This study aims at investigating the efficacy of myopic control using ortho-k in younger and older children.

Children wearing ortho-k have been shown to have slower rate of myopic progression than those wearing single-vision spectacles (Cho et al. 2005) or soft lenses (Walline et al. 2009). Younger myopic children (aged 6-10 years old) may have the faster increase in myopia than old myopic children (aged 11-15 years old), i.e. the rate of myopic progression may be different in different age groups and in children with different refractive status (Edwards 1999; Fan et al. 2004; Cheng et al. 2007). Although the refractive correction with ortho-k has been well documented, it is unknown whether the efficiency and reversibility of ortho-k for myopic reduction as well as myopic control are similar in children of different age and refractive groups.

In this 14-month study, the eyeball length in 45 younger (6-10 years old) and 45 older (11-15 years old) myopic children before and after ortho-k will be evaluated. Eyeball elongation will be determined for the first 7 months when single-vision glasses will be prescribed (Phase I) and the next 7 months when ortho-k will be prescribed (Phase I). Rate of myopic progression will be determined and compared between the two groups of children in the two phases.

Inclusion Criteria:

• Age: between 6 to 15 years old
• Myopia: between 1.50D and 4.50D in at least one eye
• Spherical equivalent (SE): between -1.00D to -4.50D in both eyes
• Astigmatism: ≤ 3.00D of axes 180 +/- 30 or ≤ 1.00D of other axes; and the amount is less than refractive sphere
• Anisometropia: ≤ 1.50D in both refractive sphere, refractive cylinder and SE
• Best corrected monocular visual acuity: equal to or better than 0.10 in logMAR scale in both eyes
• Willingness to wear contact lenses or spectacles on a daily basis
• Can obtain good ortho-k results with the study lenses
• Availability for follow-up for at least 14 months

Exclusion Criteria:

• Strabismus at distance or near
• Contraindication for contact lens wear and ortho-k (e.g. limbus to limbus corneal cylinder and dislocated corneal apex
• Systemic or ocular conditions which may affect contact lens wear (e.g. allergy and medication)
• Systemic or ocular conditions which may affect refractive development (e.g. Down syndrome, ptosis)
• Prior experience with the use of rigid lenses (including ortho-k)
• Prior experience with myopia control treatment (e.g. refractive therapy or progressive spectacles)
• Non-compliance to the follow up schedule
• Non-compliance to the use of the prescribed optical correction
• Poor ocular response to ortho-k lens wear
• Significant residual refractive error after ortho-k treatment resulting in poor unaided vision (worse than 0.18 in logMAR scale)

The study started in October 2010 and ended in July 2013. Adverse events during the 33 months were collected and reported

It was a cross-over study in which there was only one Arm/Group. Therefore, the adverse events for the single-vision and orthokeratology phases were combined. The adverse events for each intervention can be found under the second primary outcome in which the results from the two interventions were presented in the two rows

The outcome assessor was responsible for measuring the axial length and was unaware of the intervention (i.e. spectacles or orthokeratology) used by the subjects