Article Date: 5/1/2001

Orthokeratology
Getting Started with Accelerated Ortho-K
In Part 2 of this two-part series, you'll learn how to equip yourself with the right tools, select the best candidates and manage the process in your patients.
BY ROBERT C. BAUMAN, O.D., Woodbury, Conn.

Over the past 5 years, we've had major advances that have made accelerated orthokeratology a reality. These advances include improvements in computer controlled lathing technologies, which have enabled the creation of reverse geometry lenses, ultra-high Dk gas permeable rigid lens materials and corneal videokeratoscopy.

I've had a lot of success with this procedure. Patients can experience dramatic results, and it's a real practice-builder.

PHOTO BY PAT SIMIONE

You may already know about this modality, but if not, accelerated orthokeratology refers to the process of using reverse geometry ultra-permeable rigid contact lenses to reduce low to moderate amounts of myopia, as well as small degrees of with-the-rule astigmatism. Unlike traditional ortho-K, which often took several years to produce clinically significant refractive changes, accelerated ortho-K can produce twice as much corneal flattening as traditional ortho-K techniques.

Recently, there have been several four-zone lenses that are being investigated that have the benefits of accelerating the process even further. Using these four-zone lenses may only require one pair of lenses to produce the desired effect, as opposed to several pairs of lenses.

Last month, in part one of this series, I discussed how I set my practice apart from the competition by offering this service. I also mentioned methods for marketing this modality to your patients.

This month, I'd like to talk more about the essentials for getting started with accelerated ortho-K, plus I'll discuss how to select the best patients and give you a rundown of lenses available for accelerated ortho-K.

The essentials

Three elements -- namely advances in corneal videokeratoscopy, reverse geometry lenses and hyperpermeable RGP lenses -- are the technologies responsible for making accelerated ortho-K possible. Here's a closer look at the importance of each technology's role in this procedure.

  1. Corneal topographer. You must have an accurate corneal topographic map of the potential candidate to begin the fitting process. Without one, it would be like trying to navigate in a foreign country without the benefit of a comprehensive map.
  2. Reverse geometry rigid gas permeable (RGP) contact lenses. These lenses enable dramatic, rapid myopia reductions.
    Reverse geometry lenses have a secondary curve that's steeper than the base curve radius (BCR). This curve has two functions. It improves lens centration and contains a tear reservoir, which increases the procedure's speed and efficacy.
    Many practitioners unfamiliar with ortho-K think that a reverse geometry lens simply presses on the central cornea and flattens the eye. This is incorrect. Rather, a reverse geometry lens is fitted to give an apical tear layer thickness of about 10 microns. The steeper secondary curve forms a ring-shaped tear reservoir around the cornea's central portion. This causes positive pressure on the central cornea and negative pressure in the tear reservoir area. A properly fit lens has little or no central touch.
  3. Hyperpermeable RGP lens materials. Hyperpermeable RGP lens materials for extended wear are the greatest advancement for this procedure. RGPs have many advantages over soft lenses for extended wear. They can produce less corneal hypoxia, and they're associated with a lower incidence of microbial keratitis.
    For accelerated ortho-K, lens materials with a Dk of 50 or more are best for overnight wear.

Selecting the best patients

Two groups I've found to be particularly interested in ortho-K are the following:

Fitting considerations

Suitable candidates will likely achieve 20/20 vision or better vision OU after several days or weeks of wearing the lenses at night for 8 to 10 hours. After several months of night wear, patients may only need retainer lenses 3 to 4 nights per week to retain the alterations.

Generally 1.00D to 2.00D myopes with corneal eccentricity values in the range of .5 to .8 make ideal candidates. A small amount of with-the-rule (WTR) astigmatism <1.00D is usually easy to correct as well.

Also, much evidence in the literature and in my personal experience have shown that patients who've previously worn RGPs are less successful candidates because RGPs mold the cornea spherically. If a patient stops wearing his RGPs for several months, you can then accurately evaluate whether he's a candidate for the procedure. After discontinuing RGP wear, these patients are really as good a candidate as any non-RGP wearer.

It's critical to educate potential candidates about the benefits and limitations of accelerated ortho-K. They must understand that in all cases, night time lens wear is required for as long as they wish to maintain the gains derived from the procedure.

Gauging E values

Before determining whether a patient will be a good candidate for accelerated ortho-K, you must calculate the patient's corneal eccentricity, otherwise known as the E value.

The corneal shape is commonly described as a prolate ellipse because the radius of curvature flattens gradually from the apex of the cornea to the periphery. The amount of flattening is the E value. The higher the eccentricity, the faster the rate of flattening and the greater the difference in curvature between the apex and the periphery.

Corneal eccentricity values range from zero (spherical shape) to 1.00 (parabolic), with the average E value being .50. Generally, practitioners agree that a change of 1.00D in refraction is accompanied by a .20 reduction in corneal eccentricity.

You can usually achieve myopia corrections ranging from plano to 4.00D and up to 1.50D of WTR astigmatism.

A look at the available lenses

In May 1998, the FDA approved the first lens specifically indicated for ortho-K, the Contex OK lens. This three-zone lens is approved for daytime wear.

Other lens designs for this procedure include Paragon's Corneal Refractive Technology (CRT), a lens design by Euclid and one by Correctech. All three of these lens designs are currently undergoing clinical trials for FDA approval of overnight ortho-K use.

Edward S. Bennett, O.D., M.S., F.A.A.O., associate professor at the University of Missouri-St. Louis School of Optometry, is working with Paragon on their lens. According to him, the CRT lens design isn't expected to gain approval from the FDA until sometime next year.

Lens manufacturers will have trial lens fitting sets which, when combined with clinically validated nomograms, help you select initial base curves and diameters. I recommend that you have several fitting sets of reverse geometry lenses.

After fitting a patient with these lenses, check the fit with fluorescein angiography. The fit is good when the fluorescein patterns show a small amount of central touch, good lens centration and a little lens movement after blinking.

Generally, I expect that each patient will require two pairs of lenses. Most patients need their second (final) pair of lenses (retainer lenses) about 6 to 8 weeks after beginning the process.

Effectively managing patients

In my practice we see all patients the day after their first night of wear. They arrive wearing their lenses, and we remove the lenses only after evaluating the fit. It's not uncommon to have a 2.00D myope seeing 20/20 uncorrected on his first follow-up visit.

If it's going well, we see patients next at 1 week, 2 weeks and each month for the first 6 months. After patients have retainer lenses and vision stabilizes, we see them every 3 to 6 months.

Most doctors find that gearing up for this procedure requires a significant investment of time and money to educate and equip themselves. But once mastered, this service can improve your bottom line, your professional image and most important, it will enable you to offer your patients the latest technology to safely improve their vision.

Dr. Bennett leaves us with his thoughts: "I really think that there's tremendous potential, and the newer designs appear to be very successful in terms of reducing myopia quickly and patient satisfaction," he says. "There's also tremendous consumer interest in myopia reduction." 

Dr. Bauman is a research and development consultant for Vistakon. E-mail him at bauman@pcnet.com.


Optometric Management, Issue: May 2001