This is a 24-month longitudinal randomized controlled trial aiming to evaluate the effectiveness of myopia control by Breath-O correct orthokeratology lenses in different myopia progression groups classified according to their initial electro-retinal responses.

Myopia is the most common refractive error in the world. In Hong Kong, the number of children in myopia is on the rise and approximately 80% of children are myopic by the end of childhood. Orthokeratology is one of the most successful myopia control methods adopting the strategy of peripheral defocus, in which the natural emmetropization process is harnessed by the myopic defocus induced by the orthokeratology lenses.Currently, Breath-O correct lenses are new designed ready-made orthokeratology lenses which are made of new material with higher elasticity as compared traditional lens material.

A recent study has shown young children with an initial weakened central electrical signal from the inner retina had faster myopia progression as measured by multifocal electroretinogram(ERG). We will classify the slow and fast progression group based on the ERG results, so as to evaluate the clinical effectiveness of the newly designed lenses in controlling myopia in children with different rates of progression.

Inclusion Criteria:

• Refractive error: Spherical: -1.00D to -4.00D; Cylindrical: half of Sph (against-the-rule Astig.: less than -0.75D)
• Best corrected Visual acuity: monocular ETDRS 0.1 or better

Exclusion Criteria:

• Ocular abnormality
• Contra-indicated for overnight orthokeratology lens wear
• History of refractive surgery
• Systemic diseases
• History of orthokeratology lenses wearing or other myopia control methods