-The EYE Digest-
Myopic Insight - How Did We Become Nearsighted?
Glasses. Contact Lenses. LASIK. All of these terms are commonplace in modern society. You may be familiar with one or more of these modalities from your own vision care or a family member or friend. The truth is, nearsightedness (myopia) has become so prevalent that there are no degrees of separation when we seek to find individuals suffering from the condition.
In fact, a recent study has shown that myopia affects nearly 1.6 billion people across the world. The incidence of myopia is nearly 42% in the US, and in countries such as Singapore and Hong Kong, it is a staggering 80%!
So the question arises: how did we become nearsighted? Additionally, why are the rates of myopia increasing at such a drastic rate in the modern age? Sure, myopia will always have a genetic component, but certainly an environmental component must also be coming into play. In fact, it is more than likely a mixture of the two components is responsible for most cases of myopia. Let’s take a look at the theories that have been postulated to explain this phenomenon.
Genetic Theory – Mutation in LEPREL1
It is generally accepted that if a parent or both parents of a child are myopic, this places the child at a higher likelihood of developing myopia. In fact, a genome-wide linkage analysis has found that a mutation on exon 10 of the gene named LEPREL1 has a direct correlation with myopia.
Environmental Theory #1 - Reading Time vs. Outdoor Activities
The most common theory used to explain the up tick in myopia is the amount of time children
spend indoors performing up close tasks (such as reading) vs. the amount of time they spend outdoors playing. Prolonged amounts of time performing activities such as reading books, looking at laptops, playing on tablets, and working on smart phone screens have been linked to myopia in children.
The idea behind these activities causing myopia deals with the higher amount of accommodation and strain involved with prolonged near work, which can have a link to increased axial length, which subsequently can turn an emmetropic (no prescription) eye into a myopic eye.
We can see the correlation between myopia and near activity through a historical standpoint. One hundred years ago, many children spent most of their time outside tending to farms and handiwork while doing minimal indoor close up work. The incidence of myopia around this time was much lower than it is today.
Further evidence comes from the Avon Longitudinal Study of Parents and Children (ALSPAC), which found that longer amounts of time spent outdoors resulted in a lower incidence of myopia in children 3 years of age and up.
The correlation between outdoor activity and less myopia has also led researchers to believe that amount of exercise during childhood may also lead to a lower incidence of myopia.
Environmental Theory #2 – Direct Light Exposure
While the reading/near activity link seems to be the most accepted theory for environmental causation of myopia, recent research has shed some light on the effects of sunlight on myopia development. Specifically, it may be the outdoor activities that are helping to prevent myopia, rather than the indoor activities that are causing myopia.
Correlation between increased exposure to light and a lower incidence of myopia has been found. Two hypotheses exist for this correlation. The first hypothesis is that sunlight causes the release of vitamin D, which may have an affect in halting eye growth and thus myopia. The second is that sunlight causes a dopamine release in the retina, which results in a cascade of cellular reactions that lead to normal eye growth.
In conclusion, the moral of the story is that a genetic component as well as an environmental component comes into play with development of myopia. With the knowledge we have, a two-fold plan can be made to potentially reduce the risk of myopic progression in children:
- 1) Make sure your children spend an ample amount of time playing outside, especially if you or your spouse is myopic!
- 2) Make sure your children take frequent breaks when performing near tasks. We often recommend the 20-20-20 rule: every 20 minutes, take 20 seconds to look 20 feet away.
-Dr. Aaron Neufeld
Dr. Aaron Neufeld is the Chief Optometrist at Los Altos Optometric Group and primary author and editor of The EYE Digest.
Contact him with questions or ideas for future articles at (650) 948-3700 or firstname.lastname@example.org