Reshaping Your Practice Success
BY ROBERT ENSLEY, OD, & EDWARD S. BENNETT, OD, MSED, FAAO
There has been a resurgence of interest in corneal reshaping or overnight orthokeratology (OOK). Rigid lenses were first thought to play a role in slowing myopia progression decades ago, when flat-fitting polymethyl methacrylate (PMMA) lenses were shown to flatten corneal curvature (Morrison, 1956). Through the 1980s, studies showed temporarily corrected myopia when these rigid lenses were removed, but safety and efficacy concerns prevented widespread usage (Kerns, 1978; Binder et al, 1980; Polse et al, 1983).
With the development of GP materials and reverse geometry lens designs, the first overnight corneal reshaping lenses were approved by the United States Food and Drug Administration (FDA) in 2002. Recent studies indicate that the peripheral hyperopic defocus created by modern corneal reshaping designs reduces the stimulus to eye growth (Smith, 1998; Smith, 2009).
Although most new corneal reshaping patients are under the age of 18, don’t restrict the use of these lenses to young myopes. OOK is a viable option for any myope seeking temporary visual correction without having to wear glasses or contact lenses during waking hours. This may include athletes, most notably in water sports, or occupations such as firefighters or pilots for whom lens wear may become uncomfortable. Adults experiencing awareness with their lenses and who desire to be free of spectacles may also be candidates for OOK. This includes presbyopes if they are suitable for monovision or are willing to wear reading glasses.
For optimal results, corneal reshaping requires a level of commitment to the fitting process and compliance with lens wear. The FDA approval includes correction of up to –6.00D of myopia and –1.75D of with-the-rule astigmatism. Success with prescriptions outside of this range has been demonstrated anecdotally; however, patients must be notified of off-label use.
The pre-fitting examination should include refraction, keratometry, baseline corneal topography, and an ocular health assessment. Immediately rule out patients who have corneal irregularity or disease. While lenses can be fit diagnostically, empirical fitting with refraction and keratometry readings may be more efficient. If potential patients are highly myopic, hyperopic, presbyopic, or have unrealistic expectations, a staff member can address this over the phone.
Corneal topography is essential. In addition to troubleshooting, the baseline topography can yield valuable information. Axial maps indicate whether corneal astigmatism is apical or limbus-to-limbus. Patients who have limbus-to-limbus or lenticular astigmatism may not be ideal candidates. Topography can also show eccentricity or shape factor. Greater eccentricity can predict increased potential for myopia reduction (Mountford, 1997). Although topography is typically measured in photopic settings, it also can provide pupil diameter. If the scotopic pupil is greater than 5mm, warn the patient about glare or halos at night.
The FDA has approved two systems for corneal reshaping: Paragon Corneal Refractive Therapy (CRT) and Bausch + Lomb Vision Shaping Treatment (VST). You must be certified to fit either system. Check out www.bausch.com/en/ecp/our-products/orthokeratology/vision-shaping-treatment-online-certification (for VST) and www.paragoncrt.com/getcertified (for Paragon CRT). Remember that corneal reshaping applications extend beyond just myopia control. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #222.
Dr. Ensley is currently the cornea and contact lens resident at the University of Missouri-St. Louis College of Optometry. Dr. Bennett is assistant dean for Student Services and Alumni Relations at the University of Missouri-St. Louis College of Optometry and is executive director of the GP Lens Institute. You can reach him at email@example.com.