Effectiveness of Orthokeratology in Myopia Control

Myopia

The high prevalence of myopia - especially in Asian countries - is well documented, as are the sight-threatening complications of high or degenerative myopia. Retinal detachment, glaucoma, vitreal degeneration and focal retinal changes may occur secondary to the progressive axial elongation of the eye with age. Specialty rigid lenses have long been shown to lessen this progression in the pediatric population; orthokeratology (ortho-k) lenses are worn at night and change the corneal topography to correct low to moderate amounts of myopia. Most of the studies on orthokeratology were conducted on Asian children. To the best of the investigators knowledge, no study has been done on African American (AA) children. The investigators' project seeks to investigate the efficacy of ortho-k in slowing axial elongation and myopic progression in AA children compared to that in other races.

Orthokeratology (ortho-k), when used for partial or full correction of myopia, has been shown to slow myopic progression in children by 36-56% as compared to their spectacle or contact-lens wearing peers.1 This effect is achieved by limiting the axial elongation of the eye,1, 2,3, 4 which is of particular concern in high myopes (\>6.00D) and children, where myopic progression has been shown to proceed at a faster rate than average.1 As early intervention is considered beneficial if not essential, Ortho-k as a treatment modality for diminishing myopic progression has, to our knowledge, been studied mostly in Asian children. The safety and efficacy of ortho-k as a means of decreasing myopic progression was well established by the Children's Overnight Orthokeratology Investigation (COOKI), who evaluated refractive error, visual changes and ocular health over a period of 6 months in myopic children. 7 The Longitudinal Orthokeratology Research in Children (LORIC) study looked at axial elongation in children as old as 12 years, and found that ortho-k decreased axial elongation by approximately 50% compared to be-spectacled controls. 2 They also noted, however, high variability amongst the children that limits the clinician's ability to predict the outcome of the intervention.2 The Corneal Reshaping and Yearly Observation of Myopia (CRAYON) study confirmed that patients fit with ortho-k lenses showed less change in axial length and vitreous chamber depth when compared to subjects wearing soft contact lenses. 3 Other more recent studies by Santodomingo-Rubido et al, 7 Kakita et al4 and Charm et al1 confirm this decrease in axial elongation using IOL Master measurements. The most commonly accepted theory on how orthokeratology decreases axial elongation relies on the peripheral defocus created on the retina by the corneal changes made by the rigid lens. 9 Hoogerheide et al showed that those at greatest risk for myopic progression were those whose peripheral refraction was hypermetropic10 - that is, they had a hyperopic peripheral 'defocus'. A number of studies have since suggested that treatment approaches to myopia correction should address this peripheral refraction as a means of slowing further axial elongation.9 When looking at subjects treated with ortho k, we see that the lenses do in fact introduce a peripheral myopic defocus while leaving the central refraction more or less emmetropic. 9 With this study, the investigators hope to expand potential application of orthokeratology to a novel population, AA children.

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