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A Different Approach to Ortho-K

Three steps to facilitate the fitting process and, thus, grow your practice

BEN LARSON, O.D., SANFORD, FLA.

Remember how you were taught to fit an RGP lens in optometry school? It was simple: You had base curves, in millimeter radius or diopters (most prefer the latter), an overall diameter, and if you wanted a little more customization, you added some peripheral curves. Further, if you wanted to customize the design, you added an optic zone diameter.

Guess what? Fitting for orthokeratology — a lucrative niche — can be just as easy if you follow these steps.

1 Translate proprietary fitting language

Many O.D.s don’t offer orthokeratology because each lens design has its own proprietary fitting language. To get past this roadblock, grab a Tyler’s Quarterly, and call RGP lab consultants and ask them for help in translating this proprietary language into the design parameters taught in optometry school. Doing so enables you to become an expert in the fitting process. By becoming an expert, you can become your own orthokeratology consultant, create your own fitting set, reduce chair time and lab costs, improve patient retention and increase your volume of patients.

In following this step, I found that many lab consultants could communicate in common terms the designs they fabricated.

2 Network and obtain certification

Join The Orthokeratology Academy of America (www.orthokacademy.com), and attend its annual symposium. Also, obtain certification to fit the several designs. (See “Orthokeratology Companies,” below.)

In addition, reach out to colleagues about their fitting methods. During my journey to accomplish this, I learned that some colleagues performed their own in-office lens modifications, and I was able to actually meet with an inventor of a commercial design and pick his brain.

3 “Reverse-engineer” proprietary designs

Use the NAFL patterns of the proprietary designs to approximate their curve widths and depths, so you can “reverse engineer” them and create a custom trial lens set.

My set is comprised of 114 lenses, which consist of three sets of 38 lenses in a steep, median and flat peripheral curve arrangement. I standardized the curves based on an average corneal curvature of around 43.00D with an average of -3.00D of myopia. Each lens is a six-curve design with a “double reverse curve.” Essentially, the reverse curve is 6mm in width consisting of 2mm and 3mm curves. The first reverse curve is 2.00D steeper than the second reverse curve peripheral to it. Each trial lens is also 10.4mm in diameter, has a 6.0 S posterior optic zone and a .20 S center thickness.

I wrote every curve on the flat pack for each trial. Also, I incorporated an over-correction and power modification of +0.75 into each trial. This made the fitting process easy to understand and modify. Once the closest trial was fit and over-refracted, an exact order was given to the lab with minor adjustments, if any. My learning curve shot straight up, making tweaking every aspect of the design a breeze.

Finally, I created my own custom design and later named it the Advanced Ortho-K (AOK) lens after our practice name Advanced EyeCare. (See “Case Report,” below.)

Case Report

C.D., a 33 year-old female with no remarkable ocular health issues, presented for orthokeratology. Her manifest refraction was -4.25-0.75x068 OD and -5.25-0.50x117 OS. C.D.’s keratometry readings were 4425@122/44.50@032 OD, 44.00@070/44/50@160 OS. Her topography showed typical aspheric curvatures and mild oblique astigmatism, which correlated with her keratometry findings. Her eccentricity values were .38 OD, .44 OS.

The best trial lens parameters below show the curves and corresponding widths written from the center (optic zone) of the lens, to the periphery. Reading from left to right, the first curve is the central base curve, or optic zone. The second and third curves are the reverse curves, and the fourth, fifth and sixth curves are the alignment, or peripheral curves. Also written at the end is the center thickness and overall lens power for best vision while the lens is worn.

Best Trials: OD: 39.75,4900/3,4700/3,4325/6,4225/6,2725/4,20ct,+0.75 lens power,10.4 diam,6.0 OZ OS: same

Initial Order: OD: 3775,5000/4,4800/4,4325/6,4225/6,2725/4,20ct,+1.25 lens power,10.6 diam,5.8OZ OS: 3750, 5000/4,4800/4,4325/6,4225/6,2725/4,20ct,+1.25 lens power,10.6 diam,5.8OZ

The same trial lens above fit perfectly in both eyes. The over-refraction was -1.50 OD, -1.75 OS. Due to C.D.’s high myopia, I needed to be slightly more aggressive with the initial order to get the full correction.

This case demonstrates the advantage to knowing every nuance of a design to intelligently make subtle tweaks. To get the desired outcome, I noted a flatter central base curve in the optic zone than required for a plano over-refraction with my standard +0.75 lens.

For example, a 38.25 central base curve OD would have netted a plano over-refraction, but I ordered a 37.75 central base curve for a little extra flattening of 0.50. Also, I decreased the overall optic zone diameter from a 6.0 to a 5.8 while increasing the reverse curve diameters from .3s to .4s. The slightly smaller optic zone (OZ) and wider reverse curves (RC) allow for a more pronounced orthokeratology effect at the slight expense of a smaller OZ and possibly more glare and flare at night if the patient has small pupils (under 4mm in light and less than 6mm in dark) Fortunately, this patient has pupillary diameters in light/dark of 3.5mm/5.5mm. I also steepened the RCs for a better “push-pull” effect between the central base curve and RCs.

I fit this patient a little more than a month ago. She was seeing 20/20 uncorrected OU at 1.4 weeks.

C.D.’s topography showed typical aspheric curvatures and mild oblique astigmatism, which correlated to her keratometry findings.

Ahead of the curve

Follow the three steps outlined above, and you too can seamlessly incorporate orthokeratology into your practice, slowing myopia progression in children and young patients, enabling spectacle-free vision, creating patient loyalty and increasing practice revenue. OM

Dr. Larson practices at Advanced EyeCare (www.advancedeyecareflorida.com) with his wife, Christy. They opened a paperless practice in 1998. E-mail him at drbenlarson@gmail.com, or send comments to optometricmanagement@gmail.com.