Application of the aniseikonic ellipse to prisms.

The aniseikonic ellipse is derived from the meridional magnification effects of the two eyes on a circular object and represents the aniseikonic ratio in all meridians. It facilitates the analysis and prediction of aniseikonic space distortions. This study shows how the concept can be applied not only to lens magnification but also to the distortion and nonuniform magnification produced by prisms. Since prism images of a circle are asymmetrical, the corresponding aniseikonic "ellipse" is also asymmetrical. Moreover, its dimensions will vary with the nonuniform magnification across the prism. However, for small portions of the prism field it can be used conventionally as for lenses. In addition, the nonlinear binocular distortions occurring over larger portions of the field can be derived from the aggregate effect of representative aniseikonic ellipses in the various portions of the prism.