Myopia Control: Ortho-k vs Gas Perms

here's a new journal article discussing "Peripheral Refraction With and Without Contact Lens Correction". it basically compares peripheral refractive error in soft & GP ("hard" or gas permeable lenses). its a bit technical even tho this is just the abstract, but its very interesting. what it says is that gas perms correct peripheral hyperopic refractive error better than soft lenses do. but the super interesting statement is at the end:

"The tradeoff between field curvature and off-axis astigmatism with GP lenses may limit their effectiveness for control of myopia progression."

and what THAT means in English is: while both ortho-k & GP's correct peripheral hyperopic refractive error, GP's likely don't have the same "myopia control" effect as ortho-k lenses do b/c of the GP's tendency to induce oblique, off-axis astigmatism. an interesting finding, for sure:

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Peripheral refractive error degrades the quality of retinal images and has been hypothesized to be a stimulus for the development of refractive error. The purpose of this study was to investigate the changes in refractive error across the horizontal visual field produced by contact lenses (CLs) and to quantify the effect of CLs on peripheral image blur.
A commercial Shack-Hartmann aberrometer measured ocular wavefront aberrations in 5 degrees steps across the central 60 degrees of visual field along the horizontal meridian before and after CLs correction. Wavefront refractions for peripheral lines-of-sight were based on the full elliptical pupil encountered in peripheral measurements. Curvature of field is the change in peripheral spherical equivalent relative to the eye's optical axis.
Hyperopic curvature of field in the naked eye increases with increasing amounts central myopic refractive error as predicted by Atchison (2006). For an eccentricity of E degrees, field curvature is approximately E percent of foveal refractive error. Rigid gas permeable (GP) lenses changed field curvature in the myopic direction twice as much as soft CLs (SCLs). Both of these effects varied with CLs power. For all lens powers, SCL cut the degree of hyperopic field curvature in half whereas GP lenses nearly eliminated field curvature. The benefit of reduced field curvature was partly offset by increased oblique astigmatism. The net reduction of retinal blur because of CLs is approximately constant across the visual field.
The researchers concluded that both SCL and GP lenses reduced the degree of hyperopic field curvature present in myopic eyes, with GP lenses having greater effect. The tradeoff between field curvature and off-axis astigmatism with GP lenses may limit their effectiveness for control of myopia progression. These results suggest that axial growth mechanisms that depend on retinal image quality will be affected more by GP than by SCL lenses.
Shen J, Clark CA, Soni PS, Thibos LN. Peripheral Refraction With and Without Contact Lens Correction. Optom Vis Sci. 2010 Jul 1.

FYI here's the explanation of how ortho-k lenses slow myopia progression:

Negative Image Shell