You may have heard or read about the growing prevalence of myopia during the last few decades, especially among children and teenagers. While myopia has reached epidemic proportions in parts of Asia, the National Eye Institute warns myopia will impact 39 million Americans by 2020 and 44.5 million by 2050. Myopia occurs when the eyeball is too long from front to back, or the cornea (clear front cover of the eye) is steeply curved. Moderate cases of myopia generally do not result in serious repercussions.
Progressive myopia is particularly worrisome because it can lead to an increased risk of myopic degeneration, retinal detachments, glaucoma, lacquer cracks, and posterior staphylomas (abnormal protrusion of uveal tissue in the back of the eye). High myopia (also called pathological myopia) is generally defined as a refractive error exceeding -6.00 diopters and/or an axial length longer than 26.5 mm.
Myopia Risk Factors in Children
Several myopia studies have yielded insights regarding risk factors, some of which are preventable. A recent Indian study found longer hours of reading-writing, use of computers/video games, and watching television were significant risk factors for progression of myopia. Conversely, a minimum of 2 hours a day spent outdoors reduced the risk of myopia progression. A competitive educational environment, long study hours, and reduced outdoor activity are common among many schoolchildren in Asia and some Western countries.
The American Academy of Ophthalmology lists the following risk factors.
- Near work or visual activity with a high accommodative demand
- High level of educational attainment
- Low levels of outdoor activity
- Computer games
- Electronic devices
- Female gender
- Season of birth/daylight hours
- Parental myopia
- Use of a night light
- Younger age at diagnosis
- High IQ score
Preventing Myopia in Children
Multiple studies have shown time spent outdoors can reduce the likelihood of myopia development and progression. In a 2-year Australian study, researchers concluded 12-year-old children who spent more time outdoors had less myopia at the end of the study period than others, even after adjusting for hours of reading performed, parental myopia, and ethnicity. A Taiwan study showed similar results, showing after a year, children who spent time outside during recess had a significantly lower onset of new myopia than children who were not encouraged to engage in outdoor activities during recess (8.4% vs. 17.6%). So if you notice your children are spending hours on end reading, watching television, using electronic devices, or playing computer games, encourage them to go outside more often (weather permitting).
The Role of Oxidative Stress
A strong body of evidence suggests oxidative stress within the eye is the primary reason for vision breakdown, the development of myopia, and potential complications including cataracts, retinal tears, and macular degeneration. A majority of oxidative stress is associated with increased amounts of reactive oxygen species (ROS) in the eye, especially the retina. The retina is exposed to continual light exposure, contributing to high amounts of ROS. The speed at which oxidative stress damages the eye is tied to the status of key elements including dopamine, nitric oxide, and several nutrients.
The brain neurotransmitter dopamine plays a direct role in vision, controlling critical eye growth in infancy and childhood. Researchers believe when the eye is still maturing during childhood, if dopamine isn’t dispersed adequately into the retina, the eye becomes elongated, resulting in strained convergence, focus, and the development of myopia. Moreover, dopamine interacts with the neurochemical nitric oxide within the eye. Nitric oxide works with nitric oxide synthase, which regulates eye growth, modulates nerve activity within the eye, relaxes eye muscles, and widens blood vessels.
Many of the same antioxidants that stop the progression of age-related eye disease, also play an important role in myopia prevention because they combat oxidative stress. Therefore it is crucial children eat a healthy, balanced diet rich in vitamins A, C and E, beta carotene, and zinc/copper. Zinc is especially critical for the retina, therefore a deficiency can increase the possibility of damage to the DNA, proteins, lipids, and connective tissues of the eye. This can lead to a higher risk of vision changes, progressive myopia, and eye diseases in adulthood. Lean beef, pork, chicken, and turkey (both dark and breast meat), seafood, eggs, wheat germ, mixed nuts, black-eyed peas, kidney beans, lentils, and tofu are great sources of zinc.
If you suspect your child is at risk, schedule a visit with an eye doctor as soon as possible. Early detection and correction is the best way to prevent your child from becoming part of the myopia epidemic.