Intacs implantation takes no more time than LASIK

August 15, 1999

Laser in situ keratomileusis (LASIK), though highly effective, really was designed for moderate to high myopia and to correct astigmatism. If one goes back just 2 years ago, few surgeons were routinely performing LASIK for patients with 1 D and 2 D of myopia. Only recently have more surgeons become comfortable enough with LASIK that they have worked down into the low levels of myopia. However, now there is an alternative to LASIK for patients with low myopia.

KeraVision Inc.’s (Fremont, Calif.) Intacs intrastromal corneal ring segments are specifically designed for low-level myopia. Patients like the idea that this procedure has been designed and tested specifically for them. Surgeons like the procedure because it is easily reversible and takes no more time than LASIK.

Patient selection

Patient selection for Intacs segments is fairly well defined by the Food and Drug Administration (FDA). Candidates for this procedure should have between 1 D and 3 D of myopia and 1 D or less of astigmatism. I prefer patients with 2.75 D or less of myopia, and with astigmatism of 0.75 D or less. I prefer this because the next thicker ring size has not been approved by the FDA, and one of the things that patients like about this procedure is its ability to be removed or exchanged. If you have a patient who is undercorrected, you currently do not have the thicker ring size available for enhancement. For this reason, I prefer patients who have slightly less myopia than the amount for which the Intacs is approved.

We have learned in the clinical trials that the procedure does not correct astigmatism. Also, we have learned from our excimer patients that someone with 1 D of astigmatism is not going to be happy postoperatively. So if patients have significant cylinder, I perform LASIK rather than implant Intacs segments.

Preparation

Intacs surgery is similar to LASIK in the sense that it is an outpatient, topical procedure that takes about 5 minutes to perform. Because it takes little time, it does not interfere with my normal surgical schedule. I can do LASIK, then an Intacs implant and then another LASIK.

The topical anesthetic that I use is tetracaine (Cetacaine; Cetylite). Patients receive one drop before the preparation and one drop before the procedure. The prep and drape are important because you need to isolate all of the lashes to make sure that the Intacs device does not touch any of the lashes or bring any bacteria into the channel. So I use a slit, 3M 1020 drape and a wire lid speculum — the same format I use for LASIK (Figure 1).

The antiseptic prep is a little bit more aggressive than LASIK, again, to make sure there is no implantation of bacteria. I use Betadine (povidone iodine; Purdue Frederick) paint on the eyelids, but I also place 2% povidone iodine solution into the cul-de-sac for 1 to 2 minutes and then wash it out prior to the procedure.

Implantation in three steps

The actual implantation procedure involves making an incision, a channel and then implanting the ring.

The incision step is the most important. There is a special KeraVision marker (Figure 2) that is placed around the geometric center of the cornea. The incision location should be 8 mm from the geometric center of the eye.

It is important to be in the geometric center of the cornea rather than the center of the pupil. The implant works by separating the corneal fibers in the periphery and needs to be equally spaced from the limbus. Many of us are used to putting refractive surgical procedures on the pupil, so this is a change. The incision marker will make a 1.8 mm mark. The actual incision is made with a diamond blade to two-thirds of the depth of the corneal thickness at the location of the incision, which needs to be measured intraoperatively (Figure 3).

After the 1.8 mm, a two-thirds depth of an incision is made, and a Sinskey hook is used to make a pocket going sideways at the bottom of the incision at the 12-o’clock position.

I prefer to grasp the edge of the wound with the forceps and look through the bottom of the incision when I am starting the pocket with the Sinskey hook. I do this to make sure that it is at the bottom of the incision and is equal on both sides (Figure 4).

Then the pocket is extended with a stromal spreader, which allows you to have a 1.8 mm wide channel, 2 mm in length and extending clockwise and counterclockwise from the original incision (Figure 5). This is the most important part of the procedure. You must start the channels at an equal level on either side and at two-thirds depth.

Steps 2 and 3

The second step of the implantation procedure entails creating the channels in the stroma in a clockwise and counterclockwise direction. This is done by placing a special suction ring, made by KeraVision, on the cornea and centering it (Figure 6).

The suction ring has a centering de vice and is well designed. It does not slip or slide and maintains a good grip on the eye.

After suction is released, we begin the third stage of the procedure, which is the easiest. In this step, the Intacs segments are placed into the channel (Figures 7a, 7b and 7c). There is a clockwise and counterclockwise ring. Each ring is designated as such in the packaging so that you know in which direction to go. Those are placed in the channel with a twisting or dialing motion.

Closing

There is still a debate over whether the incision should be closed with a suture — as we did in the clinical trials — or left open. Physicians with minimal Intacs experience should suture the incision with a single, 11-0 nylon suture (Figures 8a and 8b). This is to approximate the anterior leaflets of the incision. Suturing should be continued until you are completely comfortable with the procedure.

Currently, I am involved in a randomized, prospective study comparing sutured with non-sutured Intacs eyes. In Canada and Europe, when the physicians stopped using sutures, outcomes suffered; however, we are not sure why. I suspect that the incision communicates with the channel during healing. If the wound is even open slightly during the first 1 to 2 weeks postop, tears can enter the channel and could cause variability in wound healing or some variation in vision throughout the day.

One of the drawbacks to the suture is that if you tie it too tightly, you will induce astigmatism. Sutures should be re moved approximately 1 month after surgery.

Outcomes

During our clinical trial, in which there were 410 eyes of 410 patients, 60% achieved uncorrected visual acuity of 20/20 at 1 month, and 74% were seeing 20/20 or better uncorrected at 1 year. Fifty-three percent of the patients were 20/16 or better. It should be noted that the percentage of patients in the clinical trials who saw 20/20 was higher than the clinical trial data on photorefractive keratectomy or LASIK for comparable levels of myopia.

About 10% of the refractive surgery patients I am treating are having Intacs implanted. Because the potential population for Intacs is very large, we are starting to see an increase in the number of low spherical myopes who are coming into our practice for surgery.

Word is getting out among patients that there is a procedure specifically designed for low myopia. My average Intacs patients — they are usually in their 30s — are younger than my average refractive surgery patients, who on average are 43. As a result of this new device, I am seeing a younger group who likes the idea of obtaining high-quality vision in a simple outpatient setting.

For Your Information:

• Daniel S. Durrie, MD, can be reached at the Eye Center of Kansas City, 5520 College Blvd., Overland Park, KS 66211; (913) 491-3737; fax: (913) 491-9650; e-mail: ddurrie@novamed.com. Dr. Durrie has no direct financial interest in any of the products mentioned in this article. He is a paid consultant for KeraVision.

• For more information on Intacs intrastromal corneal ring segments, contact KeraVision Inc. at 48630 Milmont Drive, Fremont, CA 94538-7353; (510) 353-3000; fax: (510) 353-3030; Web site: www.keravision.com.