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Aberration
The failure of a refracting surface or lens to bring all rays from
an object point toward a desired image point. This can result in
image blur. Aberration also results in curvature in the image of a
straight line. It may be inherent in the lens design or may result
from an error in processing.
Accommodation
A stretching or relaxing of the eye muscles, which causes a change
in focal length of the crystalline lens, thereby producing clear
images on the retina of objects that are relatively near the eye.
Without the ability to accommodate, the image of the object would
blur.
Addition
1.
The difference in front vertex power between the reading or
intermediate portion of a multifocal lens and its distance portion.
2.
Another term for the bifocal reading segment. In this case, the
addition is a simple plus lens placed on top of a major distance
lens.
Anti-Reflection Lenses
These lenses are coated with A/R to help eliminate reflections on
the lens surface and reduce ghost images. Anti-Reflection lenses
also help reduce eyestrain caused by the lighting commonly used
office buildings and staring at computer screens for extended
periods of time. They are also one of the best remedies for the
strain caused by oncoming headlights.
Aperture
The opening in an ophthalmic frame into which a lens is inserted.
Aperture dimensions (in millimeters) do not include the depth of the
bevel groove. That principal meridian which contains only the
spherical power component of a spherocylinder lens.
Axis, optical
The straight line perpendicular to both faces of a lens along whose
path a ray will pass without being deflected. It will intersect a
spherical lens of a minus power at its thinnest point and a
spherical lens of plus power at its thickest point. If the lens has
prism power, the optical axis may lie outside the lens.
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B-dimension
A measurement of the Boxing System which measures the distance
between horizontal tangents to the bevel of a lens.
Backorder
An order placed to fill a definite order from a dispenser. Also
called short order, or special order.
Base
The finished side of a semi-finished blank. The term refers to the
curvature of the finished side. See
Curve, Base
Bevel apex
The point on the bevel of a lens.
Bifocal Lenses
Bifocal Lenses are useful in affording the patient 2 vision
corrections. One for distance and the other reading.
Bin card
A piece of paper or card stock on which the inventory, sales and
ordering of frames is recorded in the laboratory.
Blank, major
The basic lens substrate to which segments of different refractive
power may be added to produce a multifocal lens.
Blank, molded
A blank that is unfinished on both sides when it arrives from the
factory. It is used to grind lenses for non-standard prescriptions
or prescriptions that are particularly strong.
Boxing System
A system of measurement used to define various prescription
requirements relative to lens and frame dimensions.
Bridge
The supportive structural member connecting the two eyes of an
ophthalmic frame front.
Bridge, keyhole
A bridge design for a front that does not permit continuous contact
between the nose and the front in the area of the nasal crest.
Bridge, saddle
A bridge design for a front that permits continuous contact between
the nose and the front in the area of the nasal crest.
Bridge, size
The shortest horizontal distance between lenses (DBL), measured in
millimeters.
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Center, geometric
The intersection of the horizontal and vertical centerlines of a box
that circumscribes the lens shape.
Center, optical
One of the intersection points of the optical axis of a lens with
the lens surfaces. It is the point at which the lens has NO prism
power. Pure cylinder lenses have no well-defined center point since
they have no power, and therefore no prism, in one direction.
Cornea
That portion of the eye through which light rays first enter and are
bent or refracted.
Corneal reflection
Method of measuring the distance from the pupil, using light
reflected from the cornea to the center of the nose.
CRP
Abbreviation for corneal reflection pupillometer, the instrument
used to measure corneal reflection.
Crystalline lens
That portion of the eye which further refracts the light and focuses
it on the retina.
Curve, base
A manufacturer's marked or nominal surface power of a semi-finished
spherical lens or the marked minimum surface power of a
semi-finished toric lens. A semi-finished or finished lens of a
given base curve may be a part of a manufacturer's corrected curve
design series.
Curve, cross
The maximum surface power of a toric surface (90 degrees from the
base curve meridian).
Custom Lenses
Custom lenses are cataract lenses that allow patients with very bad
vision get most of their sight back along with slab off lenses that
help patients with vertical imbalance see much clearer without
double vision effect. This type of correction is called a slab-off
or bicentric grind.
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DBC
Abbreviation for Distance Between Centers.
DBL
Abbreviation for Distance Between Lenses.
Decentration
The process of moving the major reference point to a place in the
frame that is away from the geometric center of the frame.
Density
Measurement of weight based on a certain amount of material. The
weight of a lens material is reflected as its density.
Diameter, effective
A linear measurement, expressed in millimeters, equal to twice the
longest radius of an ophthalmic lens measured from its geometric
center to the apex of its edge.
