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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 dispensory tool for opticians to verify spectacle prescriptions at the laborartory. 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.

History

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.

See also

• Aspheric lens
• Diopter
• Galileo
• Lens clock
• vertex

References

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

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