# Focometer

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{{For|the instrument to verify the correct prescription in a pair of eyeglasses|focimeter}}

A '''focometer''' is an instrument that measures [refractive error](/source/refractive_error)s and is intended to provide spherical [eyeglass prescription](/source/eyeglass_prescription)s to rural or [economically disadvantaged](/source/Disadvantaged) populations without the need for complicated protocols, expensive equipment, or electricity.<ref name=catinist>{{cite journal |vauthors=Berger IB, Spitzberg LA, Nnadozie J |title=Testing the Focometer—A new refractometer |journal=Optom Vis Sci |volume=70 |issue=4 |pages=332–8 |date=April 1993 |pmid=8502463 |doi=10.1097/00006324-199304000-00013 |issn=1040-5488}}</ref><ref name=Infocus/> The focometer is monocular and hand-held, and is normally used in natural lighting. Patients rotate a collar on the focometer until the best focus is achieved.<ref name=Infocus>{{cite web |url=http://www.infocusonline.org/focometerfactsheet_print.html |title=The focometer fact sheet |work=Infocusonline |accessdate=26 August 2008}}</ref><ref name=medcentral>{{cite journal |journal=Community Eye Health |date=29 November 1999|volume=12 |issue=31 |pages=43 |title=The focometer: use in aphakic correction |first=GVS |last=Murthy |author2=Johnson, G.J. |pmc=1706012 |pmid=17491998 }}</ref>  The individual's refractive power is then read off a linear [dioptre](/source/dioptre) scale.

The focometer was developed by Drs. Ian Berger and Larry Spitzberg at the [University of Houston College of Optometry](/source/University_of_Houston_College_of_Optometry) in [Houston, Texas](/source/Houston%2C_Texas), to provide a simple, inexpensive means for measuring refractive error in human vision. The portable, hand-held instrument is highly appropriate for use in remote and poor areas.

Focometers measure spherical refractive errors. [Astigmatism](/source/Astigmatism_(eye)) can also be measured using a "clock target" with the device.<ref name=Infocus/> A study has found, however, that the focometer is less effective for identifying astigmatism than an [autorefractor](/source/autorefractor), and that its axis accuracy is limited to 15°.<ref name=cat/>

The advantages of a focometer over other methods for use in developing countries are that it is lightweight, compact, relatively inexpensive, fairly quick, and easy to use with minimal training. A clinical trial compared the repeatability, validity, and ease of use of the focometer with an autorefractor.<ref name=cat>{{cite journal |vauthors=du Toit R, Soong K, Brian G, Ramke J |title=Quantification of refractive error: comparison of autorefractor and focometer |journal=Optom Vis Sci |volume=83 |issue=8 |pages=582–8 |date=August 2006 |pmid=16909083 |doi=10.1097/01.opx.0000230270.39804.54 }}</ref> It found that the focometer results were within 0.75 dioptres of the autorefractor value 84% of the time. The authors found that repeatability of the measurements improved when patients were allowed to "practice" twice on each eye before taking the real reading.

==References==
{{Reflist}}

Category:Ophthalmic equipment

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