# Lensmeter > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Lensmeter > Markdown URL: https://mediated.wiki/source/Lensmeter.md > Source: https://en.wikipedia.org/wiki/Lensmeter > Source revision: 1321920263 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) Ophthalmic instrument mainly used by optometrists and opticians A lensmeter in an optical shop A simple lensmeter cross sectional view. **1** – Adjustable eyepiece **2** – Reticle **3** – Objective lens **4** – Keplerian telescope **5** – Lens holder **6** – Unknown lens **7** – Standard lens **8** – Illuminated target **9** – Light source **10** – Collimator **11** – Angle adjustment lever **12** – Power drum (+20 and -20 diopters) **13** – Prism scale knob A **lensmeter** or **lensometer** (sometimes even known as **focimeter** or **vertometer**)[1][2] is an optical instrument used in [ophthalmology](/source/Ophthalmology). It is mainly used by [optometrists](/source/Optometrists) and [opticians](/source/Opticians) to measure the back or front vertex power of a spectacle lens and verify the correct prescription in a pair of [eyeglasses](/source/Glasses), to properly orient and mark uncut lenses, and to confirm the correct mounting of lenses in spectacle frames. Lensmeters can also verify the power of [contact lenses](/source/Contact_lenses) if a special lens support is used. The parameters appraised by a lensmeter are the values specified by an [ophthalmologist](/source/Ophthalmologist) or [optometrist](/source/Optometrist) on the patient's [prescription](/source/Eyeglass_prescription): sphere, cylinder, axis, add, and in some cases, prism. The lensmeter is also used to check the accuracy of [progressive lenses](/source/Progressive_lens), and is often capable of marking the lens center and various other measurements critical to proper performance of the lens. It may also be used prior to an [eye examination](/source/Eye_examination) to obtain the last prescription the patient was given, in order to expedite the subsequent examination. ## History In 1848, [Antoine Claudet](/source/Antoine_Claudet) produced the photographometer, an instrument designed to measure the intensity of photogenic rays; and in 1849 he brought out the focimeter, for securing a perfect focus in photographic portraiture.[3] In 1876, [Hermann Snellen](/source/Hermann_Snellen) introduced a phakometer which was a similar set up to an [optical bench](/source/Optical_table) which could measure the power and find the [optical centre](/source/Optical_centre) of a convex lens. Troppman went a step further in 1912, introducing the first direct measuring instrument. In 1922, a patent was filed for the first projection lensmeter, which has a similar system to the standard lensmeter, but projects the measuring target onto a screen eliminating the need for correction of the observer's [refractive error](/source/Refractive_error) in the instrument itself and reducing the requirement to peer down a small telescope into the instrument.[4] ## See also - [Lens clock](/source/Lens_clock) - [Optical power](/source/Optical_power) - [Diopter](/source/Diopter) - [Focometer](/source/Focometer) - [Prism dioptre](/source/Prism_dioptre) - [Corrective lens components](/source/Corrective_lens#Components_of_a_sphero-cylindrical_correction) - [Abbe refractometer](/source/Abbe_refractometer) ## References 1. **[^](#cite_ref-1)** ["Vertometer. (n.d.)"](http://medical-dictionary.thefreedictionary.com/Vertometer). *Millodot: Dictionary of Optometry & Visual Science, 7th edition*. 2009. Retrieved 2015-01-04. 1. **[^](#cite_ref-2)** ["Ophthalmology Glossary on Carl Zeiss Vision GmbH website"](https://web.archive.org/web/20080512081021/http://www.college-optometrists.org/index.aspx/pcms/site.college.What_We_Do.museyeum.online_exhibitions.optical_instruments.focimeter/). Archived from [the original](http://www.zeiss.de/de/ophthalmic/glossary_e.nsf/frameset.html?ReadForm&Redirect=/C1256E7B002D2A69/0/8BE738D3614A7DD0C1256E8200232F89) on 12 May 2008. 1. **[^](#cite_ref-3)** [Solbert, Oscar N.](/source/Oscar_Solbert); [Newhall, Beaumont](/source/Beaumont_Newhall); [Card, James G.](/source/James_Card), eds. (February 1952). ["The Focimeter"](https://web.archive.org/web/20130312194522/http://image.eastmanhouse.org/files/GEH_1952_01_02.pdf) (PDF). *Image*. **1** (2). Rochester, N.Y.: [International Museum of Photography](/source/George_Eastman_Museum) at George Eastman House Inc.: 1–2. Archived from [the original](http://image.eastmanhouse.org/files/GEH_1952_01_02.pdf) (PDF) on March 12, 2013. Retrieved June 16, 2014. 1. **[^](#cite_ref-4)** ["Focimeters"](https://web.archive.org/web/20080512081021/http://www.college-optometrists.org/index.aspx/pcms/site.college.What_We_Do.museyeum.online_exhibitions.optical_instruments.focimeter/). Archived from [the original](http://www.college-optometrists.org/index.aspx/pcms/site.college.What_We_Do.museyeum.online_exhibitions.optical_instruments.focimeter/) on 2008-05-12. Retrieved 2010-01-30. accessed 20 Jan 2009 ## External links - [Lensmeter instructional video series](https://www.youtube.com/playlist?list=PLQST6JyJD0gwQv2RVZ-b8Uo24VPIHr1B2) playlist on [YouTube](/source/YouTube_playlist_(identifier)) - [Lensometry basics](http://www.2020mag.com/ViewContent/tabid/136/content_id/395/Default.aspx) [Archived](https://web.archive.org/web/20101125164403/http://www.2020mag.com/ViewContent/tabid/136/content_id/395/Default.aspx) 2010-11-25 at the [Wayback Machine](/source/Wayback_Machine) - [The lensmeter](http://spie.org/x32360.xml) --- Adapted from the Wikipedia article [Lensmeter](https://en.wikipedia.org/wiki/Lensmeter) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Lensmeter?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.