glossary

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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 processing.

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 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.

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.

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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

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, Base

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 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.

broad-beam laser: A relatively large diameter beam (6mm - 8mm) that can be manipulated to reshape the cornea in LASIK surgery.

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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 tissue.

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 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.

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 dilation.

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.

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 astigmatism.

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.

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 fully.

epithelium: Protective layer of cells covering the cornea.

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.

excimer laser: A type of laser used in PRK or LASIK that removes tissue from the cornea.

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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 retina.

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 medical procedure.

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, 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 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.

Gaussian laser beam: A type of small-spot laser beam, its unique rounded shape leaves the corneal surface smooth.

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.


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halo: A circular flare or ring of light that may appear around a headlight or other lighted object. This symptom may occur after surgery.

hazy cornea: 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.

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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.

Intraocular Pressure: The pressure exerted on the eye by the fluids contained within the eye.

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laser radar tracker: This type of tracker is capable of tracking involuntary eye movements during surgery to ensure accurate laser beam placement.

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 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).

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.

mixed 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 retina.

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.

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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.

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OD: Latin abbreviation meaning right eye.

OU: Latin abbreviation meaning both eyes.

OS: Latin abbreviation meaning left eye.

ocular: Having to do with the eye.

ophthalmic: Pertaining to the eye.

ophthalmologist: A medical doctor who specializes in the eye and is liscenced to perform surgery on the eye. All LASIK specialists are ophthalmologists.

ophthalmology: The 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 dispenser's stock.

overcorrection: A complication of laser vision correction where the amount of correction is more than desired.

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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 addocess of the manufacturer.

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 cornea.

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 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 for kids.

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 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 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 segline.

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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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.

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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 eyes.

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.

sterile interface 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 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 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 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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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 preference.

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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.

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wave: A local ripple-like irregularity in a lens surface.

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zyl: Cellulose acetate, used to make frames.



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