Refractive error, also known as refraction error, is a problem with
focusing light accurately onto the retina due to the shape of the
eye. 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,
astigmatism causes objects to appear stretched out or blurry. Other
symptoms may include double vision, headaches, and eye strain.
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. Some refractive errors occur
more often among those whose parents are affected. Diagnosis is by
Refractive errors are corrected with eyeglasses, contact lenses, or
surgery. Eyeglasses are the easiest and safest method of
Contact lenses can provide a wider field of vision;
however they are associated with a risk of infection. Refractive
surgery permanently changes the shape of the cornea.
The number of people globally with refractive errors has been
estimated at one to two billion. Rates vary between regions of the
world with about 25% of Europeans and 80% of Asians affected.
Near-sightedness is the most common disorder. Rates among adults
are between 15-49% while rates among children are between 1.2-42%.
Far-sightedness more commonly affects young children and the
Presbyopia affects most people over the age of 35.
The number of people with refractive errors that have not been
corrected was estimated at 660 million (10 per 100 people) in 2013.
Of these 9.5 million were blind due to the refractive error. It is
one of the most common causes of vision loss along with cataracts,
macular degeneration, and vitamin A deficiency.
2 Risk factors
8 External links
An eye that has no refractive error when viewing distant objects is
said to have emmetropia or be emmetropic meaning the eye is in a state
in which it can focus parallel rays of light (light from distant
objects) on the retina, without using any accommodation. A distant
object in this case is defined as an object located beyond 6 meters,
or 20 feet, from the eye, since the light from those objects arrives
as essentially parallel rays when considering the limitations of human
An eye that has refractive error when viewing distant objects is said
to have ametropia or be ametropic. This eye cannot focus parallel rays
of light (light from distant objects) on the retina, or needs
accommodation to do so.
The word "ametropia" can be used interchangeably with "refractive
error". Types of ametropia include myopia, hyperopia and astigmatism.
They are frequently categorized as spherical errors and cylindrical
Spherical errors occur when the optical power of the eye is either too
large or too small to focus light on the retina. People with
refractive error frequently have blurry vision.
Nearsightedness: When the optics are too powerful for the length of
the eyeball one has myopia or nearsightedness. This can arise from a
cornea or crystalline lens with too much curvature (refractive myopia)
or an eyeball that is too long (axial myopia).
Myopia can be corrected
with a concave lens which causes the divergence of light rays before
they reach the cornea.
Farsightedness: When the optics are too weak for the length of the
eyeball, one has hyperopia or farsightedness. This can arise from a
cornea or crystalline lens with not enough curvature (refractive
hyperopia) or an eyeball that is too short (axial hyperopia). This can
be corrected with convex lenses which cause light rays to converge
prior to hitting the cornea.
Presbyopia: When the flexibility of the lens declines, typically due
to age. The individual would experience difficulty in near vision,
often relieved by reading glasses, bifocal, or progressive lenses.
Cylindrical errors cause astigmatism, when the optical power of the
eye is too powerful or too weak across one meridian, such as if the
corneal curvature tends towards a cylindrical shape. The angle between
that meridian and the horizontal is known as the axis of the cylinder.
Astigmatism: A person with astigmatic refractive error sees lines of a
particular orientation less clearly than lines at right angles to
them. This defect can be corrected by refracting light more in one
meridian than the other. Cylindrical lenses serve this purpose.
Fundus of person with retinitis pigmentosa, early stage
There is evidence to suggest genetic predilection for refractive
error. Individuals that have parents with certain refractive errors
are more likely to have similar refractive errors.
The Online Mendelian Inheritance in Man (OMIM) database has listed 261
genetic disorders in which myopia is one of the symptoms. Myopia
may be present in heritable connective tissue disorders such as:
Knobloch syndrome (OMIM 267750); Marfan syndrome (OMIM 154700); and
Stickler syndrome (type 1, OMIM 108300; type 2, OMIM 604841).
Myopia has also been reported in X-linked disorders caused by
mutations in loci involved in retinal photoreceptor function (NYX,
RP2, MYP1) such as: autosomal recessive congenital stationary night
blindness (CSNB; OMIM 310500); retinitis pigmentosa 2 (RP2; OMIM
312600); Bornholm eye disease (OMIM 310460). Many genes that have
been associated with refractive error are clustered into common
biological networks involved in connective tissue growth and
extracellular matrix organization. Although a large number of
chromosomal localisations have been associated with myopia
(MYP1-MYP17), few specific genes have been identified.
In studies of the genetic predisposition of refractive error, there is
a correlation between environmental factors and the risk of developing
Myopia has been observed in individuals with visually
intensive occupations. Reading has also been found to be a
predictor of myopia in children. It has been reported that children
with myopia spent significantly more time reading than non-myopic
children who spent more time playing outdoors. Socioeconomic
status and higher levels of education have also been reported to be a
risk factor for myopia.
