{{Short description|Type of optical machine}} [[File:US Navy 080812-N-9774H-106 Hospitalman Michael Hagglund, an optometrist technician embarked aboard the amphibious assault ship USS Kearsarge (LHD 3), uses an auto refractor to help determine eye prescriptions on a patient at Ju.jpg|thumb|A United States Navy optometrist technician using an autorefractor during a humanitarian assistance project in Nicaragua in 2008]] An '''autorefractor''' or '''automated refractor''' is a computer-controlled machine used during an eye examination to provide an objective measurement of a person's refractive error and prescription for glasses or contact lenses. This is achieved by measuring how light is changed as it enters a person's eye.
==Technique== thumb|Shin Nippon Nvision K-5001 Refkeratometer thumb|The optics inside a Shin Nippon Nvision K-5001 Refkeratometer The majority of autorefractors calculate the vision correction a patient needs (refraction) by using sensors that detect the reflections from a cone of infrared light. These reflections are used to determine the size and shape of a ring in the retina which is located in the posterior part of the eye. By measuring this zone, the autorefractor can determine when a patient's eye properly focuses an image. The instrument changes its magnification until the image comes into focus. The process is repeated in at least three meridians of the eye and the autorefractor calculates the refraction of the eye, sphere, cylinder and axis. Modern autorefractors are based on the idea patented by Antonio Medina Puerta.<ref name="Medina ">{{Cite web |url=http://www.espatentes.com/pdf/8100872_A1.pdf |title=Medina A.: "Refractometro Electronico (Electronic Refractor)". Spanish patent. Jul 1979. |access-date=2015-11-09 |archive-url=https://web.archive.org/web/20160825234222/http://www.espatentes.com/pdf/8100872_A1.pdf |archive-date=2016-08-25 |url-status=dead }}</ref>
==Uses== In some offices, this process is used to provide the starting point for the ophthalmologist or optometrist in subjective refraction tests. Here, lenses are switched in and out of a phoropter and the patient is asked "which looks better" while looking at a chart. This feedback refines the prescription to one which provides the patient with the best vision.
Automated refraction is particularly useful when dealing with non-communicative people such as young children or those with disabilities.
==Retinoscopy== Retinoscopy performed by an experienced clinician has been found to provide a more accurate estimation of refractive error than autorefraction.<ref>{{cite journal | author = Jorge J, Queiros A, Almeida JB, Parafita MA | date = Jan 2005 | title = Retinoscopy/autorefraction: which is the best starting point for a noncycloplegic refraction? | url = | journal = Optom Vis Sci| volume = 82 | issue = 1| pages = 64–8 | pmid = 15630406 }}</ref> Recent studies report that autorefractor measurements without application of cycloplegia medication can result in significant overestimation of myopia.<ref>{{cite journal | author = Choong YF, Chen AH, Goh PP | date = Jul 2006 | title = A comparison of autorefraction and subjective refraction with and without cycloplegia in primary school children | url = | journal = Am J Ophthalmol | volume = 142 | issue = 1| pages = 68–74 | pmid = 16815252 | doi = 10.1016/j.ajo.2006.01.084 }}</ref><ref>{{cite journal | author = Fotedar R, Rochtchina E, Morgan I, Wang JJ, Mitchell P, Rose KA | date = Aug 2007 | title = Necessity of cycloplegia for assessing refractive error in 12-year-old children: a population-based study | url = | journal = Am J Ophthalmol | volume = 144 | issue = 2| pages = 307–9 | pmid = 17659966 | doi = 10.1016/j.ajo.2007.03.041 }}</ref>
==References== {{reflist}}
==External links== {{Commons category|Autorefractors}} * Trusit Dave "Automated refraction - Design and applications" in "Optometry Today" 04/06/04 [https://web.archive.org/web/20141222180646/http://www.optometry.co.uk/uploads/articles/ae331f5e9f3c12ab8e23e345f22b45d4_dave20040604.pdf] * "This Company Is Bringing Eye Exams (And Glasses) To People Who Can't Afford Healthcare". Read about Smart Vision Labs in "Business Insider" 09/29/14 [http://www.businessinsider.com/sc/smart-vision-labs-changing-vision-care-2014-9] * PIKE Ophthalmic, image.[https://web.archive.org/web/20151222105214/http://pikeophthalmic.com/]
Category:Ophthalmology Category:Ophthalmic equipment