The two-year prospective study aims at investigating the benefits of frequent replacement (monthly) orthokeratology lenses in myopia control in terms of effectiveness in control and prevention of ocular complications. The secondary objective will be investigating the use of weekly protein removal system in monthly replacement modality orthokeratology lenses on surface deposit.

This is a two-year randomized trial. Existing orthokeratology lens wearers (aged 8-13 years), who have completed a 2-year myopia control using orthokeratology, will be recruited and monitored for another two years. Eligible subjects will be randomly assigned to monthly or yearly replacement modality. Axial elongation and ocular conditions will be compared between the monthly and yearly replacement groups.

Subjects on monthly replacement lenses will be randomly assigned to normal cleaning and intensive cleaning groups. Subjects in normal cleaning group will be provided with complimentary contact lenses solutions for daily cleaning and disinfection. In addition to the daily procedures for lens case, subjects in the intensive cleaning group will be required to perform weekly protein removal. All subjects on yearly replacement lenses will be required to performed intensive cleaning such that they will follow normal daily cleaning and disinfection as well as weekly protein removal.

Inclusion Criteria:

• Aged 8-15 years
• Have completed a two-year myopia control study using ortho-k
• Normal ocular and general condition and not on medication which may contraindicate ortho-k lens wear
• Pre-ortho-k refractive sphere between -0.75 to -4.00 DS, refractive cylinder ≤ -1.50 DC and anisometropia ≤ -1.00 D
• Best correctable vision better than 0.08 logMAR in the worse eye
• Normal binocular function and accommodative status

Exclusion Criteria:

• Strabismus at distance or near
• Contraindication for ortho-k lens wear
• Prior history of ocular surgery, trauma, or chronic ocular disease
• Systemic or ocular conditions that may interfere refractive development
• Systemic or ocular conditions that may interfere tear quality and contact lens wear
• Poor response to the use of study lenses
• Poor compliance to test procedures
• Poor compliance to the use of ortho-k lenses (e.g. use of solution, use of lenses)
• Poor compliance to follow-up schedule

The outcome assessor was responsible for measuring the axial length and was unaware of the replacement modality of intervention used by the subjects. Another independent examiner will be responsible for grading surface coating from the images taken without disclosure of the information on the cleaning procedures.