Dimension
A measurement of the Boxing System which measures the distance
between vertical tangents to the bevel of a lens.
Diopter, prism
A unit of measurement used to express the angle of deviation of a
ray of light by a prism or lens. In these units, prism power is
measured in centimeters as the displacement of a light ray
perpendicular to its line of incidence at a distance of one meter.
Distance, interpupillary
The linear distance between the fixation axes of the wearer's two
eyes. It is commonly referred to as the distance between the centers
of the pupillary openings with the eyes focused on a distant object.
Distance between centers (DBC)
The horizontal linear distance between geometric centers of the two
eyes of a frame front.
Distance between lenses (DBL)
The minimum horizontal distance between lenses, as measured at the
apices of their bevels.
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ED
Abbreviation for effective diameter.
Effective diameter
Defines the minimum lens that will fit a frame when the geometric
center of the lens is exactly centered in the frame.
Eye
See
Eyewire.
Eye, emmetropic
Another name for the normal eye, one that does not need corrective
lenses.
Eye, hyperopic
Farsighted eye, cannot focus on objects that are close up. This eye
may be thought of as optically shorter than it should be.
Eye, left
The aperture in front of the wearer's left eye, as worn.
Eye, myopic
Nearsighted eye, unable to focus well on items that are in the
distance.
Eye, right
The aperture in front of the wearer's right eye, as worn.
Eye size
See
Lens size.
Eyeglasses
A term commonly used to describe an ophthalmic frame with lenses
inserted.
Eyewire
The component of an ophthalmic frame front which encircles one lens.
Also called an eye.
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Focimeter
An instrument used to determine vertex power, axis location, optical
center, and major reference point location and prism power at a
given point on an ophthalmic lens.
Former
See
Pattern, lens.
Frame (ophthalmic or spectacle)
A device for holding ophthalmic lenses in the proper position on the
head in front of the eyes. A frame typically consists of a front
that holds the lenses, and a pair of temples (earpieces) that secure
the unit to the head.
Frame, combination
A frame whose front consists of a metal chassis with attached trim
parts (sometimes known as top rims). These trim parts are typically
plastic, aluminum or other metal, and are attached to the top
portion of the chassis. These top rims may serve functional or
cosmetic purposes, or both
Frame, dress ophthalmic
A frame for prescription or corrective lenses, intended for ordinary
use in correcting or improving vision. Such a frame is not intended
for occupational or safety use.
Frame, rimless
A type of frame that provides no, or only partial, peripheral
support for the lenses.
Frame, zyl
A frame made from cellulose acetate.
Front
A component of an ophthalmic frame, typically consisting of a bridge
and eyewires.
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GC
Abbreviation for geometric center.
Glazed
Assembled with appropriate ophthalmic lenses.
Groove, eyewire T
The recessed area of an eyewire in which the lens edge is seated,
also called the lens groove.
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Hinges
Part of the hardware of the frame. The hinges attach to both the
temple and front of the frame.
High index lenses
Lenses made with a higher refractive material than CR-39 plastic or
glass. High Index Lenses are thinner than lower index lenses.
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IPD
Abbreviation for interpupillary distance.
Index of refraction
A measure of the ability of a lens material to refract a ray of
light of a given wavelength. This is usually stated for the
wavelength of the helium d-line (587.56 nanometers). The higher the
index, the more the refractive power of the lens. For the ophthalmic
glasses most commonly in use, n=1.5230. The index of refraction for
allyl resin, a plastic most commonly used for eyeglasses, is
typically 1.4975.
Intermediate
That area in a trifocal lens or blank which has been designed to
correct vision at ranges intermediate to distant and near objects.
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Lens, bifocal
A lens designed to provide correction for two viewing ranges.
Lens, concave
See
Lens, minus
Lens, converging
See
Lens, plus
Lens, convex
See
Lens, plus
Lens, corrected curve
A lens that has been designed to reduce peripheral power errors for
the conditions of intended use over a specified portion of the field
of view.
Lens, cylinder
A special case of the spherocylinder lens in which one of the
principal meridians has zero refractive power.
Lens, crystalline
That portion of the eye which further refracts the light and focuses
it on the retina.
Lens, diverging
See
Lens, minus
Lens, edged
A lens whose periphery has been ground (flat, beveled or grooved) to
a specific size and shape.
Lens, fused
A multifocal lens made from three or more pieces of glass which are
thermally sealed together. On fused multifocal lenses, curve changes
or ledges are invisible.
Lens, laminated
A lens constructed as a sandwich of multiple layers of glass or
plastic, or both, bonded together to form a single unit.
Lens, lenticular
A lens, usually of a strong refractive power, in which the
prescribed power is provided over only a limited central region of
the lens, called the lenticular portion. The remainder of the lens
is called the carrier and provides no refractive correction but
gives dimension to the lens for mounting.
