By Anne Laing.
It seems more recently that we’re always glued to some screen or another.
Yet the addiction to screen use goes beyond its attention-grabbing nature, and need to be constantly updated and aware.
Screen-time creates a very near and static focal length for our eyes…The ciliary muscle in the eye relaxes when looking into the distance, and it contracts at shorter focal lengths.
Gazing at a screen for hours on end is effectively practicing constant contraction of the ciliary muscle. Too much ‘near’ work, in the absence of ‘mid-range’ and ‘distance’ work, influences the progression of myopia (short-sightedness)
Being office and home-bound reduces time spent outside, which is also suggested to lead to myopia.
Based on epidemiological studies, Ian Morgan, a myopia researcher at the Australian National University in Canberra, estimates that children needed to spend around three hours per day under light levels of at least 10,000 lux to be protected against myopia.
When outdoors, the eye becomes accustomed to long viewing distances, and this has a protective effect. This ability was essential for primeval man to perceive hidden danger, changes in terrain and weather patterns in order to survive.
When the eye is exposed to bright light, the retina releases dopamine. Dopamine signals the eye to change from night vision, which relies on rod-shaped photoreceptors, to day vision mode. Day vision utilises cone-shaped photoreceptors, which also provide colour sensitivity. When there isn’t enough of the right light, this cycle gets disrupted.
Overcast days may provide less than 10,000 lux – even outdoors – but sunny days can provide much more than that, even if you’re wearing sunglasses. Indoor settings typically max out at about 500 lux, so make sure you get out of the office and off the sofa – and into the bright light of day as often as you can.
Nature 519,276–278 (19 March 2015) International weekly journal of science http://www.nature.com/news/the-myopia-boom-1.17120