A measurement - correct answer ✔✔Refers to the horizontal boxed measurement of a frame or lens
Abaxial - correct answer ✔✔Situated out of or directed away from the axis
Aberration - correct answer ✔✔An imperfection in a lens or optical system which prevents a point focus
Addition (add) - correct 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 - correct answer ✔✔A general term applied to that condition of the eye in which there is an
error of refraction of any kind
Apex - correct answer ✔✔The thin edge of a prism
Aspherical - correct 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 - correct 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 - correct 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 - correct answer ✔✔Locating device on the vertometer for measuring the axis of a lens
, B measurement - correct answer ✔✔The vertical boxed measurement of a lens or frame
Back focal length - correct answer ✔✔Distance from back vertex to the secondary focus
Back vertex distance - correct 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 - correct answer ✔✔The thick edge of a prism
Base curve - correct 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 - correct answer ✔✔A group of parallel rays of light
Bent lens - correct 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 - correct answer ✔✔The edge design of a lens so that it will remain in the eye wire of a frame
Bifocal - correct 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 - correct answer ✔✔Attaching lenses to a blacking body in position for surfacing. Blocking is
usually done with a metal alloy
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