Lens, minus
A lens having negative dioptric power. It is thinner at the center
than at the edge.
Lens, multifocal
A lens designed for two or more viewing ranges, for example, bifocal
or trifocal lenses.
Lens, one-piece multifocal
A multifocal lens or a blank fabricated from a single piece of glass
or plastic.
Lens, pattern
A cam, or template, used in lens edging equipment to generate the
correct peripheral shape and geometric center location. Also called
a lens former.
Lens, photochromic
A lens that darkens in response to the ultraviolet component of
sunlight.
Lens, plano
A lens which has zero refractive power.
Lens, plus
A lens that has positive refractive power. It is thicker at the
center than at the edge.
Lens, progressive power
A lens that is designed to provide correction for more than one
viewing range in which the power changes continuously rather than
discretely.
Lens, semi-finished
A lens that has only one surface finished.
Lens, single-vision
A lens designed to provide correction for a single viewing distance.
Lens, spherical
A lens that has the same refractive power in all meridians. Such a
lens may have rotationally symmetrical aspheric (reflective)
surfaces.
Lens, sphero-cylinder
A lens that has different refractive power in the two principal
meridians. It is often referred to as an astigmatic or toric lens
and sometimes incorrectly referred to as a cylinder lens.
Lens, stock
A lens supplied by a manufacturer with both surfaces finished and a
specific back vertex power or powers. Such a lens has yet to be
edged to a specific shape. Also known as factory finished, uncut.
Lens, toric
A lens which has two distinct curvatures, at right angles (90
degrees) to each other. See
Lens, sphero-cylinder.
Lens, uncut
A lens with finished optical surfaces on both sides but not edged
for mounting in a frame.
Lens measure
An instrument that is used to measure surface curvature. Also called
sagitta gauge, or lens clock.
Lens size
The horizontal box dimension (A-dimension) of a finished lens. Also
called eye size.
Line, geometric center
A horizontal line running through the geometric center of a lens.
Also called normal mounting line.
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MPD
Abbreviation for monocular pupillary distance.
Major reference point
The point on a lens at which the specified distance prescription
requirements shall apply (commonly but imprecisely referred to as
the optical center).
Meridian
The line of intersection of a surface with a plane perpendicular to
that surface at a specified point. When applied to a lens, it also
may be defined as a plane that contains the optical axis.
Meridians, principal T
The two mutually perpendicular meridians of a sphero-cylinder lens
or toric optical surface with minimum and maximum power.
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OD
Latin abbreviation meaning right eye.
OU
Latin abbreviation meaning both eyes.
OS
Latin abbreviation meaning left eye.
Order form, prescription
Order form that originates with the customer. It gives the name of
the doctor, the name of the patient, and a description of the
desired product.
Order form, stock
Order form that is sent by the dispenser to the laboratory. The form
is used to replenish the dispenser's stock.
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PD
Abbreviation for interpupillary distance.
Packing slip
The slip of paper found inside the cartons which come from the
manufacturer. The packing slip may list a description of the item,
the quantity ordered, quantity shipped, and the code number as well
as the name and address of the manufacturer.
Photochromic Lenses
Photochromic lenses change from light to dark through changing
levels of sunlight. "Transitions 3" are the state of the art in the
Photochromic category of lenses. When worn indoors they are
virtually clear, when worn outside they change to a dark color.
Polarized Lenses
Polarized Lenses block out virtually all Ultra Violet Rays. These
lenses help to eliminate haze and glare, while increasing
visibility. Colors appear more vibrant while others are subdivided
to give the wearer true view without the irritating sun. Excellent
for driving!
Polycarbonate Lenses
Polycarbonate Lenses are the most durable of all lenses. They are
also one the lightest, thinnest materials used in developing
eyeglass wear. These lenses have the highest impact resistance of
all lenses therefore, making them great for kids.
Power, cylinder
The difference (plus or minus) between the powers measured in the
two principal meridians of a lens.
Progressive Lenses
Progressive lenses are state of the art boasting an infinite number
of corrections. No-line bifocals have been round for over 20 years
with major improvements taking place yearly. The progressive
multifocals have a distance viewing area in the upper area of the
lens, down to where the near correction begins. Major benefits of
the lens is the lack of image jump on the segline.
Power, marked surface
The nominal curve of a semi-finished lens marked in diopters, as
expressed by the manufacturer. The difference between marked and
actual tool curve of the surface represents the manufacturer's
compensation for that base curve. This compensation allows standard
tooling to be utilized over a range of prescriptions with little or
no further compensation required by the laboratory to produce
accurate vertex powers.
