| Purpose. Although orthokeratology (non-surgical corneal reshaping, Corneal Refractive Therapy, CRTRTM) has been used for almost a half century, contemporary CRT's outcomes and mechanisms still require investigation. A series of studies was designed to examine different aspects of non-surgical corneal reshaping for myopic and hyperopic corrections, including the efficacy and stability of this procedure, the effect of the lens material characteristics (Dk/t), and the corneal or superficial structural change (e.g. corneal/epithelial thickness) in corneal reshaping.;Results. In the CRT1 study, after one night of CRT RTM for myopia, the central cornea flattened and the mid-periphery steepened, and myopia reduced. In the CRTH study, after one night of CRT RTM for hyperopia, the central cornea steepened and the para-central region flattened, myopia was induced or hyperopia was reduced, all aberrations except for the astigmatism increased and signed spherical aberration (SA) shifted from positive to negative. In the CRT2 study, after 4 weeks of CRT RTM lens wear, in general, the treatment zones stabilized by day 10, vision improved, myopia diminished, total aberration and defocus decreased and higher order aberrations (HOAs) including coma and SA increased. The visual, optical and subjective parameters became stable by day 10. In the CRTHDK study, after one night of CRTRTM [Menicon Z (MZ) vs. Equalens II (EII)] lens wear, the central corneal curvature and aberration were similar with a slight exception: The mid-peripheral corneal steepening was greater in the EII (lower Dk/t) lens-wearing eyes compared to the MZ (higher Dk/t) eyes. In the STOK study, after brief CRTRTM and CRT RTMH lens wear, significant changes occurred from the 15 minutes time point: The corneal shape and optical performance changed in a predictable way; the central cornea swelled less than the mid-periphery after CRT RTM lens wear, whereas the central cornea swelled more than the para-central region after CRTRTMH lens wear; the central epithelium was thinner than the mid-periphery after CRTRTM lens wear and was thicker than the para-central region after CRTRTM H lens wear.;Conclusion. After one night of lens wear, CRT RTM and CRTHRTM lenses were effective for myopia and hyperopia correction, respectively. In the 4 week CRTRTM study, the treatment zone changed during the first 10 days. Its size was associated with VA, refractive error, aberrations, and subjective vision. In the CRTHDK study, after one night of lens wear, changes in corneal shape were slightly different, with more mid-peripheral steepening in the lower Dk lens-wearing eyes compared to the higher Dk lens-wearing eyes. Changes in central corneal shape and optical performance were similar in both eyes. In the STOK study, CRTRTM lenses for myopia and hyperopia induced significant structural and optical changes in as little as 15 minutes. The cornea, particularly the epithelium, is remarkably moldable, with very rapid steepening and flattening possible in a small amount of time.;*Please refer to dissertation for table.;Methods. Details are in the following summary Table A-1.*. |
