What is myopia? Who is affected by myopia? What causes myopia?
What is myopia?
Myopia, also known as short-sightedness, is a refractive defect making it difficult to see distant objects clearly. This is because, when the light rays enter the eye, they converge on a plane in front of the retina rather than right on it. This mostly happens because the ocular globe is longer than normal – we say it has a greater axial length.
Using lenses, we move those rays on to the plane of the retina, achieving clear vision.
We can distinguish three main types of myopia:
- Simple or stationary myopia: this usually appears during periods of growth and has a “low” magnitude – less than six dioptres – but no associated damage to the retina.
- Adult-onset myopia: this appears once growth is over and is associated with demanding working conditions.
- Degenerative myopia: this does involve damage to the retina and is usually above six dioptres.
Who is affected by myopia?
Myopia is the most common eye condition in the world, which can begin at a very early age (5-10 years). In the last few years, it has become increasingly prevalent, particularly in South-East Asia. Although not so many people are affected in Europe and the United States, there is evidence of an increase.
According to a study published by the Associación Visión y Vida, in Spain six out of ten people aged between 17 and 27 are short-sighted. The prestigious journal Ophthalmology published an article (Chua WH et al. 2006), from which we can take some interesting figures.
Between 1971 and 1999, prevalence among children in the United States increased from 25% to 42%. In East Asian and South-East Asian countries, with demanding education systems, 80-90% of students finishing secondary education are short-sighted. In these regions, 20% of those affected suffer from pathological myopia (≤-6 D). Myopia is the third cause of blindness in Spain, according to the register of members of ONCE, the charity for the blind.
What causes myopia?
Both genetic and environmental factors have an effect on the development of myopia. Myopia is more prevalent in children with short-sighted parents. Some genes have been associated with myopia and high myopia. However, this effect can be magnified by lifestyle.
Myopia has been associated in various studies with education, close work, urbanisation, prenatal factors, socioeconomic status, cognitive ability, light, and time spent in the open air.
Author: Míriam Garcia