contact lens business
Update: Corneal Reshaping Therapy
An evolutionary leap from orthokeratology, this method of vision correction is coming into its own.
By Bruce Koffler, M.D.

Like continuous wear 30-day contact lenses, corneal reshaping therapy is still shaking off the doubts and concerns raised by its previous incarnation -- orthokeratology. But today, using specially designed contact lenses to reshape the cornea and correct refractive error is far more effective than early techniques. As a result, interest in corneal reshaping therapy is spreading rapidly, and more research is being devoted to it. This, in turn, is leading to new techniques and technologies.

Here's a quick update.

Today vs. Yesterday

Today's corneal reshaping lenses are different from the old ortho-K lenses in several significant ways:

Material and design. The old lenses were hard and fit flat, which could cause corneal distortion, abrasion and warpage; this sometimes left the patient with poor image quality. In contrast, today's new reverse geometry designs are computer-generated, often with the help of sophisticated topographic software, using high-DK materials. Problems with corneal warpage have largely been eliminated.

Precision fit. Some new lenses, such as the Paragon Corneal Refractive Therapy (CRT) lens, let you make specific adjustments to different sections of the lens. Paragon's CRT lens has three concentric zones -- a central Optical Zone, a Return Zone in the mid-periphery, and the Landing Zone in the periphery -- that can be modified to better fit your patient. (The lenses are created using "optoform 50" lathes; Paragon uses interferometers to check the surfaces and the edges.)

Amount of refractive error that can be corrected. The old ortho-K lenses could only improve vision by 1 to 1.5D. Today's corneal reshaping lenses can correct as much as 4 to 5D of refractive error, and in some cases can also control astigmatism.

	When fitting a lens to achieve corneal reshaping, the ideal lens will have a "doughnut" fluorescein pattern like the one on the left. The lens on the right is too steep and needs to be flattened.

Time required for successful treatment. Ortho-K techniques took as long as a year to be successful. Today, corneal reshaping can be safely accomplished within weeks, days or even hours.

How Does the Process Work?

Research conducted by Helen A. Swarbrick, O.D., Ph.D., FAAO, suggests that reverse geometry corneal reshaping lenses produce their refractive effect by remodeling the anterior corneal layers, rather than by bending the overall cornea. Thinning in the central corneal region appears to be primarily epithelial in origin; thickening in the midperipheral area includes a stromal component.

Who is a Good Candidate?

John Mountford, M.D., has shown that because the corneal contour that results from corneal reshaping is oblate, the greatest myopic reduction occurs when an eye has three characteristics:

• positive corneal eccentricity
• steep corneal curvatures
• large horizontal iris diameters.

A positive e-value (corneal eccentricity) indicates a normal corneal shape -- i.e., the cornea is steep centrally and flattens gently in the periphery. This eye is a good candidate for corneal reshaping. A zero e-value indicates a perfectly spherical cornea -- a poor candidate. A cornea with a negative e-value is already oblate, which is the contour produced by corneal reshaping, so corneal reshaping would have little or no effect.

Many of today's topography systems can provide a precise measure of e-value.

New Horizons

Corneal reshaping offers low myopes refractive correction that doesn't involve surgery, is reversible, and doesn't require wearing a contact lens every day. But new possible uses for corneal reshaping are also beginning to appear. Two noteworthy developments:

Post-refractive surgery adjustment. As you know, post-op corneas seem to be more elastic and are more prone to change than virgin corneas. Radial keratotomy (RK), for example, is often followed by problems of diurnal variation and progressive hyperopia 3 to 4 years after surgery. Now researchers are finding that corneal reshaping conducted post-surgery may be especially effective, and may produce permanent correction, especially if performed within a few months of the surgery.

In a study involving 21 eyes of 12 patients that I co-authored in 1999 ("Achieving Additional Myopic Correction In Under-corrected Radial Keratotomy Eyes Using The Lexington RK Splint Design," CLAO Journal, Jan. 1999, Vol. 25, No.1), uncorrected visual acuity improved by an average of 3.4 lines, and among patients who were treated within 7 months of their last RK procedure, 60% remain glasses and contact lens free months to years after contact lens wear was discontinued. (Note that this study was conducted before the introduction of reverse geometry design lenses using plateau-shaped RGP lenses.)

Pharmacologically assisted correction of hyperopia. J. E. McDonald, M.D., and Allyson Mertins, O.D., are using NSAID drops such as Acular to soften the cornea before using corneal reshaping to correct residual hyperopia following LASIK, PRK or RK. (Of course, using meds to soften the cornea might work for myopia, too.)

Reshaping the Future of Eye Care?

Corneal reshaping therapy is an exciting modality, and offering it has definitely enhanced my practice. Our low myope patients appreciate having a non-surgical option that doesn't involve daily contact lens wear. And with technology making the lenses more precise and new possibilities for treatment appearing every year, the future for corneal reshaping looks bright indeed.

I'd encourage all ophthalmologists to keep an eye on this field, and consider adding this modality to their own practices.

Dr. Koffler is director of the Kentucky Center for Vision in Lexington, Ky., and associate clinical professor of ophthalmology at the University of Kentucky Medical Center. He is past president of the Kentucky Academy of Eye Physicians and Surgeons, and current president of the Contact Lens Association of Ophthalmologists.