Even when there is no anisometropia, dynamic aniseikonia is often induced by unequal prismatic effect. This can happen with frames with a high degree of face form angle and prescribed prism.
The effect of a face form angle is to induce base in prism in lateral gaze with near-sightedness (the eyes are forced to diverge) and Base Out prism with far-sightedness (the eyes are forced to converge).
Prescribed prism (e.g., base up in one eye and base down in the other) will create an opposing curvature of image due to the nonlinearity of the prismatic effect because of a differing optical path length caused by the prism, thus creating a pincushion effect at the prism apex.
The SHAW™ lens gives the optometrist a tool to manage distortions and improve the comfort of wear.