A doctor uses a trial frame and trial lenses to measure the patient's
Blurry vision may result from any number of conditions not necessarily
related to refractive errors. The diagnosis of a refractive error is
usually confirmed by an eye care professional during an eye
examination using a large number of lenses of different optical
powers, and often a retinoscope (a procedure entitled retinoscopy) to
measure objectively in which the patient views a distant spot while
the clinician changes the lenses held before the patient's eye and
watches the pattern of reflection of a small light shone on the eye.
Following that "objective refraction" the clinician typically shows
the patient lenses of progressively higher or weaker powers in a
process known as subjective refraction.
Cycloplegic agents are
frequently used to more accurately determine the amount of refractive
error, particularly in children
An automated refractor is an instrument that is sometimes used in
place of retinoscopy to objectively estimate a person's refractive
Shack–Hartmann wavefront sensor
Shack–Hartmann wavefront sensor and its inverse can
also be used to characterize eye aberrations in a higher level of
resolution and accuracy.
Vision defects caused by refractive error can be distinguished from
other problems using a pinhole occluder, which will improve vision
only in the case of refractive error.
How refractive errors are treated or managed depends upon the amount
and severity of the condition. Those who possess mild amounts of
refractive error may elect to leave the condition uncorrected,
particularly if the patient is asymptomatic. For those who are
symptomatic, glasses, contact lenses, refractive surgery, or a
combination of the three are typically used.
Strategies being studied to slow worsening include adjusting working
conditions, increasing the time children spend outdoors, and
special types of contact lenses. In children special contact
lenses appear to slow worsening of nearsightedness.
A number of questionnaires exist to determine quality of life impact
of refractive errors and their correction.
DALYs per 100,000 people due to refractive errors in 2004.
less than 100
more than 800
The number of people globally with refractive errors that have not
been corrected was estimated at 660 million (10 per 100 people) in
The number of people globally with significant refractive errors has
been estimated at one to two billion. Rates vary between regions of
the world with about 25% of Europeans and 80% of Asians affected.
Near-sightedness is one of the most prevalent disorders of the eye.
Rates among adults are between 15-49% while rates among children are
Far-sightedness more commonly affects young
children, whose eyes have yet to grow to their full length, and the
elderly, who have lost the ability to compensate with their
Presbyopia affects most people over the
age of 35, and nearly 100% of people by the ages of 55-65.
Uncorrected refractive error is responsible for visual impairment and
disability for many people worldwide. It is one of the most common
causes of vision loss along with cataracts, macular degeneration, and
vitamin A deficiency.
The yearly cost of correcting refractive errors is estimated at 3.9 to
7.2 billion dollars in the United States.
^ a b c d e f g h i j k l m n o p q r "Facts About Refractive Errors".
NEI. October 2010. Archived from the original on 28 July 2016.
Retrieved 29 July 2016.
^ a b c d e Denniston, Alastair; Murray, Philip (2014). Oxford
Ophthalmology (3 ed.). OUP Oxford. p. 826.
ISBN 9780191057021. Archived from the original on
^ a b Foster, PJ; Jiang, Y (February 2014). "Epidemiology of myopia".
Eye (London, England). 28 (2): 202–8. doi:10.1038/eye.2013.280.
PMC 3930282 . PMID 24406412.
^ a b Pan, CW; Ramamurthy, D; Saw, SM (January 2012). "Worldwide
prevalence and risk factors for myopia". Ophthalmic &
physiological optics : the journal of the British College of
Ophthalmic Opticians (Optometrists). 32 (1): 3–16.
doi:10.1111/j.1475-1313.2011.00884.x. PMID 22150586.
^ a b Castagno, VD; Fassa, AG; Carret, ML; Vilela, MA; Meucci, RD (23
December 2014). "Hyperopia: a meta-analysis of prevalence and a review
of associated factors among school-aged children". BMC Ophthalmology.
14: 163. doi:10.1186/1471-2415-14-163. PMC 4391667 .
^ a b Grosvenor, Theodore (2007). Primary care optometry (5 ed.). St.
Louis (Miss.): Butterworth Heinemann, Elsevier. p. 70.
ISBN 9780750675758. Archived from the original on
^ a b c d Global Burden of Disease Study 2013, Collaborators (22
August 2015). "Global, regional, and national incidence, prevalence,
and years lived with disability for 301 acute and chronic diseases and
injuries in 188 countries, 1990-2013: a systematic analysis for the
Global Burden of Disease Study 2013". Lancet. 386 (9995): 743–800.
doi:10.1016/s0140-6736(15)60692-4. PMC 4561509 .
