The goal of this non-inferiority randomized clinical trial is to compare the myopia control efficacy of Ortho-K lenses (OKL) and Defocus (DIMS) spectacles in myopic children aged 6-12 years. The main question it aims to answer is:

- Is the DIMS spectacle lens not worse than the OKL after 18 months of therapy?

The participants are randomly assigned to either OKL or DIMS spectacles and followed during 18 months of therapy.

Inclusion criteria:

- Myopic children aged 6 to 12 years: Myopia of the 6 to 8-year-olds (inclusive): -1.00 to -4.75 D spherical component and up to -2.50 D of regular astigmatism (both eyes).

Myopia of the 9 to 12-year-olds (inclusive): -2.00 to -4.75 D spherical component and up to -2.50 D of regular astigmatism (both eyes).

• Anisometropia ≤ 1.50 D cycloplegic spherical equivalent refractive error.
• Best corrected visual acuity at age 6 to 12 years (inclusive): 0.8 Snellen (equivalent to ≥ 3/5 letter on the 0.8 line = 78 ETDRS letters)

Exclusion criteria:

• Manifest or intermittent squint.
• Contraindications to the use of OKL comprising (not exhaustive): keratoconus, chronic allergic conjunctivitis and keratoconjunctivitis sicca.
• Previous eye surgery.
• Chronic eye disease demanding daily use of eye drops.
• Non-compliance to eye examinations (unstable fixation or anxiety towards contact lenses).
• Previous myopia control treatment.