Ten Common Questions About Today's Ortho-k

While you consider incorporating orthokeratology into your practice, you'll likely develop a few questions. This article may help you find the answers.

BY RODGER T. KAME, OD
OCTOBER 1998

Orthokeratology has experienced a revival with the development of reverse geometry lenses and their use in accelerated orthokeratology. The recent approval by the U.S. Food and Drug Administration (FDA) of contact lenses for use in daily wear ortho-k has further enhanced the legitimacy of the procedure.

The following are questions you may have as you consider ortho-k for your own practice.

1. DOES THE RECENT APPROVAL OF A CONTACT LENS FOR ORTHO-K BY THE FDA INCLUDE BOTH DAILY AND OVERNIGHT WEAR?
   No. The approved application by the FDA is for daily wear only. Specifically, the Contex OK reverse geometry RGP lens is indicated for daily wear orthokeratology for the temporary reduction of myopia up to -3.00D. The clinical data submitted by Contex, Inc. demonstrates that the average reduction in myopia is 1.69D with a range of 0.25D to 4.25D.
2. CAN I ORDER REVERSE GEOMETRY RGPs FOR ORTHO-K FROM MY LABORATORY OF CHOICE?
   A qualified yes. As an off-label prescription, you may instruct your preferred laboratory to fabricate a reverse geometry lens for daily wear ortho-k, according to Dr. James Saviola, chief of the FDA Vitreo-retinal and Extraocular Devices Branch. Without FDA approval, however, laboratories may not legally design and market their own orthokeratology contact lens design, as Contex Inc. can now do.
3. CAN I OFFER ORTHO-K AS AN OPTION TO ALL OF MY REFRACTIVE SURGERY CANDIDATES?
   Yes. However, the change in corneal contour that provides the reduction in myopia and astigmatism is largely determined by corneal eccentricity, so the greatest reduction you can expect is about 2.50D to 3.00D. The average cornea has an eccentricity of approximately 0.5 and each 0.1 reduction in eccentricity value accounts for a myopic decrease of about 0.50D. Thus, ortho-k may benefit your lower myopes who are considering refractive surgery.
4. HOW IS TODAY'S ORTHO-K DIFFERENT FROM THAT OF THE 1960s, 70s, AND 80s?
   Today's ortho-k is largely different. What was once a one- or two-year procedure is now about a three-month procedure due to the new contact lens designs that I call reverse geometry lenses. This configuration incorporates steeper peripheral curves which permit good lens centration, as well as distribution of positive pressure on the corneal apex and negative pressure in the midperiphery.
   Traditional ortho-k utilized rigid lenses that were modified as the cornea sphericized (the process by which the corneal eccentricity reduces or by which the corneal prolate ellipse changes to a spherical shape). The lens-to-cornea relationship was decreased by reordering lenses with flatter base curves or by reducing the primary optical zone diameter. A major limitation was that lens centration was difficult to achieve, often resulting in asymmetric with-the-rule (WTR) corneal astigmatism.
5. DO I NEED A COMPUTERIZED CORNEAL TOPOGRAPHER TO DETERMINE WHETHER OR NOT MY PATIENT IS A CANDIDATE FOR ORTHO-K?
   Mapping is useful to accurately determine whether or not your patient has a corneal contour that's conducive to change. A corneal mapping device is not necessary for a clinician to begin implementing the concepts of accelerated ortho-k. For designing lenses and for monitoring corneal changes, mapping devices are most effective. A computerized program by John Mountford of Brisbane, Australia, requires the input of the average central corneal radius and the average corneal eccentricity determined by computerized mapping. This program will generate a lens design that provides the appropriate tear reservoir to result in predictable corneal flattening over a large 4.0mm to 6.0mm corneal chord. The Contex B Series, developed by Tom Rheim, Jim Day and Nick Stoyan also utilizes tear lens profiles based on sagittal or elevation maps. This data is best derived by corneal mapping and thus helps reduce the number of lenses required to complete the corneal changes.
   Corneal mapping is essential in determining whether or not an ortho-k procedure will reduce astigmatism. According to Mountford, limbus-to-limbus corneal astigmatism has a poor outcome, whereas WTR corneal toricity that's primarily located in the central cornea has a good chance of being reduced up to 2.00D.
6. WHAT IS AN IDEAL CORNEAL CONTOUR?
   The most ideal corneal contour is a steep, large cornea which would have the highest eccentricity. Keep in mind, though, that steeper corneas tend to have smaller horizontal visible iris diameters (HVID) and lower eccentricities. Larger corneas have flatter Ks and thus, may also have lower eccentricities. However, 90 percent of normal corneas are prolate ellipses having average eccentricities between -0.45 and -0.55. With successful reverse geometry lens application and the central cornea reaching a spherical (e = 0) or an oblate ellipse, you can expect maximum myopia reduction of about 2.50D.
