Fig 2. A Fresnel prism, much thinner than a conventional ophthalmic prism of the same power, can be imagined to be a series of small plastic prisms (see shaded prisms) lying adjacent to each other on a thin platform of plastic. (Modified from Jampolsky A, Flom MC, Thorson JC: Membrane Fresnel prisms: A new therapeutic device. In Fells P (ed): Proceedings of the First Congress of the International Strabismological Association. London: Kimpton, 1971.)