Prevalence of myopia
The prevalence corresponds to the percentage of short-sighted in a population at a given time. Myopia usually appears in childhood, and to consider that studies often address different age populations. The prevalence of nearsightedness rising everywhere in the world, but this acceleration seems stronger in Asia.
Prevalence of myopia in adults
The prevalence of myopia seems more pronounced for Asian countries.
Here are some figures for the prevalence of myopia in adults in some Asian countries:
Taiwan (Age > 65 years) Prevalence: 19.4% - Cheng (2003)
Japan (Age > 40 years) Prevalence: 41.8%-Sawada (2007)
China (Age > 40 years) Prevalence: 22.9% - Xu (2005)
India (Age > 40 years) Prevalence: 34.6% - Krishnaiah (2009)
Singapore (Age > 40 years) Prevalence: 38.7%-Wong (2000)
Overall, the prevalence of myopia seems a little less strong in Western countries:
USA (Age > 40 years) Prevalence: 16.8% - Tarczy-Hornoch (2006)
Australia (Age > 40 years) Prevalence: 17% - Wensor (1999)
Norway (Age > 40 years) Prevalence: 30.3% Midelfart (2002)
In France, there is not well framed recent study to assess the prevalence of nearsightedness; the Union of the French ophthalmologists (snof) reported 39% without specifying a range of age or mtehodologie to study (sample, age, etc.).
However, the prevalence for the studies reported above figures are indicative. They are studies on limited samples (although made up of thousands of individuals). There are some limits or differences as the threshold of myopia chosen (most often defined as greater than 0.5 D), the method of measure for refraction, etc. In addition, there are sometimes variability related to ethnicity within the same sample. For example, adult Singaporeans of Chinese origin are more myopic than those of Indian or Malay origin.
Prevalence of myopia in children
The difference in prevalence of myopia among Asian children to Western children is more pronounced than in adults. However, this difference is modulated according to certain environmental factors: it is growing in urban areas and improves rural.
Children Chinese high in urban areas, the prevalence of myopia increases of 5.7% (5 years)) 30.1% (10 years) then 78.4% (15 years old))He et al. Refractive error and visual impairment in urban children in southern china. Invest invest live Sci 2004; 45:793 - 799). Carried out in rural areas in the North of China, a similar methodology study found a prevalence of myopia almost zero at the age of 5 years, and 55.0% at the age of 15 years)Zhao et al. Refractive error study in children: results from Shunyi District, China. Am J invest 2000; 129: 427-435). However, these figures are higher than those measures in other regions of the world.
In South Africa, the prevalence of myopia has been measured at 9.6% at the age of 15 years)Naidoo et al. Refractive error and visual impairment in African children in South Africa. Invest invest live Sci 2003; 44: 3764-3770). In Chile, a study found a prevalence of myopia of 19.4% for boys of 15, against 14.7 percent for girls of the same age)Maul et al. Refractive error study in children: results from La Florida, Chile. Am J invest 2000; 129: 445-454). In Northern Ireland, a study led in a Caucasian children found a prevalence of myopia equal to 2.8% in the age group 6-7 years, and of 17.7% in the 12-13 age group)O'Donoghue et al. Refractive error and visual impairment in school children in Northern Ireland. BR JOphthalmol 2010; 94: 1155-1159). Thus, for identical environmental conditions, the prevalence of myopia is stronger for African or Asian than European children children.
The prevalence of myopia in children raised in urban areas is higher than that of children raised in rural areas. These epidemiological data suggest the influence of genetic and environmental elements as risk factors for myopia.