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Refraction error
""Reading-Glasses.jpg
Glasses are a common treatment for refractive errors
"Specialty "Ophthalmology
Symptoms "Blurry vision, "double vision, "headaches, "eye strain[1]
Types "Near-sightedness, "far-sightedness, "astigmatism, "presbyopia[1]
"Diagnostic method "Eye examination[1]
Treatment "Eyeglasses, "contact lenses, "surgery[1]
Frequency ~1.5 billion[2]

Refractive error, also known as refraction error, is a problem with "focusing "light accurately onto the "retina due to the shape of the "eye.[1] The most common types of refractive error are "near-sightedness, "far-sightedness, "astigmatism, and "presbyopia.[1] 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.[1] Other symptoms may include "double vision, "headaches, and "eye strain.[1]

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.[1] Some refractive errors occur more often among those whose parents are affected.[1] Diagnosis is by "eye examination.[1]

Refractive errors are corrected with "eyeglasses, "contact lenses, or "surgery.[1] Eyeglasses are the easiest and safest method of correction.[1] Contact lenses can provide a wider "field of vision; however they are associated with a risk of infection.[1] "Refractive surgery permanently changes the shape of the cornea.[1]

The number of people globally with refractive errors has been estimated at one to two billion.[2] Rates vary between regions of the world with about 25% of Europeans and 80% of Asians affected.[2] Near-sightedness is the most common disorder.[3] Rates among adults are between 15-49% while rates among children are between 1.2-42%.[4] Far-sightedness more commonly affects young children and the elderly.[5][6] Presbyopia affects most people over the age of 35.[1] The number of people with refractive errors that have not been corrected was estimated at 660 million (10 per 100 people) in 2013.[7] Of these 9.5 million were "blind due to the refractive error.[7] It is one of the most common causes of "vision loss along with "cataracts, "macular degeneration, and "vitamin A deficiency.[8]

Contents

Classification[edit]

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 perception.[9]

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 errors:

Risk factors[edit]

Genetics[edit]

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""
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.[1]

The Online Mendelian Inheritance in Man (OMIM) database has listed 261 genetic disorders in which myopia is one of the symptoms.[10] 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).[11] 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).[12] Many genes that have been associated with refractive error are clustered into common biological networks involved in connective tissue growth and extracellular matrix organization.[11] Although a large number of chromosomal localisations have been associated with myopia (MYP1-MYP17), few specific genes have been identified.[10]

Environmental[edit]

In studies of the genetic predisposition of refractive error, there is a correlation between environmental factors and the risk of developing myopia.[13] Myopia has been observed in individuals with visually intensive occupations.[12] 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.[12] Socioeconomic status and higher levels of education have also been reported to be a risk factor for myopia.

Diagnosis[edit]

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""
A doctor uses a trial frame and trial lenses to measure the patient's refractive error.

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[14]

An "automated refractor is an instrument that is sometimes used in place of "retinoscopy to objectively estimate a person's refractive error.[15] "Shack–Hartmann wavefront sensor and its inverse[16] 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.

Management[edit]

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,[12] and special types of contact lenses.[17] In children special contact lenses appear to slow worsening of nearsightedness.[17][18]

Epidemiology[edit]

""
""
"DALYs per 100,000 people due to refractive errors in 2004.[19]
  no data
  less than 100
  100-170
  170-240
  240-310
  310-380
  380-450
  450-520
  520-590
  590-660
  660-730
  730-800
  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 2013.[7]

The number of people globally with significant refractive errors has been estimated at one to two billion.[2] Rates vary between regions of the world with about 25% of Europeans and 80% of Asians affected.[2] Near-sightedness is one of the most prevalent disorders of the eye.[3] Rates among adults are between 15-49% while rates among children are between 1.2-42%.[4] 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 "accommodation system.[5][6] Presbyopia affects most people over the age of 35, and nearly 100% of people by the ages of 55-65.[1] Uncorrected refractive error is responsible for visual impairment and disability for many people worldwide.[7] It is one of the most common causes of "vision loss along with "cataracts, "macular degeneration, and "vitamin A deficiency.[8]

Cost[edit]

The yearly cost of correcting refractive errors is estimated at 3.9 to 7.2 billion dollars in the United States.[20]

References[edit]

  1. ^ 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. 
  2. ^ a b c d e Denniston, Alastair; Murray, Philip (2014). Oxford Handbook of Ophthalmology (3 ed.). OUP Oxford. p. 826. "ISBN "9780191057021. Archived from the original on 2016-08-15. 
  3. ^ 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 3930282Freely accessible. "PMID 24406412. 
  4. ^ 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. 
  5. ^ 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 4391667Freely accessible. "PMID 25539893. 
  6. ^ 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 2016-08-15. 
  7. ^ 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 4561509Freely accessible. "PMID 26063472. 
  8. ^ 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. 
  9. ^ Bope, Edward T.; Kellerman, Rick D. (2015). Conn's Current Therapy 2016. Elsevier Health Sciences. p. 354. "ISBN "9780323355353. 
  10. ^ a b Morgan, Ian; Kyoko Ohno-Matsui (May 2012). "Myopia". The Lancet. 379 (9827): 1739–1748. "doi:10.1016/S0140-6736(12)60272-4. 
  11. ^ a b Wojciechowski, Robert (April 2011). "Nature and Nurture: the complex genetics of myopia and refractive error". Clin Genet. 79 (4): 301–320. "doi:10.1111/j.1399-0004.2010.01592.x. 
  12. ^ 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. "doi:10.1111/j.1399-0004.2010.01592.x. 
  13. ^ 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 3740568Freely accessible. "PMID 23396134. 
  14. ^ Roque, B. Refractive errors in children. Archived 2006-10-19 at the "Wayback Machine. November 2, 2005.
  15. ^ "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. 
  16. ^ "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. 
  17. ^ 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. 
  18. ^ Walline, JJ (January 2016). "Myopia Control: A Review". Eye & contact lens. 42 (1): 3–8. "doi:10.1097/ICL.0000000000000207. "PMID 26513719. 
  19. ^ "WHO Disease and injury country estimates". World Health Organization. 2009. Archived from the original on 2009-11-11. Retrieved Nov 11, 2009. 
  20. ^ 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. "PMID 28197998. 

External links[edit]

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