New equations for determining ocular deviations produced by spectacle corrections.

Abstract

The relation between prismatic deviations at the spectacle plane and corresponding ocular deviations is demonstrated and expressed in the form of an equation. In addition, basic equations for the ocular prismatic deviations produced by spectacle lenses placed before the eyes are developed. These equations are a sequel to previous studies demonstrating that the current use of Prentice's rule for finding the prismatic effect produced by realistic spectacle lenses is not suitable for present day spectacle corrections. One set of equations is based on tangents of angles of ocular rotation, whereas another set of equations expresses ocular deviations in degrees. The former is appropriate for clinical purposes; the latter is suitable when greater accuracy is desired.