Purpose. To investigate the corneal shape and optical performance following one night of Corneal Refractive Therapy for hyperopia (CRTH®).
Methods. Twenty subjects (spherical equivalent: −2.14 ± 2.54 D) were fit with a Paragon CRTH® lens (Dk = 100) on one eye randomly. The other eye served as the control. Aberrations, refractive error, and corneal topography at various locations along the horizontal meridian were measured at baseline prior to lens insertion, and immediately after lens removal and at 1, 3, 6, 12, and 28 hours later. Root mean square wavefront errors were measured using a 4.5 mm pupil size.
Results. After one night of CRTH® lens wear, the central cornea steepened and paracentral region flattened in the experimental eyes (p < 0.001), whereas no significant location effect was found in the control eyes (p = 0.139). Refractive error (mean ± SE) changed by 1.23 ± 0.21 D (p < 0.001). The defocus increased by 0.58 ± 0.09 μm (p < 0.001). Higher-order aberrations, coma, and spherical aberrations increased by factors of 2.69, 2.58, and 4.07, respectively (all p < 0.001). Spherical aberrations shifted from positive to negative. Astigmatism did not change over time (p = 0.771). All parameters returned to baseline by 28 hours (all p ≥ 0.808). Aberrations and refractive error did not change in the control eyes (all p ≥ 0.082).
Conclusions. The CRTH® lens steepens the central cornea and flattens the paracentral region, which alters the ametropia by inducing a myopic shift. It appears to be effective for correcting hyperopia and also is reversible.
CIBA Vision® Corporation, Atlanta, Georgia (FL) and Centre for Contact Lens Research, School of Optometry, University of Waterloo, Waterloo, Ontario, Canada (LS, TS, DF)
Received March 10, 2006; accepted August 1, 2006.