A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
aberration: A deviation
or irregularity. In this case, it refers to a visual aberration, or
a deviation from normal vision. It is 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
ablate: To remove or reshape the cornea
and correct certain vision problems.
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
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.
astigmatism: A condition of the
eye that results in blurred distance and/or near vision. The
surfaces of the eye focus the light rays at different points inside
the eye. The different points of focus create a blur of parts of
objects you see.
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
bacterial conjunctivitis: An eye infection commonly known
as pink eye; usually caused by bacteria, but may be caused by
viruses or fungi.
Base: The finished side of a semi-finished blank. The term
refers to the curvature of the finished side. See Curve,
BCVA: An acronym for Best Corrected Visual
Acuity, which is a measure of your best vision you can attain from
glasses or contact lenses.
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
Bin card: A piece of paper or card stock on which the
inventory, sales and ordering of frames is recorded in the
Blank, major: The basic lens substrate to which segments
of different refractive power may be added to produce a multifocal
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
Boxing System A system of measurement used to define
various prescription requirements relative to lens and frame
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
Bridge, size: The shortest horizontal distance between
lenses (DBL), measured in millimeters.
laser: A relatively large diameter beam (6mm - 8mm) that can be
manipulated to reshape the cornea in LASIK surgery.
cataract: A clouding of the lens
inside the eye that can cause a loss of vision.
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.
collagen: The principal
protein of the skin, tendons, cartilage, bone and connective
cornea: That portion of the eye through which
light rays first enter and are bent or refracted. The clear front
surface of the eye.
corneal flap: A thin slice of
tissue on the surface of the cornea made with a microkeratome at the
beginning of the LASIK procedure. This flap is folded back before
the laser is applied to the inner layers of the cornea.
Corneal reflection: Method of measuring the distance from
the pupil, using light reflected from the cornea to the center of
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.
DBC: Abbreviation for Distance
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
dilating: When eyes are dilated, the pupils are wider than
normal. This is accomplished by placing docops in your eyes. Your
vision will normally be blurry for up to several hours after
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
diopters: A unit used to measure the amount of
myopia, hyperopia and astigmatism of an eye. A positive number
indicates hyperopia and a negative number indicates myopia. A
negative number also is used to indicate astigmatism. The larger the
number the greater the extent of the myopia, hyperopia or
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
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
Distance between lenses (DBL) The minimum horizontal
distance between lenses, as measured at the apices of their
ED: Abbreviation for effective
Effective diameter: Defines the minimum lens that will fit
a frame when the geometric center of the lens is exactly centered in
enhancements: A follow-up procedure or retreatment. LASIK
is sometimes performed again on a patient if results were not
satisfactory after the first procedure. You should speak with your
doctor to understand this process more
epithelium: Protective layer of cells covering
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,
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.
A type of laser used in PRK or LASIK that removes tissue from the
farsightedness: Another term for
hyperopia. A condition of the eye that most commonly results in
blurred close vision although moderate to severe hyperopia may also
result in blurred distance vision. The cornea and lens focus light
rays from objects behind, rather than directly on, the
FDA: An acronym for the Food and docug
Administration. This federal agency is responsible for determining
the validity and safety of any docug, cosmetic, medical device or
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
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, docess 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
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.
GC: Abbreviation for geometric
Gaussian laser beam: A type of small-spot laser beam, its
unique rounded shape leaves the corneal surface
glaucoma: A condition usually associated with
high eye pressure. This condition results in damage to the nerve at
the back of the eye and possible loss of vision
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.
halo: A circular flare or ring
of light that may appear around a headlight or other lighted object.
This symptom may occur after surgery.
Corneal haze is a cloudiness of the normally clear cornea. Most
types of haze disappear with time or after docug treatment. Severe
corneal haze may lead to reduced visual clarity.
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.
hyperopia: Another term for farsightedness. A condition of
the eye that most commonly results in blurred close vision, although
moderate to severe hyperopia may also result in blurred distance
vision. The cornea and lens focus light rays from objects behind,
rather than directly on, the retina.
IPD: Abbreviation for
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.
Intraocular Pressure: The pressure exerted on the eye by
the fluids contained within the eye.
laser radar tracker: This type
of tracker is capable of tracking involuntary eye movements during
surgery to ensure accurate laser beam
LASIK: An acronym for Laser In-Situ
Keratomileusis. LASIK is a procedure where a device called a
microkeratome is used to surgically create a thin, hinged flap of
corneal tissue. The flap is folded back, the laser is directed to
the corneal surface exposed beneath the flap and the flap is brought
back into place.
lens: A structure inside the eye that
helps to focus light on to the back of the eye.
