The aim of the proposed study is to investigate the predictive value of corneal biomechanical properties in corneal reshaping therapy and the role of these parameters in determining the amount of myopia reduction.

Experiment 1: To evaluate changes in corneal biomechanics caused by short-term corneal reshaping therapy.

Subjects will wear a conventional RGP lens in one eye, randomly selected, and an orthokeratology lens in the fellow eye, for 30 minutes, 60 minutes and one night, respectively. Corneal stiffness and tangent modulus will be measured before and after each wearing period.

Experiment 2: To evaluate changes in and the recovery of corneal biomechanics effected by long-term corneal reshaping and to assess whether corneal biomechanics can predict the rate of corneal reshaping.

Subjects will wear orthokeratology lenses for 6 months. Regular follow up visits (1 week, 1 month, 3 months and 6 months) will be arranged to monitor the changes in corneal stiffness and tangent modulus.

Inclusion Criteria:

• Myopia between -4D to -5D, with-the-rule astigmatism not more than 1.5D, spherical equivalent between -4D to -5.75D, difference between two eyes within 1D, best corrected spectacle visual acuity 0.10 logMAR in each eye

Exclusion Criteria:

• previous corneal reshaping therapy, long-term contact lens wear, ocular disease

6 months