Defocus Spectacle Lenses for Myopia Control

Myopia is a refractive error of significant global public health concern and is primarily caused by an increase in the axial length of the eye. Myopia is considered a growing “global epidemic” due the rising prevalence of myopia worldwide. Myopia affects 85 to 90% of young adults in Asian countries such as Singapore and Taiwan, and said to affect approximately 25 to 50% of adults in the United States and Europe.¹ Myopia can be classified as low (when less than -3D), moderate (between -3D and -5D) and high (worse than -5D). According to Holden et al, in 2000 approximately 1,406 million people had myopia (23% of the population) and nearly 163 million people with high myopia (< -5D), (2.7% of the population). By 2050, projections estimate 4,758 million people with myopia (49.8% of the population) and 938 million people with high myopia (< -5D), (9.8% of the population), amounting to nearly 5 billion people with myopia worldwide.⁶ Myopia carries a high risk of complications such as retinal detachment, myopic macular degeneration, early-onset cataracts, and glaucoma that are linked to the severity of myopia. Unfortunately, general population is not aware of myopia in children and its risks.³ In children with high myopia, it is important to investigate the possibility of syndromic myopia. Early detection of myopia onset and its progression is crucial for effective myopia control strategies.

The challenge is to prevent the onset of myopia and on the other hand, to reduce or slow down its progression once it is already present. To prevent or delay onset of myopia, environmental measures such as increasing outdoor time reducing near work including screen time and early bedtime should be adopted. Nowadays, in eyes that are already myopic and progressing, we finally have efficient techniques at our disposal to control progression. ^{8, 9} Defocus corrective spectacle lenses and defocus contact lenses aim to reduce hyperopic defocus observed in myopic eyes at the mid peripheral to peripheral retina and therefore slow myopia. Orthokeratology remodels the cornea and the remodeled shape is considered to reduce peripheral hyperopic defocus. Low-dose atropine also slows myopia but the exact mechanism i.e., whether it acts via muscarinic receptors or on scleral collagen remains unknown. Since a myopic eye needs to be corrected to restore sight, of the various options, defocus corrective spectacle lenses which correct as well as slow myopia, appear to be a simple and convenient treatment option to apply in children. Although there are many different defocus spectacle lenses available with varying designs and concepts, however we need to focus only on systems that are supported by evidence from robust clinical studies.
 

In conclusion, the most promising treatments to manage and slow myopia include environmental measures, defocus corrective spectacle lenses, defocus contact lenses, orthokeratology, and low-dose atropine pharmacological treatments. Defocus corrective spectacle glasses are an easy and convenient way to treat children with myopia, as corrective lenses such as spectacles are needed anyway to correct myopia and restore vision. If the progression continues, there are options to combine defocus spectacle glasses and low-dose atropine to avoid an evolution to high myopia.