optic zone -Answer✅the central portion of a contact lens which contains the refractive power and generally corresponds to the central corneal cap posterior apecal radius -Answer✅this term is generally used in reference to spin-cast soft lenses. the curvature of the posterior surface of the lens changes with the refractive power. the radius of curvature is measured at the apex of the posterior surface. steeper base curve -Answer✅ occurs when the posterior radius of curvature is decreased (i.e. 8.4 to 8.1 mm) flatter base curve -Answer✅occurs when the posterior radius of curvature is increased (i.e.8.1 to 8.4 mm) bicurve lens -Answer✅a contact lens which contains two curves: one base curve and one secondary curve. it is usually small 7.5 to 8.8 mm on diameter, relatively steep and made with narrow peripheral curves about 0.2 mm. lenses are usually intrapalpebral lenses, designed to fit within the palpebral fissure limits. tricurve lens -Answer✅a contact lens which contains three curves: a base curve, an outer peripheral posterior curve (PPC), and an intermediate posterior curve (IPC). lenses are generally larger, 9.5 mm or greater. multicurve lens -Answer✅contains a base curve and three or more peripheral curves. usually a larger lens. junctional zone -Answer✅the junction of two curves blending -Answer✅the smoothing of a junctional zone by removing the sharp line between the zones lens diameter or chord diameter -Answer✅the width of a lens or the measurement from one