Shelving the Microkeratome in
Favor of the Laser

BY JAMES V. AQUAVELLA, M.D.
JAN. 1996

Now that we've seen the initial round of FDA approvals for excimer laser PRK, we can consider what the future of refractive surgery will be -- including some new developments in one of the oldest refractive surgical techniques.

KERATOMILEUSIS

In 1969, Jose Barraquer introduced keratomileusis at the First World Corneal Congress in Washington, D.C. With this technique, which involves a long, steep learning curve, the surgeon uses a microkeratome to remove a slice of lamellar corneal tissue. The microkeratome is fitted to the eye with a suction ring, upon which is mounted a glide and a guillotine blade.

Despite incremental improvements in microkeratome design and technique, this instrument is still the single greatest drawback to successful keratomileusis refractive surgery. It's cumbersome and difficult to handle, and it must be maintained in pristine condition to avoid mechanical failure.

LASIK

Laser in-situ keratomileusis (LASIK) is a recent modification of Barraquer's procedure. With this method, termed "flap and zap," the surgeon uses the microkeratome to create a lamellar corneal flap, and then ablates a specific amount of intrastromal tissue with an excimer laser. The surgeon then replaces the corneal flap in its original position on the eye.

While this technique is an improvement over the original keratomileusis procedure because it requires only one pass of the microkeratome, the fact that the instrument is still an integral part of the procedure continues to be a drawback.

One important benefit of LASIK is that the central epithelium is not disturbed, thus promoting rapid rehabilitation of the eye.

PICOSECOND LASER

Over the past few years, we have used the Nd:YLF picosecond laser for intrastromal ablations in the laboratory. A very recent innovation enables us to use the picosecond laser instead of the microkeratome to cut the keratomileusis flap. We can then use the excimer laser for subsequent myopic and hyperopic corrections, just as we do in LASIK.

This modification of the original Barraquer keratomileusis procedure is a major development. It simplifies the surgery and eliminates the need for the cumbersome microkeratome. However, it does incur the additional expense to the surgeon of a second major ophthalmic laser.

THE NEW VS. THE FAMILIAR

These new laser-assisted keratomileusis techniques will invariably be compared to radial keratotomy and photorefractive keratectomy. Although still in its infancy, PRK has become the standard refractive surgical procedure worldwide. Any comparison is difficult because true prospective studies have not been concluded. Considering the rapid advances that occur in technology, any five-year prospective comparative study will be obsolete before it's completed.

With standard keratomileusis surgery, the potential for a disaster -- a perforation, lost corneal button, or interface scarring -- is clearly greater. But in the hands of an experienced keratorefractive team, the incidence of such problems is probably low.

THE NEXT GENERATION

Incisional techniques will still have a place in refractive surgery, but clearly lasers represent the wave of the future. Computer-driven stereotactic laser surgery, where the computer's sensors direct the procedure, will undoubtedly lead to more predictable and dependable results, and enable the high volume of procedures needed to be cost-effective.

The primary consideration for refractive surgery in the United States will probably be: Can this procedure be performed in high volume with reproducible results in order to be compatible with current cost expectations? Clearly PRK has a strong lead and it will be difficult for other types of procedures to meet this standard. CLS

Dr. Aquavella is chairman of the Genessee Valley Eye Institute and director of the corneal research lab at the University of Rochester.