Surgeon: enhancements with the Intacs are ‘easy’

September 15, 1999

Editor’s note: This is the third and final part of a series of articles on experiences with the KeraVision Intacs. In this article, Daniel S. Durrie, MD, discusses photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) in eyes following Intacs explantation and Intacs implantation post-LASIK to correct residual error in patients that are not good candidates for repeat LASIK or PRK.

When I was asked to write an article on visual enhancements following implantation of KeraVision Inc.’s (Fremont, Calif.) Intacs intrastromal corneal ring segments, I knew it would be an easy task, because enhancements with Intacs are so easy to perform.

It is important to note that there should be little cause to surgically enhance the vision of a patient who has received an Intacs implant because patient selection should automatically rule out anyone with significant astigmatism. Intacs does not correct astigmatism, and after surgery, astigmatism cannot be corrected in an Intacs eye.

If a myopic or hyperopic touch-up is required, Intacs enhancements are extremely easy to perform. To enhance an Intacs eye, there are basically three options: the Intacs segments can be removed completely and the patient returned to his or her preoperative vision, relying on spectacle or contact lens correction; thicker ring segments, which would correct more nearsightedness, can be implanted and, likewise, thinner ring segments, which would correct less nearsightedness, also could be implanted. A third option is explantation followed by corneal refractive surgery. Corneal refractive procedures cannot be performed with an Intacs segment in place but are possible if ring segments are removed.

Patient selection

If patient selection is done properly, there should be little need for enhancement. The success of the procedure comes down to looking at if it will work in a given patient or not. If it does not work, take it out and either perform a LASIK procedure, or put the patient visually back to where they were before. If their ring is not providing enough correction, put in a thicker ring. If it is effecting too much correction, put in a thinner ring.

Since U.S. Food and Drug Administration (FDA) approval, I have performed about 100 procedures on patients and I also have removed Intacs rings. My enhancement rate, since approval, has been 2/100 or 2%. Other surgeons can expect similar results.

I cannot underscore enough the point that if you do the procedure correctly and select the correct patients, the amount who either need an exchange or removal should be extremely low.

During the learning curve, though, there will be patients who get astigmatism just because of wound manipulation. This is a new surgical skill for many surgeons and one must learn to do it properly. The nice thing about the learning curve with this procedure is if you really create a lot of astigmatism, or if you really miss the power, you can just take the implants out and start over with LASIK or PRK.

This is a valuable option, compared with the choices left after an unsuccessful LASIK. If you have performed a LASIK procedure that is decentered, a patient is unhappy with glare, or if a patient is unhappy with the correction, you do not have that option to just go back to ground zero again.

Explantation of Intacs, followed by LASIK and PRK or any other corneal procedure, would only be used in the event that the patient was unhappy with the Intacs and they still wanted a permanent, refractive, corrective procedure performed.

During the clinical trials, we explanted several Intacs and performed PRK or LASIK. These patients did extremely well.

Intacs after LASIK

Intacs can be used following a corneal refractive procedure, providing a patient retains good pachymetry. If patients have had a maximum of LASIK, either because their cornea is as thin as the surgeon wants to make it or if they feel that they are still undercorrected or have halos, the Intacs can be implanted to treat low, residual myopia.

The procedure to treat residual myopia after LASIK is identical to a standard Intacs procedure. If you have a patient with residual myopia of between 1 D and 1.5 D, obviously it is very easy to lift the flap and just do a few extra pulses and avoid the expense of the Intacs.

But if the surgeon feels more laser pulses could be dangerous because the cornea is as thin as he or she is comfortable with, the Intacs provides another option. I prefer to have 250 µm residual tissue below the LASIK flap, or 410 µm total. I would prefer to do an enhancement with an Intacs even though there is additional expense, because it is safer for the patient.

Patient selection

Patient selection for Intacs correction of residual myopia following LASIK or PRK is the same as for initial Intacs implantation. Patient selection for Intacs segments is fairly well defined by the 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. Generally, we are looking for low post-correction myopia, astigmatism less than 1 D, so the same inclusion criteria that I would use for a standard Intacs procedure applies.

New rings coming

Currently, Intacs are available in three thicknesses: the 0.25 mm corrects from –1 D to –1.75 D, the 0.3 mm corrects from 1.75 D to 2.25 D and the 0.35 mm corrects from 2.25 D to 3.25 D. KeraVision currently is working on three new rings that expand the possible range of correction. Two thicker rings of 0.4 mm and 0.45 mm and one thinner ring of 0.21 mm will expand the range of correction from –0.75 D to –5 D.

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 is an employee of KeraVision Inc.

Reference:

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