The Effect of Lens Design on Corneal Power Distribution in Orthokeratology

Abstract

SIGNIFICANCE: This study will enhance our understanding of the effects of orthokeratology lens design on corneal profile, the results of which may be useful in developing future orthokeratology lens designs.PURPOSE: This study aimed to evaluate the effect of lens design on corneal power distribution after orthokeratology using mathematical methods.METHODS: Sixty-five subjects were enrolled in this prospective study and assigned to four groups: Euclid with 6.2-mm back optic zone diameter (aged <14 years), Euclid with 6.2-mm back optic zone diameter (aged ≥14 years), double tear reservoir lens with 5.0-mm back optic zone diameter, and double tear reservoir lens with 6.0-mm back optic zone diameter. Manifest refraction and corneal topography were checked at baseline and 1 day, 1 week, 2 weeks, and 1 month after lens wear. Relative corneal refractive power change was calculated by a polynomial function and a monomial function. The maximum relative corneal refractive power change (Y max ) and the corresponding distance from the corneal center (X max ) were analyzed. Relative corneal refractive power change over time and between groups was compared using repeated-measures analysis of variance. RESULTS:Refractive reduction and central corneal flattening were seen at all follow-up visits after orthokeratology lens wear, being fastest in the 5.0-mm back optic zone diameter group ( P < .001). The cornea steepened in an aspheric way toward the midperiphery and peaked at approximately 2 to 3 mm off the apex. Overall, Y max was not different among the four groups, but X max was smallest in the 5.0-mm back optic zone diameter group ( P < .001). At 1/2 X max , relative corneal refractive power change of the 5.0-mm back optic zone diameter design was significantly higher than that of the other three groups ( P < .001). The power exponent of the monomial of the 5.0-mm back optic zone diameter design was greater than that of the other three groups ( P < .001).CONCLUSIONS: An orthokeratology lens design with smaller back optic zone diameter might yield a faster myopic reduction and a smaller aspheric treatment zone.

Investigation of the relationship between contact lens design parameters and refractive changes in Ortho-K

“…For example, some studies have investigated the relationship between smaller TZ and greater peripheral power change ( Pauné et al., 2021 ; Zhang et al., 2022 ), suggesting a smaller BOZ leads to a greater peripheral corneal power change. Others have examined the effect on myopia control outcomes of decentration of the TZ ( Chen et al., 2018 ; Gu et al., 2019 ; Wang and Yang, 2019 ).…”

Study on Related Factors of the Treatment Zone After Wearing Paragon CRT and Euclid Orthokeratology Lenses

“…In the study by Guo et al, 20 Zhang et al, 17 and Paune et al, 24 a smaller treatment zone was obtained by reducing the BOZD of VST orthokeratology, and the results showed that the axial length of patients wearing smaller BOZD lenses grew slower. Zhang et al 35 also found that the smaller treatment zone of VST-designed and CRT-designed orthokeratology can slow down the axial growth of myopic children.…”

“…After wearing orthokeratology, a relatively flat area is formed in the center of the front surface of the cornea under the pressure of the lens base curve, which is called the treatment zone. 15 Carracedo et al 16 and Zhang et al 17 showed that wearing the orthokeratology with a smaller back optic zone diameter (BOZD) produced a smaller treatment zone diameter (TZD). The TZD is influenced not only by the design of the lens itself but also by certain biometric factors.…”

Modeling and Prediction of the Immediate and Short-Term Effect of Myopic Orthokeratology

“…3,19,20 Related to this, lens design can influence changes in epithelial thickness because of different sizes of treatment zones and number of lens curves. Zhang et al 21 showed that lenses with a smaller back optic zone diameter yielded a faster myopic reduction and a smaller aspheric treatment zone.…”