Power, meridional
The refractive or surface power of a lens measured in a specified
meridian.
Power, nominal
See
power, marked surface.
Power, prism T
The deviation of a light ray produced by a prism or by the prismatic
component in a lens, expressed in prism diopters.
Power, refractive
The ability of a lens or an optical surface to produce a change in
the convergence or divergence of a beam of light, usually expressed
in diopters.
Power, sphere
In a spherical lens, the dioptric power of the lens. In a sphero-cylinder
lens, the sphere power is located in the cylinder axis meridian.
Power, surface refractive (R)
The refractive power of a lens surface having index of refraction
(n) is a measure of its ability to refract light, and is expressed
in diopters. The expression relating (R) to (S) and (n) is:
R=[(n-1)S]/0.530 Since common ophthalmic materials do not have
indices of refraction equal to 1.530, there is not a one-to-one
correspondence between surface tool power (S) and surface refractive
power (R). For example, common ophthalmic glass has an index of
refraction of 1.5230. Therefore, a one-diopter surface tool will
produce a surface refractive power (R) of 0.987 diopter. Surface
refractive power is also called true power.
Power, surface tool (S)
The actual radius of curvature of a tool or the surface it produces.
By common usage in the United States, a tool with a radius of
curvature of 530mm will produce a surface tool power (S) of one
diopter. When (r) is the radius of curvature in millimeters, then S
= 0.530/(0.001r).
Power, vertex
The inverse of the distance, expressed in meters, from the lens
vertex to the corresponding focal point. This is expressed in
diopters. In a prescription, the spherical component of power and
cylindrical component are always expressed in terms of rear (or
back) vertex power. Focimeters are designed to measure vertex power
directly.
Pupillary distance, binocular
The measurement between the patient's pupils, expressed in
millimeters. Also called IPD.
Pupillary distance, monocular
The measurement from the center of the nose to the pupil. Also
called MPD.
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Reading Glasses
Reading Glasses have lenses with stronger powers because they
incorporate both the distance and near powers to concentrate power
for easy reading for the wearer.
Refraction
The bending of light rays caused by prisms and lenses. See
power,
refractive.
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Sagitta
See
vertex depth.
Segment
A specified area of a multifocal lens having different power from
the major portion. This also may refer to the actual piece of
material added to the lens in the case of a fused or cemented
multifocal lens. Also called the addition.
Short order
See
Backorder.
Spectacle
An ophthalmic device consisting of two ophthalmic lenses and a
supporting frame to position and retain the lenses in proper optical
alignment with the eyes.
Sun Lenses
Sun Lenses are lenses that have a mirror coating and are usually
very dark in appearance. These lenses help reduce light transmission
and come in many colors such as yellow, blue, mirror etc.
Surface, aspheric
A nonspherical surface curvature commonly used to improve optical
performance, particularly for high refractive powers. Such
curvatures are often derived from the oblique intersection of a
plane and a conical surface, and are referred to as "conoids" or
"conic" sections.
Surface, plano
A flat surface having zero surface power, or an infinite radius of
curvature.
Surface, spheric
A curved surface having the same radius of curvature in all
meridians.
Surface, toric
A surface in the form of a torus having different powers in two
principal meridians. The shape may be visualized as that of a
section cut from a doughnut or from a football-shaped surface.
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Temple,
library
The style of temple that has almost no bend over the ear; it was
originally designed for ease of removal.
Temple,
riding bow
A style of temple which bends around to hug the ear. It is
particularly useful to people whose jobs are very active, or for
small children.
Temple, skull
A style of temple that has a slight bend which allows the frame to
fit easily over the ear, and to hug the head lightly.
Temple,
spatula
Another term for skull temple; also called paddle temple.
Temple
screws
Tiny screws which connect the front and temple halves of the hinges.
Thickness, center
The thickness of a lens at the major reference point.
Transitions Lenses
The leader in plastic photochromic lenses to the industry.
Transitions continue to develop the technology for changing lenses.
Transposition
Changing the powers of a sphero-cylinder lens or astigmatic
prescription from one cylinder form to the other (- to + or + to -).
Trifocal Lenses
Trifocal lenses are useful in affording the patient 3 vision
corrections. One for distance, intermediate (arm length) and
reading.
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Varilux Lenses
The leader in progressive line-free bifocals for over 20 years.
Varilux continues to lead this category and this year introduces the
Panamic lens which will give the patient an even more
enhanced vision correction.
Vertex depth
The depth of the surface curve on a lens measured over a specific
diameter. Also called the sagitta.
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Wave
A local ripple-like irregularity in a lens surface.
Zyl
Cellulose acetate, used to make frames.
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