Article Date: 9/1/2004

orthokeratology today
Astigmatism and Ortho-K
BY JOHN MOUNTFORD, DIP. APP. SC, FAAO, FCLSA

An anti-ortho-k academic once told me that ortho-k would always be anecdotal until it could correct astigmatism. The published papers of the traditional methods showed an increase in with-the-rule astigmatism because of superior lens decentration, which still occurs today with poorly fitted lenses, and an inability to correct against-the-rule astigmatism, which is also true today.

Figure 1. Pattern of astigmatic RGL.

Eureka!

The correction of astigmatism in ortho-k means two things:

Swiss OD Michael Baertschi and his colleagues are the first group in the world to publish topography-validated results on the correction of corneal and residual astigmatism with ortho-k. The concept behind this breakthrough was that the fluid forces acting in the steep meridian were different than those acting in the flat meridian, and they altered the lens design to bring about the desired result. Dr. Baertschi presented his preliminary failures at the Global Orthokeratology Symposium, but kept working on the problem. The following topography results and refractive changes speak for themselves.

Figure 2. Note the change in corneal shape.

Proof Positive

Figure 1 shows the fluorescein pattern of an astigmatic reverse geometry lens (RGL). It's not a bitoric lens in the true sense of the word because the relationship between the flat and steep meridian is variable. The reverse curves are also variable and, unlike a true bitoric, don't have a constant relationship to the base curves. Note the difference in tear layer thickness between the meridians and the oval central "touch" area.

Figure 2 shows the change in corneal shape over a period of time. The ability to "push" the astigmatism outside the pupil zone is what makes this design superior to spherical lenses. The original prescription for this patient was ­1.75/­2.00 @ 180. The final prescription was +0.25D sph (20/15). Figure 3 shows a dramatic change from ­3.75/­3.00 @ 8 to +0.25/­0.50 @ 8.

Figure 3. Dramatic change (from ­3.75/­3.00 @ 8 to +0.25/­0.50 @ 8.

Leading Us to Believe

Dr. Baertschi and his colleagues have shown us that the application of science and technology as well as good old-fashioned original thinking and innovation to a complex problem results in a successful outcome for our patients. The correction of astigmatism with ortho-k is an awesome breakthrough -- these individuals deserve our heartfelt congratulations.

 

Dr. Mountford is an optometrist in private practice specializing in advanced contact lenses for keratoconus, post refractive surgery and pediatric aphakia. He is a visiting contact lens lecturer to QUT and UNSW, Australia.

 


Contact Lens Spectrum, Issue: September 2004