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Revisions to tolerances in cylinder axis and in progressive addition lens power in ANSI Z80.1-2005.

Brown WL

Division of Optometry, Department of Ophthalmology, Mayo Clinic, Rochester, Minnesota 55905, USA. brown.william2@mayo.edu

BACKGROUND: ANSI Z80.1 (American National Standards Institute) is a voluntary standard that provides tolerance guidelines for ophthalmic lens parameters. The recently approved ANSI Z80.1-2005 changes tolerances for cylinder axis for all ophthalmic lenses and for distance power for progressive addition lenses (PALs). METHODS: The ANSI Z80.1 committee analyzed the amount of unwanted residual cylinder created by rotating a cylinder axis away from its desired orientation for a range of cylinder powers. The limits of axis orientation error that keep the residual unwanted cylinder error within the tolerances for cylinder power were determined. For PALs, a tolerance for distance power error was sought that considers the currently followed standards for front surface power error and the tooling steps used for the rear surface. RESULTS: Tolerances for cylinder axis error were changed to +/-14 degrees for 0.25 diopter (D) cylinders and to +/-7 degrees for 0.50 D cylinders. Tolerance for error in back vertex power of PALs was changed to +/-0.16 D for both sphere and cylinder. CONCLUSION: Tolerances for cylinder axis for low cylinders have been made in ANSI Z80.1-2005 to be consistent with tolerances in cylinder power. Changes in tolerance for power errors in PALs have been made to recognize fabrication challenges.

Published 3 July 2006 in Optometry, 77(7): 343-9.
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