Wikiversity, Youtube and Archive.org.A<unk>  in an Optical shop A simple<unk>  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<unk>  or<unk> , also known as a focimeter or vertometer, is an ophthalmic instrument. It is mainly used by optometrists and opticians to verify the correct prescription in a pair of eyeglasses, to properly orient and mark uncut lenses, and to confirm the correct mounting of lenses in spectacle frames.<unk> s can also verify the power of contact lenses, if a special lens support is used. The parameters appraised by a<unk>  are the values specified by an ophthalmologist or optometrist on the patient's prescription: sphere, cylinder, axis, add, and in some cases, prism. The<unk>  is also used to check the accuracy of progressive lenses, 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 to obtain the last prescription the patient was given, in order to expedite the subsequent examination.
Lensmeter
Pupilometer
Focometer
Eye chart
Esthesiometer
Exophthalmometer
Campimeter
Intraocular pressure