Myopia is a refractive defect of the eye in which collimated light produces image focus in front of the retina when accommodation is relaxed.
Those with myopia see near objects clearly but far away objects appear blurred.
With myopia, the eyeball is too long, or the cornea is too steep, so images are focused in the vitreous inside the eye rather than on the retina at the back of the eye.
The opposite defect of myopia is hyperopia or "farsightedness" or "long-sightedness"—this is where the cornea is too flat or the eye is too small.
Eye care professionals most commonly correct myopia through the use of corrective lenses, such as glasses or contact lenses.
It may also be corrected by refractive surgery, but this does have many risks and side effects. The corrective lenses have a negative optical power (''i.e.'' are concave) which compensates for the excessive positive diopters of the myopic eye.
Alternative ideas and methods of treatment exist, most notably the claim that myopia is caused by excessive near sight work.
The global prevalence of refractive errors has been
estimated from 800 million to 2.3 billion.
The incidence of myopia within sampled population often
varies with age, country, sex, race, ethnicity, occupation, environment,
and other factors. Variability in testing and data collection methods
makes comparisons of prevalence and progression difficult.
In some areas, such as China, India and Malaysia, up to 41%
of the adult population is myopic to -1dpt, up to 80% to -0.5dpt.
A recent study involving first-year undergraduate students
in the United Kingdom found that 50% of British whites and 53.4% of
British Asians were myopic.
In Australia, the overall prevalence of myopia (worse than
−0.50 diopters) has been estimated to be 17%. In one recent study, less
than 1 in 10 (8.4%) Australian children between the ages of 4 and 12
were found to have myopia greater than −0.50 diopters.
A recent review found that 16.4% of Australians aged 40 or
over have at least −1.00 diopters of myopia and 2.5% have at least −5.00
In Brazil, a 2005 study estimated that 6.4% of Brazilians
between the ages of 12 and 59 had −1.00 diopter of myopia or more,
compared with 2.7% of the indigenous people in northwestern Brazil.
Another found nearly 1 in 8 (13.3%) of the students in the
city of Natal were myopic.
In Greece, the prevalence of myopia among 15 to 18 year old
students was found to be 36.8%.
In India, the prevalence of myopia in the general population
has been reported to be only 6.9%.
A recent review found that 26.6% of Western Europeans aged
40 or over have at least −1.00 diopters of myopia and 4.6% have at least
Approximately 25% of Americans between the ages of 12 and 54
have the condition. A recent review found that 25.4% of Americans aged
40 or over have at least −1.00 diopters of myopia and 4.5% have at least
Ethnicity and race
The prevalence of myopia has been reported as high as 70–90%
in some Asian countries, 30–40% in Europe and the United States, and
10–20% in Africa.
Education and myopia
A number of studies have shown that the incidence of myopia
increases with level of education have shown a correlation between
myopia and IQ, likely due to the confounding factor of formal education.
Other personal characteristics, such as value systems,
school achievements, time spent in reading for pleasure, language
abilities and time spent in sport activities correlated to the
occurrence of myopia in studies.
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