Myopia is now regarded by WHO as a global epidemic. On average, developed and developing nations have experienced a three-fold increase in myopia over the past three decades. In South Korea, China and most of eastern Asia, 80 percent of high school graduates and 95 percent of university graduates are myopic. Apart from the personal costs, inconvenience and disability, myopia brings elevated risk of ocular morbidity for many of these sufferers in later life (glaucoma, macular degeneration, retinal detachment and cataract) which in turn poses the risk of an onerous burden on health and welfare costs both at a personal and State level.
Once thought to be due to prolonged reading and close work, researchers in the vision sciences showed that a leading cause of myopia is reduced exposure to specific wavelengths in sunlight and their beneficial effect beginning at the retinal level. Laboratory research and studies on trends in myopia within human populations now suggests that the ‘retinal dopamine response’ instigated by the non-visual light receptors of the retina, the so-called ‘intrinsically photosensitive retinal ganglion cells’ or ipRGC’s, which control eye-growth and therefore the pathogenesis of myopia. The remedy for myopia was to be found in a strategically beneficial wavelength of sunlight, quite specifically at 480nm a version of blue light we learnt in school as ‘indigo’. Without a threshold amount of stimulation to the ipRGC’s eye growth has the tendency to continue unabated. The axial length of the eye becomes abnormally long to match the optics of the front of the eye (cornea and lens) and the image of distant objects is focussed before reaching the retina. Objects then only come into focus if they are close to the eye, creating the effect of being ‘near sighted’ or myopic.
One other function of ipRGC’s is their control over the sustained pupillery light reflex. When light is directed towards the eye the pupil typically closes down. This immediate response happens from light falling upon the rods and cones. However, within a few micro-seconds, the ipRGC’s take over the pupil response and then control the size of the pupillery aperture. This is important in limiting the retinal exposure to bright light as well as helping maintain a sharper retinal image and improving the range of the depth of field rendered by the optics of the eye.
Introduction
2 hours of sunlight
on average per day
dramatically
slows myopic
progression