Glossary NCLE Exam Questions & Answers 100% Accurate

Accommodation - ANSWER-The ability of the crystalline lens to adjust power to provide retinal focus of images of objects closer than optical infinity Aphakia - ANSWER-Absence of the crystalline lens. Astigmatism - ANSWER-A refractive defect where the refractive surface has different power in different meridians As a result the image formed of a point object will not be a point but a line Axis (cylinder) - ANSWER-The weakest or least curved meridian on the surface of a cylindrical or toric surface Axis (principal) - ANSWER-An imaginary line going through the geometric center of an optical system perpendicular to the surface. Base Curve - ANSWER-Of a contact lens the curvature of the posterior optical portion otherwise known as the Posterior Central Curve Cylinder - ANSWER-An object whose surface is curved differently in different meridians with the axis having zero curvature Cylinder Lens - ANSWER-A lens with different power in different meridians due to one or more surfaces having cylindrical or toric shape Cylinder Power - ANSWER-The algebraic difference in power between the principal meridians of a cylinder lens Diopter - ANSWER-A unit of measurement equal to the reciprocal meter used to measure vergence of light and power of optical lenses Dispersion - ANSWER-The separation of white light into its spectral colors Effectivity - ANSWER-Changes in the vergence of light between one point and another In contact lens practice this change is most often observed when the position of the correcting lens is moved from the spectacle plane to the corneal plane Focal Length - ANSWER-The distance from the vertex of an optical surface to its focal point The reciprocal of the focal length is the power