For cylinder axis .25 to .50, what is the tolerance degree as per ANSI?

The tolerance for a cylinder axis between .25 and .50 according to ANSI (American National Standards Institute) guidelines is indeed set at 7 degrees. This means that when measuring the axis of a cylindrical lens within this power range, the deviation from the prescribed axis should not exceed 7 degrees for the lens to meet the industry standards of accuracy.

This tolerance is crucial in opticianry as it ensures that the optical correction provided by the lenses is effective. If the axis were to deviate significantly, it could lead to less than optimal vision correction, possibly causing discomfort or visual disturbance for the wearer. In practical application, this means that opticians need to be diligent in measuring and verifying the axis of cylindrical prescriptions, particularly in this power range, to conform to these established standards.