What's Happening to Our Vision? Light's Impact on Myopia

7:00 AM

If you are just joining us in our conversation of current working theories for why myopia (near-sightedness) is becoming so much more prevalent in modern society (an increase of 66% since the 1970s!) then check out our previous articles on peripheral defocus theory and near point stress theory.  Remember all of these theories are not meant to stand alone -- our eyes develop over many years into adulthood, and in addition to genetics there are definitely strong environmental factors at play in determining the prescription we end up with.  Today we're discussing some really intriguing research that is surprisingly simple; how can light change how our eyes develop?

The average US classroom is a dim place -- set around 500 lux on average,
but recommended light settings can be around 300 lux for activities like
computer and projector use. image via

More Time Outside is Correlated with Better Vision
For years we looked for an answer to why children became nearsighted in handheld activities. Book reading? Computer games? Cell phones? But study after study showed that these activities didn't strongly correlate with a child's prescription.  In 2007 a study published in Investigative Ophthalmology and Visual Science opened up a new line of thought -- it wasn't the specific activity the child was doing that was associated with myopia, it was the amount of time they spent doing any activity indoors versus outdoors. Researchers followed 514 students from 3rd through 8th grade via surveys that asked parents to report the number of hours a child spent doing different activities and their yearly prescription found at an eye exam.  Any Rx of -0.75D or more counted as myopia. 26% of the students followed became myopic by 8th grade, and the only survey target that strongly correlated with which children ended up nearsighted by the end of the study was the number of hours spent outside or in outdoor sports.  Kids that didn't become myopic during the course of the study spent an average of 11.65 hours outdoors each week, while myopic kids spent an average of only 7.98 hours a week outdoors.  

What's Going On in the Eye?
Why would spending more time outdoors and not specific activities affect how our eyes develop? Outdoor light exposure triggers release of retinal dopamine, a neurotransmitter that helps photoreceptor cells respond to light stimulus.  When dopamine levels within the eye drop, studies in animal models show that the eye enters a cycle of growth or axial lengthening.  The longer the eyeball grows, the more nearsighted the eye becomes.  Chick model studies show strong relationships between eye development and dopamine amounts within the retina.  When newborn chicks were raised with one eye covered for the first 7 days of life, that eye had significantly lower dopamine amounts within the retina than the fellow, open eye.  Interestingly, if the goggle was removed dopamine levels rose to equal amounts as the fellow eye in just 2 days, leading to an idea that it may be possible to treat myopia by increasing dopamine levels within the retina if done early enough in development.  Another study in chick models shows that changing dopamine levels within the retina can begin influending choroidal thickness within just 3 hours, meaning that dopamine levels can have a big effect on how quickly the eye lengthens in young and developing eyes. 

A glass classroom in Yangxi City, China via
The idea has taken off so well that in Asian countries where myopia occurs at a rate of as much as 90% of school age children, outdoor classrooms with glass walls and ceilings are being implemented to extend the number of hours kids are outside without sacrificing learning time in the classroom.  In Taiwan, a small study yielded promising results -- kids that spent 80 minutes outdoors had a rate of myopia development of only 8% while a cohort group under normal classroom environment conditions had an 18% rate of myopia development that year. 

How much sunlight does your child need?  
This is a question that we are far from answering, but studies are suggesting a good starting place. Dr. Ian Morgan is the lead researcher behind China's outdoor classroom project, and recommends 3 hours per day of light at least 10,000 lux for children to help prevent myopia.  10,000 lux isn't full, mid-day sun -- it's equivalent to a shady spot under a tree or an overcast day.  But by comparison, an average classroom or office workspace only has around 500 lux.  That's a huge difference in ambient light level, even though we often imagine that a lit room indoors would be brighter than reading a book outside in the shade. As larger and more investigative studies are performed, we may even see changes in classroom lighting requirements to better mimic the luminance of natural, outdoor light. Some research is even being done to investigate the use of 10,000 lux lamps commonly used to help treat Seasonal Affective Disorder, but there are always worries about the danger of UV exposure and its risk for retinal damage.  We don't yet know how much light is safe without permanently damaging the eye, so at this time it is best to recommend spending more time outdoors, but also being proactive about UV protection with sunscreen and sunglasses.  A study of over 1,000 young adults aged 19 to 22 in Australia confirmed that eyes that were more myopic had statistically significant less sun damage found via UV photography of the conjunctiva than the persons whose eyes had better vision.  Right now researchers are having to balance the pros and risks of increasing exposure to UV light, so more studies are definitely needed before we see a blanket recommendation for hours in the sun.

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