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
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
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
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
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
Lens, toric: A lens which has two distinct curvatures, at
right angles (90 degrees) to each other. See Lens,
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.
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).
mapping: A computerized color picture of the physical
features of the corneal surface; illustrates curves in the cornea
and how steep or flat the cornea is.
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.
microkeratome: A surgical
instrument used to cut a flap of corneal tissue as the first step in
the LASIK procedure.
misaligned flap: A condition in
which the flap created with the microkeratome has not returned to
its correct position after the procedure is complete. It is
sometimes possible to reposition the flap.
astigmatism: A condition of the eye that results in blurred
distance and near vision. The cornea and lens focus the light rays
at different points with one point focused in front of the retina
and the other point focused behind the retina. Clear vision requires
that all focus points be directly on the
myopia: Another term for nearsightedness. A
condition of the eye that results in blurred distance vision. The
cornea and lens focus light rays from distant objects in front of
the retina. This incorrect focusing of light results in blurred
images of objects at a distance.
nearsightedness: Another term
for myopia. A condition of the eye that results in blurred distance
vision. The cornea and lens focus light rays from distant objects in
front of the retina. This incorrect focusing of light results in
blurred images of objects at a distance.
OD: Latin abbreviation meaning right eye.
OU: Latin abbreviation meaning both eyes.
OS: Latin abbreviation meaning left eye.
ocular: Having to do with the
ophthalmic: Pertaining to the
ophthalmologist: A medical doctor who specializes
in the eye and is liscenced to perform surgery on the eye. All LASIK
specialists are ophthalmologists.
art and science of eye medicine.
optometrist: An eye
care specialist who specializes in the examination, diagnosis,
treatment, management and prevention of diseases and disorders of
the eye and associated structures.
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, stock: Order form that is sent by the
dispenser to the laboratory. The form is used to replenish the
overcorrection: A complication of
laser vision correction where the amount of correction is more than
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 addocess of the
Photorefractive Keratectomy: Commonly referred to as PRK,
it is a common laser vision correction procedure. PRK uses an
excimer laser to remove tissue directly from the surface of the
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
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 dociving!
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
Power, cylinder The difference (plus or minus) between the
powers measured in the two principal meridians of a lens.
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
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, 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 cylindocical component are always expressed in terms of
rear (or back) vertex power. Focimeters are designed to measure
vertex power directly.
presbyopia: A condition
occurring most commonly in people over the age of 40, where the eye
can no longer accommodate for near or "reading" vision. The
crystalline lens of the eye loses its elasticity. The individual is
no longer able to read clearly and requires reading glasses.
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
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.
Radial Keratotomy: Commonly
referred to as RK, it is a refractive corrective procedure where
radial cuts are made in the outer portions of the cornea, like
spokes of a wheel, to flatten this area.
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.
refractive surgery: A
surgical treatment that places incisions into the cornea to alter
its shape in order to treat nearsightedness, farsightedness and
astigmatisms. The use of a laser greatly improves the precision and
predictability of these procedures.
retina: The light
sensitive nerve layer in the back of the eye that receives and
transmits visual stimuli to the brain.
saccadic: Involuntary eye
movements. These rapid eye movements occur all the time, including
during laser refractive surgery and may affect accurate placement of
the laser beam.
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.
small-spot beam: At less than 1 mm in width, this type of
beam allows a LASIK specialist to perform corneal shaping in fine,
gradual, precise increments.
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
starbursts: Flares of light seen around a
lighted object that may appear like a star. This symptom is similar
to halos and may occur after surgery.
inflammation: An inflammatory reaction underneath the corneal
flap after LASIK surgery that is not due to bacteria. This condition
may result in vision loss.
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
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 childocen.
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
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
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.
undercorrection: A complication of laser
vision correction where the amount of correction is less than
desired. Some surgeons may intentionally undercorrect a particular
patient based on his or her individual situation and
vaporization: The process by
which the laser breaks the bonds of chemicals between individual
molecules with little or no damage to surrounding cells. This
process is also called photoablation.
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
visual acuity: Another phrase for visual clarity, it
refers to how clearly a person can see. Visual acuity is often
measured with a traditional eye chart.
wave: A local ripple-like irregularity
in a lens surface.
zyl: Cellulose acetate, used to make