^ a b Pan, CW; Dirani, M; Cheng, CY; Wong, TY; Saw, SM (March 2015).
"The age-specific prevalence of myopia in Asia: a meta-analysis".
Optometry and vision science : official publication of the
American Academy of Optometry. 92 (3): 258–66.
doi:10.1097/opx.0000000000000516. PMID 25611765.
^ Bope, Edward T.; Kellerman, Rick D. (2015). Conn's Current Therapy
2016. Elsevier Health Sciences. p. 354.
^ a b Morgan, Ian; Kyoko Ohno-Matsui (May 2012). "Myopia". The Lancet.
379 (9827): 1739–1748. doi:10.1016/S0140-6736(12)60272-4.
^ a b Wojciechowski, Robert (April 2011). "Nature and Nurture: the
complex genetics of myopia and refractive error". Clin Genet. 79 (4):
^ a b c d Wojcienchowski, Robert (April 2011). "Nature and Nurture:
the complex genetics of myopia and refractive error". National
Institutes of Health. 79 (4): 301–320.
^ Barnes, Katherine (February 2013). "Genome-wide meta-analyses of
multiancestry cohorts identify multiple new susceptibility loci for
refractive error and myopia". Nature Genetics. 45 (3): 314–8.
doi:10.1038/ng.2554. PMC 3740568 . PMID 23396134.
^ Roque, B. Refractive errors in children. Archived 2006-10-19 at the
Wayback Machine. November 2, 2005.
^ "Frequently Asked Questions: How do you measure refractive errors?".
The New York Eye And Ear Infirmary. Archived from the original on
2006-09-01. Retrieved 2006-09-13.
^ "NETRA: Inverse Shack-Hartmann Wavefront Sensor using High
Resolution Mobile Phone Display". Vitor F. Pamplona, Ankit Mohan,
Manuel M. Oliveira, Ramesh Raskar. Archived from the original on
2011-12-21. Retrieved 2011-12-13.
^ a b Li, X; Friedman, IB; Medow, NB; Zhang, C (1 May 2017). "Update
on Orthokeratology in Managing Progressive
Myopia in Children:
Efficacy, Mechanisms, and Concerns". Journal of pediatric
ophthalmology and strabismus. 54 (3): 142–148.
doi:10.3928/01913913-20170106-01. PMID 28092397.
^ Walline, JJ (January 2016). "
Myopia Control: A Review". Eye &
contact lens. 42 (1): 3–8. doi:10.1097/ICL.0000000000000207.
^ Kandel H, Khadka J, Goggin M, Pesudovs K (2017). "Patient-reported
outcomes for assessment of quality of life in refractive error: a
systematic review". Optometry and Vision Science. 94 (12):
^ Kandel H, Khadka J, Lundström M, Goggin M, Pesudovs K (2017).
"Questionnaires for measuring refractive surgery outcomes". Journal of
Refractive Surgery. 33 (6): 416–424.
doi:10.3928/1081597X-20170310-01. PMID 28586503.
^ "WHO Disease and injury country estimates". World Health
Organization. 2009. Archived from the original on 2009-11-11.
Retrieved Nov 11, 2009.
^ Kuryan J, Cheema A, Chuck RS (2017). "Laser-assisted subepithelial
keratectomy (LASEK) versus laser-assisted in-situ keratomileusis
(LASIK) for correcting myopia". Cochrane Database Syst Rev. 2:
CD011080. doi:10.1002/14651858.CD011080.pub2. PMC 5408355 .
PMID 28197998. CS1 maint: Multiple names: authors list
V · T · D
Diseases of the human eye (H00–H59
Thygeson's superficial punctate keratopathy
Pellucid marginal degeneration
Terrien's marginal degeneration
Persistent pupillary membrane
Ocular ischemic syndrome / Central retinal vein occlusion
Central retinal artery occlusion
Bietti's crystalline dystrophy
Central serous retinopathy
Epiretinal membrane (Macular pucker)
Vitelliform macular dystrophy
Leber's congenital amaurosis
Glaucoma / Ocular hypertension / Primary juvenile glaucoma
Leber's hereditary optic neuropathy
Persistent fetal vasculature / Persistent hyperplastic primary
Persistent tunica vasculosa lentis
Familial exudative vitreoretinopathy
Foster Kennedy syndrome
Optic disc drusen
Toxic and nutritional
Chronic progressive external ophthalmoplegia
Esotropia / Exotropia
Conjugate gaze palsy
One and a half syndrome
Anisometropia / Aniseikonia
Leber's congenital amaurosis
Blindness / Vision loss / Visual impairment
Argyll Robertson pupil
Marcus Gunn pupil