{{For|the instrument to verify the correct prescription in a pair of eyeglasses|focimeter}}
A '''focometer''' is an instrument that measures refractive errors and is intended to provide spherical eyeglass prescriptions to rural or economically 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 scale.
The focometer was developed by Drs. Ian Berger and Larry Spitzberg at the University of Houston College of Optometry in Houston, 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 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, 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