Tolerance analysis of progressive addition lenses

The progressive addition lenses(PAL) have been used widely because of the advantage which can meet the requirements of distant and near vision both at the same time.The basic structure,design and evaluation method of progressive addition lenses were introduced. Based on the national standard that the difference between actual diopter and theoretical value should be less than 0.1 m-1 within the lens effective area, the tolerance analysis of progressive addition lenses was realized.The tolerance formula related to diopter and surface was derived from the surface equation and sphere equation. As an example,a progressive addition lens with 2.5 m-1 addition (6.5 m-1~9 m-1) was designed and evaluated, the tolerance was analyzed. The analysis result shows that tolerance value should be less than 0.1 m at the most sensitive area of lens surface, which provides theoretical basis for the control precision of lens processing.