Hill Richard M. O.D. Ph.D.Cornea: 1990 Original Article: PDF Only Buy Abstract Three indices of oxygen passage exert considerable influence in contact lens practice: (a) Dk/L, which indicates the oxygen transmissivity of a lens; (b) equivalent oxygen percentage (EOP), which assesses corneal oxygen demand during lens wear; and (c) pachometry, a measure of the swelling response of the cornea to lens-induced hypoxia. These indices correlate well with one another but reflect different “time-line” values, with Dk/L and EOP giving predictive information about lens-eye interactions and pachometry reflecting actual wearing responses. Lens oxygen data hold tangible benefits for manufacturers, clinicians, and patients. They guide manufacturers in choosing which new lens materials to develop, in making decisions about physiologically acceptable lens thicknesses, in affirming safety and efficacy data, in securing Food and Drug Administration (FDA) product approval, and in presenting performance information to doctors and patients. Used effectively, such guidance should lower the cost of product development. Clinicians use lens oxygen ratings to refine their prescribing practices, thereby boosting patient satisfaction and lens wear success. Besides favoring long-term ocular health, oxygen ratings may yield an economic benefit for patients, if the savings realized by manufacturers during product development are translated into lower lens prices. © Lippincott-Raven Publishers.