Myopia, also called nearsightedness or shortsightedness, is caused by a combination of genetics and environment. The genetic component is more important in the more severe pathological myopias of very high powers (arbitrarily over a -10.00) while the environment is more important in the much more common myopia that often starts during the school years.
Current research is showing two main methods of slowing or stopping myopic progression: Control of peripheral hyperopia and increased outdoor time.
Peripheral HyperopiaEyes that are in-focus centrally, whether naturally or with normal contact lenses or glasses, often have a different focus peripherally. Peripheral hyperopia, where the image is focused behind the peripheral retina, results in myopic progression. The opposite is also true: peripheral myopia is protective against myopic progression. The mechanism of action is telling the eyeball to either grow longer or stop growing.
These feedback systems (hyperopia = grow longer, myopia = stop growing) are active during the process of emmetropization which allows an infant's eye to stay in focus as it matures and grows significantly. The control is almost totally within the retina such that the retina can detect whether it is out of focus due to too strong a focus (myopia) or too weak (hyperopia) and respond by chemical signals to either grow or stop growing.
Creation of peripheral myopia is being investigated in many areas as a method to control myopic progression. Contact lens companies are creating lenses similar to bifocal contact lenses that create a peripheral myopia in a complete circle around central vision. Spectacle lens companies are experimenting with the same thing for glasses. OrthoK or Orthokeratology lenses mold the same peripheral myopia onto the cornea each night, providing vision during the day without glasses or contact lenses.
Standard glasses do not create peripheral myopia and in fact generally create more peripheral hyperopia, thus presumably making the myopia progress faster. Undercorrection, a common attempt to slow myopia, has been shown in studies to actually make myopia worse, an unexplained finding but probably related to not creating enough peripheral myopia. Reading glasses and bifocal glasses help a small subset of patients significantly (those with a near esophoria and/or lag of accommodation) , but not a significant help for the majority.
In summary: At the present time, peripheral myopia which has been shown to slow myopic progression, can be created by bifocal contact lenses, special spectacle lenses (currently available only in Hong Kong) and OrthoK lenses.
Outdoor TimeResearch has shown that a child with two myopic parents has a 60% chance of becoming myopic but that spending an average of two hours a day outdoors reduces that risk to 20%. At the present time it is not known what outdoor factor is responsible. It is known that it is not physical activity as there is no additional benefit from being engaged in an active sport.
Possible reasons for the outdoor benefit include smaller pupils from the bright light giving a greater optical depth of field, the ability to focus on objects far away, increased levels of Vitamin D which requires sunlight for the body to produce and increased levels of dopamine in the retina, a growth control signal. There may also be one or more unknown factors.
The effect is not dependent on the amount of near work or reading. In other words, children spending time outdoors do not have to reduce their reading for the effect to be significant.
SummaryAt the present time, the best method of slowing myopia is to spend more time outdoors and investigate methods of creating peripheral myopia with your doctor.
