What is nearsightedness?
myopia | 近視
'Inability to see clearly in the distance; can see better at near than far away; a condition of the eye that causes distant objects to appear blurred because their images are focused in front of the retina rather than on it.'
Also called short-sightedness, near-sightedness.
What causes myopia?
Genetics and environmental factors both contribute to the development of myopia in children and adolescents.
A family history of myopia is a known risk — one or both parents with short-sightedness significantly increases the risk of the child developing it also.
Environmental influences include excessive near work, reading, studying, computer and tablet use, and time spent indoors. Significant growth of the eye occurs in children between the ages of 6 and 12. During this critical time, factors which increase the risk of abnormal elongation growth of the eye will result in myopia.
As society has developed with urbanization, education and constant use of digital technology in everyday life from a young age, the evolution of the human eye has not kept up with these rapid changes. That's why myopia in children and young adults is dramatically on the rise. Myopia is becoming such a problem all around the world that it's been termed The Myopia Epidemic by eye experts and researchers.
Degree of myopia
Myopia is generally classified according to the degree of myopia, that is the power of the prescription lens required to correct the blurred vision, measured in dioptres (D). The higher the myopia, the greater the physical elongation of the eye.
Low myopia -0.50 to -3.00
Moderate myopia -3.00 to -5.00
High myopia -5.00 and above
Extreme myopia is sometimes used to describe myopia in excess of -10.00
In some countries, the amount of myopia may be specified in 'degrees'. For example, -6.00 is commonly referred to in Hong Kong and south-east Asia as 600 degrees of myopia (600 度近視), and -10.00 as 1000 degrees of myopia (1000 度近視), and so on.
Consequences of High Myopia
Glasses become thicker and heavier with higher levels of myopia. High-index lenses to reduce thickness add extra expense to each pair of new glasses.
High myopia is associated with cataract formation, and also increases the risk of complications during and after cataract surgery.
High myopia has been linked to a higher incidence of glaucoma, and development of more severe cases of glaucoma.
Myopia commonly causes earlier vitreous detachment, leading to many visually-disruptive spots and floaters and increases glare.
Thinning of the retina in a highly myopic eye increases the risk of developing myopic macular degeneration, causing loss of central vision.
Retinal detachment is one possible consequence of high myopia. Retinal detachment surgery to repair a torn retina and restore sight is a complex, risky and invasive procedure. Vision may never fully return to normal.