Prismatic effect in axially symmetric spectacle lenses.

PURPOSE

The purpose of this article is to compare different approximate formulas to compute the prismatic effect in axially symmetric spectacle lenses.

METHODS

Gaussian formulas to calculate the prismatic effect are derived, for thick and thin lenses, and for near and far vision. The results from these formulas, as well as other taken from the literature, are compared with the exact results.

CONCLUSIONS

None of the studied approximations provides the most accurate results in all circumstances. The Gaussian formula for thick lenses could be considered globally the most accurate, both in near vision and far vision. However, it is notably more difficult to use than the traditional Prentice rule, because it is mathematically more complex, and needs several additional lens parameters.