Prism correction

A lens which includes some amount of prism correction will displace the viewed image horizontally, vertically, or a combination of both directions.

Other applications include yoked prism where the image is shifted an equal amount in each eye.

[1] Individuals with nystagmus, Duane's retraction syndrome, 4th Nerve Palsy, and other eye movement disorders experience an improvement in their symptoms when they turn or tilt their head.

Yoked prism can move the image away from primary gaze without the need for a constant head tilt or turn.

Prism dioptres are represented by the Greek symbol delta (Δ) in superscript.

An additional use of the rule is for determining the amount of unprescribed prism that is introduced if the lens is not correctly centred on the wearer's pupil.