Related Experiment Video
Updated: Aug 20, 2026

Correction of Presbyopia by Monocular Bi-Aspheric Ablation Profile
Published on: September 20, 2024
A bitoric rigid contact lens with base down prism to eliminate binocular vertical diplopia
Richard G Lindsay1, Gerard W Crock
1Department of Optometry and Vision Sciences, The University of Melbourne, Australia.
Abstract:
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.
Related Concept Videos
Focusing of Light in the Eye
Open Angle Glaucoma: Treatment
Drugs such as carbonic anhydrase inhibitors, α2- and...
Depth Perception and Spatial Vision
Angle Closure Glaucoma: Treatment
