Vertometer

A vertometer is an ophthalmic bench instrument used to measure diopter power of a lens. It differs from a lensmeter or lensometer which is a general dispensary tool for opticians to verify spectacle prescriptions at the laboratory. A vertometer, on the other hand, is a more precision instrument used to locate, mark, and index a lens optical center for edging, mounting, and construction of a spectacle prescription.

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History naming the precision instrument

The theory of geometrical optics uses ray tracing techniques. In many of his models, Galileo used a mathematical formula that measured a vertex distance. This nomenclature prevailed throughout hundreds of years, during a time that studies of optics may have been misunderstood. Derived from the word, the measure of the focal length of a lens is represented by the reciprocal of the vertex distance in meters, or diopters. Vertometers measure sphere ± cylinder x axis, and can be used to calculate prismatic power by indexing the optical center offset from the visual axis. An ink coated stylus is used to mark optic centers on the lens in the optical laboratory. A millimeter rule would be nearby for spectacle eyesize fittings.

See also

• Aspheric lens
• Diopter
• Lens clock
• Vertex

References

• Bausch & Lombe Model 70 (includes picture of instrument)