NAO VOLUME 1: DISPENSE AND LAB TERMS
COMPLETE QUESTIONS AND ANSWERS WITH
VERIFIED SOLUTIONS!
A measurement - ANSWER Refers to the horizontal boxed measurement of a
frame or lens
Abaxial - ANSWER Situated out of or directed away from the axis
Aberration - ANSWER An imperfection in a lens or optical system which
prevents a point focus
Addition (add) - ANSWER The reading addition is the amount of plus power in
the segment of a bifocal lens. In trifocals lenses and lenses for special purposes,
segments are used for purposes other than reading and the segment power is
referred to as an "intermediate addition" or a "minus addition" as the case may be.
Ametropia - ANSWER A general term applied to that condition of the eye in
which there is an error of refraction of any kind
Apex - ANSWER The thin edge of a prism
Aspherical - ANSWER Not spherical, used to reduce marginal aberration, such
conic sections as parabolic, hyperbolic, or ellipsoidal, a lens surface having an
infinite number of curves with different radii
,Astigmatism - ANSWER A defect of an optical system such as a lens or eye.
Light rays from one point of an object are not brought to a single image point. This
causes imperfect image formation or indistinct vision.
Axis - ANSWER The orientation of a cylindrical lens in a frame. The line
passing through the optical center perpendicular to the cylinder of the lens surface.
The meridian of no power of the cylinder.
Axis drum - ANSWER Locating device on the vertometer for measuring the
axis of a lens
B measurement - ANSWER The vertical boxed measurement of a lens or frame
Back focal length - ANSWER Distance from back vertex to the secondary
focus
Back vertex distance - ANSWER The measurement from the back surface of a
lens to its focal point or it's reciprocal is the measurement of the power of a lens in
diopters
Base - ANSWER The thick edge of a prism
Base curve - ANSWER More accurately, the front base curve is the curve that
is associated with the front surface power of a lens blank. In a cylindrical lens,
there will be a back base curve, which is the weakest curve on the back surface
(ocular surface) of the lens.
Beam - ANSWER A group of parallel rays of light
, Bent lens - ANSWER A term to distinguish the form of curved lenses such as
periscopic, meniscus, or Toric lenses, from a flat lens of the same power
Bevel - ANSWER The edge design of a lens so that it will remain in the eye
wire of a frame
Biconcave - ANSWER With 2 concave surfaces
Biconvex - ANSWER With 2 convex surfaces
Bifocal - ANSWER With 2 focal lengths. A bifocal lens is, in effect, 2 lenses
joined together to obtain in a single lens an area for distance vision and an area for
near cision
Blocking - ANSWER Attaching lenses to a blacking body in position for
surfacing. Blocking is usually done with a metal alloy
Boxing system - ANSWER A method to measure the size of lenses or frames
whereby the outline of a lens is enclosed in a rectangle whose sides are tangent to
the farthest point of the lens or frame at top, bottom, and sides
Caliper - ANSWER Thickness gauge for lenses
Cataract - ANSWER The condition of the eye in which the crystalline lens
loses its transparency and obstructs the passage of light
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