GLOSSARY NCLE EXAM – QUESTIONS & ANSWERS
Accommodation - Correct answer- The ability of the crystalline lens to adjust power to provide retinal
focus of images of objects closer than optical infinity
Aphakia - Correct answer- Absence of the crystalline lens.
Astigmatism - Correct 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) - Correct answer- The weakest or least curved meridian on the surface of a cylindrical or
toric surface
Axis (principal) - Correct answer- An imaginary line going through the geometric center of an optical
system perpendicular to the surface.
Base Curve - Correct answer- Of a contact lens the curvature of the posterior optical portion otherwise
known as the Posterior Central Curve
Cylinder - Correct answer- An object whose surface is curved differently in different meridians with the
axis having zero curvature
Cylinder Lens - Correct answer- A lens with different power in different meridians due to one or more
surfaces having cylindrical or toric shape
Cylinder Power - Correct answer- The algebraic difference in power between the principal meridians of a
cylinder lens
Diopter - Correct answer- A unit of measurement equal to the reciprocal meter used to measure
vergence of light and power of optical lenses
, Dispersion - Correct answer- The separation of white light into its spectral colors
Effectivity - Correct 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 - Correct answer- The distance from the vertex of an optical surface to its focal point The
reciprocal of the focal length is the power
Focal Point - Correct answer- The point along the principal axis of an optical surface where incident
parallel light will be focused after being converged or diverged by the surface
Focus - Correct answer- The point along the principal axis of an optical surface that light converges to or
diverges away from after encountering that surface
Image - Correct answer- An optical reproduction of an object by a lens or mirror. REAL images are
formed where converging light focuses, and VIRTUAL images are formed where diverging light focuses
Index of Refraction - Correct answer- The ratio of the speed of light in a vacuum (or air) to the speed in
another medium indicating the medium's refractive ability
Infinity (optical) - Correct answer- The distance light waves must travel from a source to lose all
curvature and be essentially parallel This distance is considered to be twenty feet
K Readings - Correct answer- Also K's The measurement of the curvature of the central cornea as
measured by the Keratometer
Keratoconus - Correct answer- A cone-shaped deformity of the cornea
Lacrimal Lens - Correct answer- The lens that is formed by the tears that collect between the base curve
of a contact lens and the anterior cornea
Accommodation - Correct answer- The ability of the crystalline lens to adjust power to provide retinal
focus of images of objects closer than optical infinity
Aphakia - Correct answer- Absence of the crystalline lens.
Astigmatism - Correct 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) - Correct answer- The weakest or least curved meridian on the surface of a cylindrical or
toric surface
Axis (principal) - Correct answer- An imaginary line going through the geometric center of an optical
system perpendicular to the surface.
Base Curve - Correct answer- Of a contact lens the curvature of the posterior optical portion otherwise
known as the Posterior Central Curve
Cylinder - Correct answer- An object whose surface is curved differently in different meridians with the
axis having zero curvature
Cylinder Lens - Correct answer- A lens with different power in different meridians due to one or more
surfaces having cylindrical or toric shape
Cylinder Power - Correct answer- The algebraic difference in power between the principal meridians of a
cylinder lens
Diopter - Correct answer- A unit of measurement equal to the reciprocal meter used to measure
vergence of light and power of optical lenses
, Dispersion - Correct answer- The separation of white light into its spectral colors
Effectivity - Correct 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 - Correct answer- The distance from the vertex of an optical surface to its focal point The
reciprocal of the focal length is the power
Focal Point - Correct answer- The point along the principal axis of an optical surface where incident
parallel light will be focused after being converged or diverged by the surface
Focus - Correct answer- The point along the principal axis of an optical surface that light converges to or
diverges away from after encountering that surface
Image - Correct answer- An optical reproduction of an object by a lens or mirror. REAL images are
formed where converging light focuses, and VIRTUAL images are formed where diverging light focuses
Index of Refraction - Correct answer- The ratio of the speed of light in a vacuum (or air) to the speed in
another medium indicating the medium's refractive ability
Infinity (optical) - Correct answer- The distance light waves must travel from a source to lose all
curvature and be essentially parallel This distance is considered to be twenty feet
K Readings - Correct answer- Also K's The measurement of the curvature of the central cornea as
measured by the Keratometer
Keratoconus - Correct answer- A cone-shaped deformity of the cornea
Lacrimal Lens - Correct answer- The lens that is formed by the tears that collect between the base curve
of a contact lens and the anterior cornea
