How Prism Correction Works

Prism correction is used in eyeglasses to correct vision disorders by redirecting light from landing on one part of the eye into landing on a different part of the eye.

Method

• Prisms are placed within the lenses of eyeglasses that refract light and change the location upon which images land in the eye. Prisms provide minor adjustments to the image being seen by a single eye.

Measurements

• Prisms are measured using diopeters. One diopeter equals the amount of prism power necessary to divert a ray of light one centimeter from a light-emitting distance of one meter from the prism.

Uses

• Prisms are used in eyesight correction for individuals who have conditions that result from their eyes not being perfectly aligned (such as those with strabismus) that cause double images and blurred vision.

Placement

• The prism must be placed in a certain area using the terms "base-down," "base-in," "base-up," and "base-out" that determine which direction in the lens the base of the prism will face. Often, multiple prisms will be used to divert light into the correct area.