When driving to a new destination, how do you decide which way to go? Navigation apps give various options—shortest distance, quickest time, and/or avoiding construction or traffic. Orthokeratology (ortho-k) is similar—you know where you want to go, but you can take different routes to get there.

Methods of Fitting Ortho-k

Various methods to fit ortho-k patients include empirical, diagnostic evaluation, fitting nomogram, topography-based software, and diagnostic evaluation after one night of wear.

Empirical Employing this method, lenses are ordered from exam findings—refraction, keratometry, eccentricity, and horizontal visible iris diameter (HVID); diagnostic evaluation of a lens on the eye is not necessary. Findings are sent to the manufacturer, and lenses are then designed and manufactured using the company’s proprietary formula/design. If initial designs do not provide optimal results, subsequent lens changes are made based on refractive and topographic results reported to the manufacturer.

Diagnostic Evaluation This technique uses lenses with known specifications of sagittal depth, base curve, reverse curve, alignment curve, and overall diameter that are evaluated with sodium fluorescein (NaFl) at the slit lamp. Initial lens selection is based on exam findings (keratometry, topography, manifest refraction, HVID, and eccentricity). Then, on-eye evaluation relies on the practitioner’s judgment of centration and the NaFl thickness under the lens in the treatment zone, reverse curve, alignment zone, and at the edge. If necessary, adjustments of specifications are made by the practitioner to create the ideal fitting relationship (Figure 1).

Fitting Nomogram This method uses two parameters (spherical component of manifest refraction and flat K reading) with a template to select an initial trial lens, which is evaluated at the slit lamp with NaFl. This determines whether that lens is dispensable or whether modifications are necessary. One manufacturer using this method offers the option of maintaining an inventory of lenses for immediate dispensing.

Topography-Based Fitting/Design Software This method uses corneal topography in combination with design software to simulate diagnostic fitting. Use of the software eliminates the need for diagnostic lens evaluation. Computer simulation shows the tear layer thickness profile of proposed designs in selected meridians of interest. Note: using this method requires excellent topography that analyzes the largest possible corneal area to most accurately design the ideal lens.

Diagnostic Evaluation After One Night of Wear In this method, a lens from a small diagnostic set with specific parameters is dispensed for fitting characteristics only. These lenses are not designed with the target correction of each patient but are intended only to evaluate the corneal topographic response to one night of wear. After the first night, custom lenses are ordered incorporating the target treatment with any necessary fitting modifications based on corneal topography changes.

In Conclusion

Any of the above methods will allow practitioners to enjoy success with ortho-k. Careful individual evaluation of each process can help them determine with which method they are most comfortable. Talking to colleagues and manufacturers’ consultants can also help practitioners evaluate the pros and cons of each fitting philosophy and the best option for their offices. Success with ortho-k is the destination but, as in life, there is more than one route to get from here to there. CLS