The role of outdoor activity in myopia prevention.

Myopia, also known as nearsightedness, is the most common vision disorder among children and young adults. In the last several decades, the prevalence of myopia has surged in East Asia. In some industrialized regions it has already reached an epidemic level (1,2). A smaller increase in the prevalence has also been observed in Western countries (2,3). The cost of visual aids or corrections put a great financial burden on individuals, families and the health care system. Myopia is not just an optical inconvenience. Early onset myopia is often accompanied with fast progression and very likely it will end up with high myopia (higher than 6.00 D myopia). High myopia poses a higher risk for developing glaucoma, retinal detachments and other vision threatening conditions. As our understanding of myopia was and is still poor, the research and development of an effective and safe tool in controlling myopia has been moving forward slowly. The current options for slowing down myopia progression include applying pharmaceutical agents such as atropine, wearing corrections with special optical design including bifocal spectacles, dual-focal contact lenses, and orthokeratology (ortho-K) (4). The most effective treatment up-to-date is 1% atropine, with well-established clinically relevant efficacy. However, the side-effect of long-term use and rebound effect after discontinuation of atropine were major concerns. Recently published results from a study conducted in Singapore clearly showed that atropine at a much lower dosage 0.01% could slow down myopia progression in children though its treatment size was smaller compared to the higher dosage levels: 1.0%, 0.5% and 0.1% (5). In addition, their results indicated that the group with 0.01% atropine had little rebound after cessation of the treatment while the other groups progressed much faster than the control group. More investigations on this promising strategy are still ongoing. Another promising option is ortho-K contact lenses. The benefit of wearing ortho-K in retarding axial elongation has been confirmed by randomized clinical trials (RCTs) (6). Prescribing contact lenses in very young children is still non-conventional due to hygiene and safety concerns. Other optical correction methods include multifocal and bifocal spectacles. Multifocal/bifocal spectacle provides minimal myopia control effect: statistically significant but without clinical significance (4). Finally, none of these intervention methods had been studied for a long period of time (>5 years) and thus their long-term effect is unknown. Unlike studies on retarding myopia progression, publications on myopia prevention methods are rarely seen in literature.