According to ANSI, what is the tolerance for cylinder power above 4.50D?

The correct answer pertains to the standards set by the American National Standards Institute (ANSI) regarding the tolerance for cylinder power in corrective lenses. When the cylinder power exceeds 4.50 diopters (D), ANSI specifies that the acceptable tolerance is ± 0.10 D.

In practical terms, this means that if a prescription states a cylinder power of, for example, 5.00 D, the actual power measured in the lens should fall within the range of 4.90 D to 5.10 D to meet ANSI standards. The importance of understanding these tolerances is paramount for ensuring that patients receive lenses that accurately reflect their prescribed vision correction needs.

Although other percentages, such as 2%, 3%, and 5%, are common tolerances in different contexts or for other parameters (like overall power), they do not apply to cylinder power above 4.50 D according to ANSI guidelines. The specified tolerance of 4%, therefore, is crucial for ensuring proper vision correction and aligning with standard practices in the optician field.