The myopia is a condition increasingly widespread globally, but several studies conducted in recent decades have shown that some geographical areas are more affected than others. Children living in countries such as China, Singapore and Taiwan, for example, tend to suffer from more severe forms of myopia and manifest them earlier than children of the same age growing up in other parts of the world. Researchers studying myopia have advanced two theories that could explain these differences between populations:
- a first theory holds that the differences are related to a different genetic predisposition. Myopia, in fact, is a disorder due to a slight deformation of the eyewhich stretches excessively along its axis, causing blurred vision of objects. According to proponents of the genetic theory, some ethnic groupssuch as theHispanic and theAsian, would have a major predisposition to incur this type of malformation;
- other researchers, on the other hand, argue that the difference between the various populations is too marked to be due solely to genetic causes and suggest the involvement of certain environmental factors.
Understanding why some populations are more affected than others is a matter of great importance, as it could help to identify the dynamics that lead to the onset of myopia and to promote therapeutic strategies to address the causesrather than correcting the symptoms.
Nearsightedness and exposure to light
Studies conducted in recent years have produced a considerable amount of data confirming the influence of certain environmental factors on the onset of myopiafirst of all time spent outdoors. It seems, in fact, that spending daily time in the open air decrease the risk of myopia occurrenceprobably because of theexposure to intense sunlightwhich stimulates the release of dopamine in the retina.
Dopamine is a neurotransmitter that plays an important role as a chemical mediator in the growth of retinal tissue and the proper development of visual and refractive function. Dopamine contributes, among other things, to making the sclera, the cartilaginous membrane of the eye that tends to expand in the myopic eye, less elastic. Exposure to fresh air and sunlight stimulates dopamine production, while closed environments inhibit it, inducing more elasticity in the sclera and thus favouring myopia. Confirming this, some drugs such as atropine, which mimic the effects of dopamine, are able to counteract the elongation of the eyeball responsible for myopia.
The importance of sunlight would be confirmed by numerous searchesOne of which compared six- and seven-year-old Chinese children, some of whom live in Singapore while others reside in Australia. Among children who live in Australia, and who routinely spend about 14 hours a week outdoors, only 3.3% were found to have myopia, compared to 29.1% of children who live in Singapore, and who on average spend only 3 hours a week outdoors. The prevalence of myopia in many eastern countriesin which this disorder has epidemic proportionscould, therefore, be linked to their rigid school system which requires children to spend many hours in classrooms, and to spend a lot of time doing homework. Added to this situation is the habit of today's children to spend the free time in front of a screenbe it the TV or any electronic device, rather than playing in the open air.
In accordance with the results of this research, the governments of some of the most affected countries have put in place some awareness-raising campaigns to encourage children to spend more time outdoors. This strategy, however, raises two problems:
- the need for changing a cultural model which places the importance of academic performance above health;
- the risk which, when exposed to sunlight for many hours, is increase the risk of skin cancer. Some research, however, has shown that the protective effect exerted by sunlight is also associated with theexposure to intense artificial light, free of harmful UV rays. The use of special lamps for indoor use could, therefore, be a solution.
Research has already made important steps forward in understanding the correlation between myopia and the environment, but it is necessary to continue along this path in order to clarify the many doubts and to enable increasingly effective intervention strategies and therapies to be developed in the future.
Sources
- Lougheed T. Myopia and environmental factors. Social Ophthalmology. 2014; 3:36-43
- Feldkaemper M1, Schaeffel F. An updated view on the role of dopamine in myopia. Exp Eye Res. 2013 Sep;114:106-19.
- Xiong S, Sankaridurg P, Naduvilath T, et al. Time spent in outdoor activities in relation to myopia prevention and control: a meta-analysis and systematic review. Acta Ophthalmol. 2017 Sep;95(6):551-566.
Dr. Carmelo Chines
Direttore responsabile
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