Abstract: Orthokeratology (Ortho-K) lenses have been widely used for myopia correction and control in children and adolescents due to their ability to provide clear uncorrected visual acuity and effective myopia suppression. Small optical zone Ortho-K lenses refer to designs with an optical zone diameter smaller than 6.0 mm, typically featuring specifications such as 5.0 mm or 5.5 mm optical zones. Compared to conventional Ortho-K lenses with larger optical zones, small optical zone lenses induce a smaller central treatment zone and a steeper mid-peripheral defocus ring. This design generates more pronounced peripheral retinal myopic defocus and higher-order aberrations, thereby enhancing myopia control efficacy. However, such optical characteristics may lead to reduced objective visual quality parameters, such as the modulation transfer function (MTF).

Key words: Orthokeratology lens, Optical zone size, Myopia control, Visual quality