Refractive error | |
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Other names | Refraction error |
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A correctly-focused eye (top), and two showing refractive error: in the middle image, the light is focused too far forward; in the bottom image, the focal point is behind the eye | |
Specialty | Ophthalmology, optometry |
Symptoms | Blurry vision, double vision, headaches, eye strain |
Complications | Blindness, amblyopia[1][2] |
Types | Near-sightedness, far-sightedness, astigmatism, presbyopia[3] |
Causes | Eyeball length, problems with cornea shape, aging of the lens[3] |
Diagnostic method | Eye examination[3] |
Treatment | Eyeglasses, contact lenses, refractive surgery[3] |
Frequency | ~1.5 billion[4] |
Refractive error is a problem with focusing light accurately on the retina due to the shape of the eye and/or cornea.[3] The most common types of refractive error are near-sightedness, far-sightedness, astigmatism, and presbyopia. Near-sightedness results in far away objects being blurry, far-sightedness and presbyopia result in close objects being blurry, and astigmatism causes objects to appear stretched out or blurry. Other symptoms may include double vision, headaches, and eye strain.[3]
Near-sightedness is due to the length of the eyeball being too long, far-sightedness the eyeball too short, astigmatism, the cornea being the wrong shape, and presbyopia aging of the lens of the eye such that it cannot change shape sufficiently.[3] Some refractive errors occur more often among those whose parents are affected.[3] Diagnosis is by eye examination.[3]
Refractive errors are corrected with eyeglasses, contact lenses, or surgery.[3] Eyeglasses are the easiest and safest method of correction.[3] Contact lenses can provide a wider field of vision; however they are associated with a risk of infection.[3] Refractive surgery permanently changes the shape of the cornea.[3]
The number of people globally with refractive errors has been estimated at one to two billion.[4] Rates vary between regions of the world with about 25% of Europeans and 80% of Asians affected.[4] Near-sightedness is the most common disorder.[5] Rates among adults are between 15 and 49% while rates among children are between 1.2 and 42%.[6] Far-sightedness more commonly affects young children and the elderly.[7][8] Presbyopia affects most people over the age of 35.[3]
The number of people with refractive errors that have not been corrected was estimated at 660 million (10 per 100 people) in 2013.[9] Of these 9.5 million were blind due to the refractive error.[9] It is one of the most common causes of vision loss along with cataracts, macular degeneration, and vitamin A deficiency.[10]
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