REFRACTIVE SURGERY:

Where Do We Go From Here?

Here's a look at the vision correction options that might be available to your patients in the not-so-distant future.

By James V. Aquavella, M.D.
FEBRUARY 1999

There has been a very significant increase in the number of refractive surgery procedures performed -- an almost tenfold increase from the first quarter of 1996 to the last quarter of 1998. Many eyecare professionals envision continued increases of the same magnitude. The potential for growth in refractive surgery is enormous, considering that 50 percent of the world's population requires some form of vision correction. In the United States alone, 140 million individuals use eyeglasses or contact lenses. It's estimated that excimer laser procedures alone (PRK and LASIK) will increase by almost 50 percent in 1999.

While laser vision correction constitutes the largest segment of the refractive surgery market, the introduction of new technologies, such as laser thermal keratoplasty, phakic intraocular lenses, and intrastromal corneal rings will become important additions to the refractive surgery armamentarium. Interest in refractive surgery procedures among both patients and practitioners is escalating.

Orthokeratology

There has been some renewed interest in orthokeratology as a refractive procedure, but its potential use is limited. Some of the drawbacks include expense, a time-intensive fitting process and an end result that needs to be maintained through contact lens wear. Therefore, I don't believe orthokeratology will play an important role in the correction of refractive errors in the future.

Microkeratomes and Lasers

Radial keratotomy is still useful in special situations, but will continue to decline in popularity. It isn't state-of-the-art or as reliable as PRK or LASIK, and the long-term stability isn't as good, but good refractive surgeons continue to keep it in their bag of tricks. It still has a place for cases of undercorrected PRK, for patients with only one or two diopters of myopia who can't afford PRK, for postoperative grafts and in third-world countries where other technologies are currently unavailable.

Automated lamellar keratoplasty (ALK) has largely been replaced by LASIK. Although PRK continues to lose market share to LASIK, it has been utilized for more than a decade and is clearly the standard by which other refractive surgical procedures must be compared. Recent studies indicate that 90 percent to 98 percent of patients achieve 20/40 or better uncorrected acuity, with 75 percent to 80 percent in the 20/20 range. Innovations in PRK technology include scanning technology and the FDA approval for moderate myopia, astigmatism and hyperopia.

Excimer laser manufacturers that offer an FDA-approved device include VISX, Summit, Autonomous Technologies and recently, Nidek Co., Ltd. The FDA has expressed concern in the recent past about the use of unapproved, black box lasers for refractive procedures. However, there have been so many FDA approvals and there are many more in the pipeline, so the incentive to use a black box laser is decreasing. To go the black box route, you have no company behind you and you don't have access to benefits like free upgrades. A black box laser has to be a quantum ahead of anything else before I will even consider it.

At the core of LASIK procedures is microkeratome technology. Bausch & Lomb's Chiron microkeratome systems are utilized in over 80 percent of LASIK cases. There has been a resurgence of interest in disposable keratomes and in the new water jet technology, but surgeons will be reluctant to switch to other keratomes unless there is a very significant potential for improvement due to the fear of potential flap complications associated with relatively untested technology.

Ring Around the Cornea

The KeraVision intrastromal corneal ring, a fine ring of PMMA inserted into the periphery of the corneal stroma, may gain FDA approval in 1999. Depending upon the thickness and width of the ring, it creates varying degrees of corneal flattening and subsequent reduction in myopia. The results of the six-month clinical studies have been promising and are roughly equivalent to those of PRK. The cost of the technology to the physician and perhaps the patient will be significantly lower than PRK or LASIK.

The procedure is reversible, but the learning curve is significantly steeper than for PRK. Surgeons must learn how to insert the ring, where to place it and how deep to place it. It may take 10 to 20 procedures for the surgeon to become comfortable implanting the intracorneal ring, while a practitioner performing PRK can become comfortable after only one or two procedures.

Laser Thermal Keratoplasty

Laser thermal keratoplasty (LTK) involves application of a holmium laser to heat and shrink paracentral corneal collagen, reducing hyperopia. Phase II clinical trial outcomes in the low hyperopic patient group have yielded acuities of 20/25 or better in 60 percent of patients, and 20/40 in 88 percent of patients. FDA approval for the procedure is also anticipated later this year, although there continues to be some skepticism regarding the potential for long-term regression.

Intraocular Procedures

The intraocular procedures for refractive surgery include implantable contact lenses or phakic intraocular lenses. Targeted for high myopia and hyperopia, these procedures will probably not gain FDA approval until after the year 2000. The fear of long-term complications may affect FDA approval as well as surgeon acceptance. Nevertheless, the risk-benefit ratio may prove favorable for correcting higher degrees of ametropia.

Impact on the Contact Lens Market

Despite the anticipated growth of refractive surgery, it is not expected to decimate the vision care (contact lenses and spectacles) market in the near future. It seems that even though refractive surgery is increasing by leaps and bounds, there has recently been an unexpected expansion in the contact lens market after being relatively stable for many years. There's also clearly a reluctance of the population to consider refractive surgery, as we're still dealing with a refractive surgery adoption rate for the target population of less than 1 percent. Another obstacle is the cosmetic spectacles market. Some people would choose to wear their designer spectacles even if their myopia were eradicated.

On the other hand, refractive surgery is especially appealing to contact lens wearers because contact lenses still constitute a hassle. They're better today than ever because patients no longer have to carry a backpack with 17 different containers to take care of them, but they still have to put them in and take them out. Frequent replacement and disposability make it even easier, but they also increase the cost to the patient, especially in toric lenses. Presbyopic correction remains the biggest untapped market for both contact lenses and refractive surgery. We don't know what breakthroughs in bifocal correction lie ahead, but we do know that we can now change the optics in the cornea the same way that we change the optics in a contact lens design. Thus, most changes achieved in a contact lens can also be achieved through refractive surgery. In all facets of future vision care, the possibilities are tremendous. CLS