7. DOES THE VOLUME OF THE TEAR RESERVOIR INFLUENCE ORTHO-K EFFECT?
   Tear reservoir volume is very important. In fact, the profile and volume of tears is more important for determining the amount of corneal change than the flatness of the base curve.
   There are two ways to maximize the amount of ortho-k effect. Ensuring a deep tear layer thickness of 70 to 90 microns results in larger myopia reduction but has a smaller zone of flattening and may result in night vision flare. Another way to maximize effect is by increasing the width of the tear reservoir by using larger diameter lenses having fixed peripheral widths. These lenses allow a wider area of pooling before the reverse curve bearing begins and on average, maximize a 2.50D myopia reduction with a desirably larger area of central flattening.
8. CAN I PERFORM IN-OFFICE MODIFICATIONS ON REVERSE GEOMETRY LENSES AS I DO ON CONVENTIONAL RIGID LENSES?
   Lens binding, or sticking, appears to be the most common problem for which in-office modification may help. Simple in-office polishing may remobilize a lens when a light film develops on its surfaces.
   This is also an important step in reducing central stipple stains that result from the traumatizing effect of light surface deposits. You must address all marginal dry eye cases to minimize factors that reduce corneal and lens wetting. Lens edge profiles may require modification for comfort, but the blending of secondary curves common in conventional RGPs is not possible with reverse geometry lenses.
9. THE TIME REQUIRED TO FIT AND MANAGE ORTHO-K PATIENTS SEEMS CONSIDERABLE. HOW CAN I OFFER A REASONABLE FEE FOR MY PROFESSIONAL SERVICES?
   Those who are inexperienced but wish to develop a comfort level might consider staged fitting fees, whereby you fit the patient in stages and charge by your regular fitting fee first for the basic spherical lens fit. Once you successfully complete the basic spherical fit, the second stage initiates the fitting of reverse geometry lenses to reduce generally around 2.50D to 3.00D of myopia in an accelerated manner. The first stage fees minus the initial comprehensive exam fee is a suggested level of compensation for the second stage. You may add a third stage for difficult cases or for overnight wear (when it is FDA approved), or as a yearly fee for the following year, which may include lens fit updating and management. The global fee option has been the mainstay of orthokeratology over the years. The global fee for accelerated orthokeratology, for example, may be a flat fee ranging from $1,200 to $2,000 for one to two years of professional services, including materials and office visits.
10. WHAT UNIQUE PHYSIOLOGICAL CONCERNS SHOULD I LOOK OUT FOR WHEN MANAGING ORTHO-K PATIENTS?
    Fortunately, the availability of high Dk RGP materials for reverse geometry lenses has made corneal edema an uncommon problem. Lens binding and transitory superficial epitheliopathies, however, are common. In patient selection, watch for patients with against-the-rule (ATR) corneal toricity or those with ATR refractive astigmatism combined with WTR corneal toricity. As the cornea sphericizes, internal astigmatism manifests, and although myopia reduces, ATR refractive astigmatism increases and likely hampers vision.

Final Advice

Does incorporating orthokeratolgy into your practice require special skills and management? Ortho-k requires fitting diligence -- as expected with keratoconus patients. Good clinical expertise in rigid lens fitting is a must. Skills such as fluorescein pattern and corneal map interpretation are fundamental to safe, successful accelerated orthokeratology. Acumen in rigid lens optics and design and good slit lamp techniques are also essential. The Orthokeratology Society of Australia requires that computerized corneal topography be utilized in managing ortho-k patients.

Orthokeratology must be performed responsibly, or poorly managed ortho-k cases may lead to bad press and may set back acceptance of the procedure by both consumer and profession. For the innovative, specialty-oriented contact lens practice, accelerated orthokeratology is an opportunity waiting. For the mainstream practice, the opportunity of diversifying your options for patients may be a matter of survival in today's refractive surgery and managed care environment.

Dr. Kame is in practice in Los Angeles, Calif., and is a diplomate in the Cornea and Contact Lens Section of the American Academy of Optometry. He is a past chairman of the Contact Lens Sections of the AAO and the AOA. He is a trustee on the College Board at the Southern California College of Optometry, where he is also an adjunct associate professor.