Abstract
Purpose :
To monitor recovery of corneal hysteresis (CH), corneal resistance factor (CRF), and tangent modulus (E) after long-term overnight orthokeratology
Methods :
Thirty-seven young Chinese subjects (age, 18-27 years) were fitted with overnight orthokeratology lenses using super high gas permeable material (Menicon Z Night with Dk 163×10-11). Data of one eye of each subject was selected for analysis. Their baseline refractive sphere was -4.44 +/- 0.35D, refractive astigmatism was -0.50 +/- 0.33D. CH and CRF were obtained using the Ocular Response Analyzer, and E was obtained from corneal indentation (Figure 1). Corneal biomechanics (CH, CRF, and E) was measured at baseline, after 6 months of lens wear, then at 1 week and 1 month after cessation of lens wear.
Results :
Mean refractive sphere reduced to 0.11 +/- 0.57D, and astigmatism changed to -0.74 +/- 0.34D after six months of overnight orthokeratology. Median CH decreased significantly from 10.40mmHg (interquartile range 1.50mmHg) at baseline to 9.57mmHg (1.80mmHg) at 6-month (post hoc, p = ); correspondingly mean CRF decreased significantly from 9.95 +/- 1.30mmHg to 9.08 +/- 1.16mmHg (post hoc, p = ). After cessation of lens wear for one month, refractive sphere and astigmatism returned to -4.16 +/- 0.42D and -0.57 +/- 0.38D, respectively. Correspondingly, median CH returned to baseline level of 10.13mmHg (1.37mmHg) (post hoc p = ), while CRF was still significantly lower (9.46 +/- 1.29mmHg) (post hoc p = ). Corneal tangent modulus was a stable parameter throughout the study, from 0.536 +/- 0.118MPa at baseline, to 0.571 +/- 0.106MPa after 6 months of overnight orthokeratology, back to 0.539 +/- 0.101MPa after cessation of lens wear for one month (Figure 2).
Conclusions :
Both corneal hysteresis and corneal resistance factor demonstrated significant decrease from overnight orthokeratology. CH returned to baseline level after cessation of lens wear while CRF was still low. Corneal tangent modulus was a stable corneal biomechanics parameter from overnight orthokeratology.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.