The prevalence of myopia is increasing in the U.S. and worldwide. Researchers project the trend will continue in the coming years. Also known as nearsightedness, myopia occurs when the eye grows too long from the cornea to the retina. Instead of focusing images on the retina, images are focused at a point in front of the retina. As a result, people with myopia have good near vision but poor distance vision. Almost 42 percent of Americans are nearsighted, up from 25 percent in 1971. In the developed countries of East and Southeast Asia, the prevalence has now reached 80 to 90 percent among children in high school. Projections suggest that almost 50 percent of the world will be myopic by 2050.
Also on the rise is high myopia, also known as pathologic myopia, a condition that increases the risk of retinal detachment, glaucoma, and the early development of cataracts. While simple myopia is correctable with glasses and contact lenses, pathological myopia is one of the leading causes of visual impairment and blindness. Whereas the prevalence of high myopia is about 4 percent in the U.S., in East and Southeast Asia, about 20 percent of children completing high school have high myopia and are now at high risk of uncorrectable vision loss.
Although genetics play a role in myopia, the sudden increase points to environmental factors. Several studies have shown a link between near work and myopia in children.
Researchers in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) study which followed eye development of more than 1,200 children, ages 6 to 14, found that children who spent more time outdoors had a smaller chance of becoming nearsighted. The researchers also showed that time spent outside is independent from time spent reading, contradicting the assumption that less time outside means more time doing close work. Researchers are unsure why time outdoors helps prevent the onset of myopia. Spending time outdoors does not appear to slow myopic progression once myopia has set in.
Eyes grow quickly in infancy, slow down at school age, and reach adult size by late teens. During this long growth period, also known as emmetropization, the development of the eye is a highly regulated process. As eyes grow, the curvature of the lens and the length of the eye must coordinate to maintain focus on the retina. There is some mechanism, not clearly understood at this time, that interferes with normal emmetropization that allows the eye to get longer and cause myopic blur.
The best prevention for myopia in children is more time outdoors. Even small amounts of increased time outdoors will delay the onset of myopia and may reduce the severity of myopia resulting in less pathological myopia.
Low concentration (0.01%) atropine eye drops administered daily have been shown to be effective for preventing the onset of myopia without significant side effects. It appears higher dosages of atropine may be more effective, but side effects are increased as well.
Children wearing multifocal contact lenses had slower progression of their myopia, according to results from a clinical trial funded by the National Eye Institute, part of the National Institutes of Health. Shaped like a bullseye, the soft multifocal contact lenses have two basic portions for focusing light. The center portion of the lens corrects nearsightedness so that distance vision is clear, and it focuses light directly on the retina. The outer portion of the lens adds focusing power to bring the peripheral light rays into focus in front of the retina. Animal studies show that bringing light to focus in front of the retina cues the eye to slow growth. The higher the power added, the further in front of the retina it focuses peripheral light.
Other studies have shown promise for orthokeratology (ortho-k) contact lenses, which work by reshaping patient's corneas at night while they sleep. Users remove the lenses during the day. Ortho-k lenses change the shape of the cornea to focus peripheral light to a point in front of the retina, working in the same way as the bifocal lenses do. While the mechanism is not completely understood, ortho-k contact lenses seem to be one the more effective ways to control myopic progression in children.
Researchers still need more information about the exact nature of myopic progression and the methods that can be used to mitigate its prevalence and severity. Studies are continuing and protocols are being revised to provide better outcomes for children. It is recommended that children have annual eye exams to screen for myopia and intervene as early as possible to prevent myopic progression. Myopia investigators have developed a screening questionnaire that may help parents asses the risk their child may have in developing myopia. Click here to take the assessment.