Short sidedness appears to have reached epidemic proportions worldwide. This has been particularly evident in East Asia where today up to 90% of Chinese teenagers and adults are myopic and a remarkable 96.5% of 19 year-old males in Seoul Korea are myopic. New scientific studies are now shedding light on the emerging pandemic.
In general myopia is attributed to the slight elongation of the eye that results in the visual image falling in front of the retina. In its most severe form this elongation can become pathological predisposing individuals to risk of retinal hole formation, detachment and macular degeneration. Older theories have attributed myopia to be influenced by excessive near work by bookish children and in fact the modern rise in myopia has tended to mirror a trend with children in many countries who now spend excessive amounts of time on their computers and smart phone. These behaviors seem to be prevalent in Asian cultures where educational performance is stressed. It seemed logical that sustained close work could influence the growth and elongation of the eye as it tries to focus close up images. Inheritance factors have also been cited in studies of identical and non identical twins for myopia. However, recent studies have produced a new compelling theory on the rapid rise of worldwide myopia.
In the early 2000’s researchers examining such behaviors were unable to find an association of prolonged near work with myopia but in 2007 scientists at Ohio State University who followed 500 eight and nine year old California children with healthy vision examining how they spent their days. After five years of study they found one in five developed myopia and the only compelling risk factor in those afflicted is that they spent significantly less time out of doors. A similar study of 4000 Australian kids came to the very same conclusion and the observation that the greater exposure to environmental light might be protective against the development of myopia. (1)
Animal studies have also supported this theory as it has been documented that myopia can be induced in chicks through ocular occlusion and further it has been documented that under controlled conditions when exposed to higher levels of light illumination, comparable to outside conditions, had a much lower level of myopia when compared to those that were limited to indoor levels of light intensity (2). Studies on primates have come to the same conclusions. And in a 2009 study of over 900 Chinese six and seven year olds over a three-year period it has been determined that those who attended out door classes 30% developed myopia as compared to 40% of those studied under control schools. A similar Taiwanese study showed that when teachers seen their children outside for 80 minutes per day they developed myopia 8% of the time as compared to 18% at a nearby school over an identical period of time.(3)
Current thinking explains that the development of myopia is linked to retinal dopamine that is released in greater amount during bright light exposure. This chemical is known to be produced in a diurnal cycle which ramps up during the day when vision switches from a rod biased dim light situation to a bright light cone based vision. Researchers now believe that under dim light indoor lighting that the cycle of dopamine release is disrupted with a consequential influence on eye growth.
It is now believed that children need to spend around three hours per day under light levels of 10,000 lux in order to be protected against myopia or the equivalent illumination exposure on a bright day wearing sunglasses under a shady tree. The typical light intensity in a well-lit classroom or office pales in comparison at no more than 500 lux. The norm in the United States, Europe and East Asia is one to two hours at most.
- Rose, K. A. et al. Ophthalmology115, 1279–1285 (2008).
- Ashby, R., Ohlendorf, A. & Schaeffel, F. Ophthalmol. Vis. Sci.50, 5348–5354 (2009).Rose, K. A. et al. Ophthalmology 115, 1279–1285 (2008).
- Wu, P.-C., Tsai, C.-L., Wu, H.-L., Yang, Y.-H. & Kuo, H.-K. Ophthalmology120, 1080–1085(2013).