. At that point, Intacs were placed back in, and the patient was 20/20 again in the right eye for distance and reading 20/25 at near in the left eye. The topography was almost identical after both implantations. The Intacs produced a predictable result.

The reversibility of the Intacs procedure was further demonstrated by Hamza N. Khan, MD, who presented the results from 71 eyes that had Intacs implantation at the Gimbel Eye Centers between August 1998 and July 1999.

Nearly 34% of the eyes that received Intacs had removal procedures. These reasons included under-response in 20 eyes, over-response in two eyes, induced astigmatism in one eye and shallow placement in one eye.

Enhancements included removal and replacement and six removals followed by laser in situ keratomileusis. All eyes returned to within 0.25 of their original refraction within 2 to 12 weeks, with 4 weeks being the average.

Dr. Khan believes this preliminary data showed that Intacs placement is a reversible procedure.

Thomas E. Clinch, MD, based his results on all 449 of the subjects of the KeraVision United States FDA clinical trials. Removal occurred in 50 eyes including 41 initial eyes and nine contralateral eyes. Uncorrected visual acuity diminished in all eyes after explantation. No subjects lost greater than one line of best spectacle corrected visual acuity.

Dr. Clinch explained that many of the eyes that were explanted were done because originally 0.35 mm thickness Intacs were assumed to have a greater power curve, and patients were being undercorrected.

Originally, the Intacs were categorized for treatment as: 0.25 mm was 1 to 1.9 D; .30 mm was 2 to 2.9 D; and 0.35 mm was 3 to 3.9 D. Midway through the study, the ranges were changed to 0.7 D steps.

He concluded that the Intacs appear to be reversible. Following Intacs removal, 90% were within 0.5 D of their original refraction, and 76% were within 0.25 D of their original refraction.

Channel deposits are reversible

Along with the refractive reversibility, the lamellar channel deposits that tend to fill the spaces between the Intacs and the stroma also appear to be reversible, supported by a confocal specular microscopy study.

Terry E. Burris, MD, explained that the two major types of opacifications are channel haze and tunnel deposits. Channel haze is caused by the disruption of the transparent lamellar matrix by the dissector. This usually progresses to a grey translucent haze that occurs weeks after the procedure and is not a problem for refractive results.

Tunnel deposits are a space-filling phenomenon occurring weeks or months after implantation. They can range from clear gel-like deposits to fine spicule deposits to gray, chalky amorphous deposits that can become more confluent with time, and finally an uncommon crystal formation that infrequently occurs in thicker Intacs usually 1 year after implantation. The thick Intacs that Dr. Burris referenced are the 0.4-mm and 0.45-mm Intacs that are not yet available in the United States.

“The incidence of deposits increases with time and stabilizes in 1 to 2 years. The thicker the Intacs, the more prominent the deposits. The lamellar deposits are benign and of unknown origin. They may represent extracellular or cellular material. In some patients, they have resolved. They also resolve after Intacs removal 3 months to 1 year later,” Dr. Burris said.

In the case studies he presented, one patient showed amorphous deposits with slight crystallization in one eye that had the Intacs in for 18 months. His other eye showed no deposits and had been in 1 year longer. When the eye affected with deposits was looked at on month 32, there were very few deposits. He actually had some macrophage activity that appeared to be “devouring” the deposits that had formed in his eye.

Another patient had finer crystalline deposits that were very fine spicules. The deposits showed no bacterial elements. One of the deposits did look somewhat cellular, according to Dr. Burris, but may have been some epithelium that had made its way into the channel and begun to degenerate. The patient had some macrophage activity on the inside of the ring, with very few deposits.

Dr. Burris concluded that while Intacs may produce characteristic deposits that occur in the lamellar tunnels, they tend to reduce over time. One likely reason for this is that macrophages appear to “chew” the deposits up.

For Your Information:

Michael Twa, OD, can be reached at 9415 Campus Point Drive, Shiley Eye Center, La Jolla, CA 92093; (858) 822-1553; fax: (858) 822-1514. Dr. Twa has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

Hamza N. Khan, MD, can be reached at 11910 111th Ave., Ste. 140, Edmonton, Alberta, T6H 1W5, Canada; (403) 452-4111; fax: (403) 452-4114. Dr. Khan has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

Thomas E. Clinch, MD, can be reached at University Ophthalmic Consultants of Washington, 4910 Massachusetts Ave. NW, Ste. 210, Washington, DC 20016; (202) 686-6800; fax: (202) 686-6668. Dr. Clinch has no direct financial interest in any of the products mentioned in this article. However, he is a paid consultant for KeraVision.

Terry E. Burris, MD, can be reached at Northwest Corneal Services, 6950 S.W. Hampton, Ste. 150, Portland, OR 97223; (503) 624-4814; fax: (503) 624-4904. Dr. Burris has no direct financial interest in any of the products mentioned in this article. However, he is a paid consultant for KeraVision.

KeraVision Inc. can be reached at 48630 Milmont Drive, Fremont, CA 94538; (510) 353-3000; fax: (510) 353-3030.