Myopia is the most common eye disorder in the world. It is estimated that 4.8 billion people (49.8% of the world’s population) will be myopic by 2050 (Holden et al, 2016). Developed Asian countries are particularly affected. For example, in Singapore and Taiwan, up to 84% of school-aged children are myopic (Wu et al, 2016). In contrast, but still of concern, about 50% of adults in the United States and Europe are myopic. High myopia is a leading cause of blindness and is associated with comorbidities, such as retinal detachment, macular choroidal degeneration, premature cataract, and glaucoma (Cho et al, 2016). Pediatric onset is most troublesome since this leaves more time for progression to higher myopia. Preventing children from developing myopia and its associated visual impairments is, therefore, crucial.
Either preventing the onset or limiting the progression of myopia is considered myopia control. Effective approaches for limiting the progression include antimuscarinic agents, such as atropine, orthokeratology (ortho-k), and soft bifocal contact lenses (Walline, 2016). Nevertheless, all myopia control strategies are off-label. Myopia control with contact lenses is accomplished by providing a myopic blur cue to the retina, which is assumed to act as a retinal cue to slow myopic eye growth (Walline, 2016).
Orthokeratology: Ortho-k uses GP lenses worn overnight to temporarily reshape the cornea to correct for refractive error during waking hours (Figure 1). Myopic orthokeratology shifts the cornea from its normal prolate aspheric shape toward an oblate asphere (Rinehart, 2006) (Figure 2). When reshaped, the central apex is flatter than the midperipheral cornea creating the needed distance correction and the peripheral defocus cue. On average, ortho-k slows myopic progression by 43% (Walline, 2016).
Soft Bifocal Lenses: Soft bifocal contact lenses come in both center-distance and center-near designs. Most commercially available molded soft bifocal lenses are center-near designs, however, there are more myopia control studies using center distance bifocals. On average, soft bifocal contact lenses slow myopic progression by 46% (Walline, 2016).
Other Contact Lens Options: GP lenses effectively correct high amounts of myopia and astigmatism. Bifocal GP lenses are, therefore, better suited for myopia control in children with high amounts of refractive error who are difficult to correct with ortho-k or soft bifocal lenses (Liu, 2017). Many corneal and scleral GP lenses are commercially available in bifocal designs. Hybrid lenses also are available with bifocal parameters.
The prevalence of myopia is increasing worldwide. High myopia is best prevented and myopia control offers a solution. Early intervention is best and contact lens based interventions aim to create a peripheral defocus retinal cue that slows myopic progression. Management may involve ortho-k or bifocal contact lenses including soft or GP varieties as the situation warrants. CLS
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