prism /priz″əm/ [Gk, prisma, that which is seen through] , 1. a solid of glass, plastic, or a similar substance with a triangular or polygonal cross section, which splits up a ray of light into its constituent colors and turns or deflects light rays toward its base. Prisms are used to correct deviations of the eyes because they alter the apparent situation of objects. 2. enamel prism, or calcified rods, surrounded by organic prism cuticle joined together to form tooth enamel. 3. an adverse prism or verger prism used to test and train ocular muscles.
