NCLE Exam Prep with Complete Solutions!

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 edge of the lens to the opposite edge curve widths - ANSWER-the width of the CPC, PPC, or IPC central thickness - ANSWER-separation between the anterior and posterior surface at the geometric center of the lens. minus lenses are thinner, plus lenses are thicker ballasted lens - ANSWER-lens with a heavier base which becomes oriented inferiorly or downward when the lens is worn prism ballated lens - ANSWER-a ballasted lens which utilizes a prism wedge designed to weight the lens truncated lens - ANSWER-a lens which has been cut off, usually 0.5-1.5 mm along its lower edge, to form a horizontal base. double ________ along the top and bottom portion of the lens is sometimes done to help improve stabilization back surface power - ANSWER-effective power of a lens when measured from the back surface