A bitoric rigid contact lens with base down prism to eliminate binocular vertical diplopia.

Prism base down can be incorporated into a rigid gas permeable contact lens to align the diplopic images in a patient who has a significant vertical phoria. A rigid lens may also incorporate both vertical base down prism and a toroidal back surface - the vertical prism to correct the heterophoria and the toric back surface to improve the physical fit of the lens on a highly toric cornea. This paper presents a case where vertical diplopia due to a post-surgical left hyperphoria of about four prism dioptres was eliminated by the incorporation of the appropriate amount of base down vertical prism into a bitoric rigid gas permeable contact lens.