Watch Us in Action Repairing Glasses in the Lab

Glossary for Eyewear Repairs and Modifications

Below are terms, in alphabetical order, often used or associated with the reparation or modification of eyeglasses or sunglasses. Feel free to scroll down the glossary to find term(s).

One of the first synthetic fibers, common material used in eyeglass frames and parts.
See Nickel Silver
A light weight metal alloy usually light in density. In eyeglasses this metal usually has to be combined with small amounts of zinc, magnesium, copper and/or silicon to enhance duribility and also usually cut out of a single block.
Anti-Reflection Coating:
Single or multi-layered application of magnesium fluoride to lens to lessen reflected light. (see our Anti-reflective coatings page for an in depth look at AR coatings)
An imaginary straight line passing through a body with respect to symmetry of the body or about which the body rotates or corresponding to a diametric dimension of the body.
Base Curve:
Dictates the surface power for a side of a lens (usually the front) into which a range of prescriptions can be surfaced generating the desired lens power. The higher the plus power the higher the base curve. The higher the minus power the flatter the base curve.
An alloy that is very flexible, corrosion and tarnish resistant with similar characteristics to titanium. Sometimes combined with copper to produce an alloy referred to as beryllium copper or beryllium bronze.
Bifocal glasses:
Spectacles with two viewing zones, one on top and one on the bottom, separated by a visible line, for seeing both near and far objects. Invented in 1784 by Benjamin Franklin.
Cable Temples:
A temple that has a flexible metal tip at the end of the shaft that comfortably wraps around the ear. Recommended for kids active adults and extreme prescriptions that produce a front heavy pair of spectacles. See riding bow for a soft flexible plastic alternative to traditional metal cable temples.
Tool to find thickness, diameter, caliber and distance between surfaces of lenses.
Carbon Fiber:
A very strong and lightweight synthetic fiber made especially by carbonizing acrylic fiber at high temperatures. Used in making eyeglass frames and parts.
An expensive metal that is usually combined to create an alloy for  thin, light, flexible and durable expensive frames.
Solid mass formed into the shape of a column/cylinder. A cylinder shaped form is ground into a lens most commonly used to help with the correction of astigmatism.
The horizontal measurement in millimeters between two lenses in a pair of glasses.
The act of moving an ophthalmic lens from its centered position.
Measurement of the transparency of a medium.
Optical unit of measurement used to represent the strength of a lens; the reciprocal of the secondary focal length in meters.
Optical unit of measurement used to represent the strength of a lens; the reciprocal of the secondary focal length in meters.
Aberration that causes straight lines to be perceived as curved.
Edged Lenses:
Lenses that have been shaped around their periphery to fit a specific frame.
End Piece:
See Frame Elbow
See Hyperopia
Figure 8 Lining:
Lining used on top portion of a semi rimless frame (rimblon frame). It is used as an interlining that fits within the groove of the lens. Called figure 8 for its profile appearance with top side of the 8 fitting within the frame and the bottom portion of the 8 fitting into the lens itself.
Flexon Titanium:
See Memory Metals
A precise place at which light rays converge or diverge when entering or exiting an optic system; To change the components of an optical system to gain clear, focused imagery.
Frame Elbow:
Joint of frame that brings together the temple and the frame itself usually concealing both ends of the eyewire..
Front Frame:
Front part of the frame consisting of the two eyepieces that are joined together by the nose bridge.
Full Frame:
An eyewear frame that consists of a complete frame around entire lens(es). Can be both metal or plastic frame.
Geometric Center:
Intersecting points of diagonals unifying opposite corners of a box and/or the vertical and horizontal lens bisectors within the boxing system, which distinguish a lens shape.
German Silver:
See Nickel Silver
Glass Lenses:
Excellent optics and high scratch-resistance, but heavy in weight and high risk of breaking and possibly hurting the eye.
Half Frame:
See Rimlon
High Index Lenses (1.60, 1.66 and 1.67):
Excellent for strong prescriptions because thinner and lighter than standard lenses; the higher the index of refraction, the thinner the lens and denser the material.
Mechanism that connects eyeglass front and temple, allowing swinging motion between them; Built of interlocking barrels.
Frames that have no hinges connecting any components of the frame together including the temples.
Farsightedness;  Defect in the eye causing rays of light from a distant source to hit the retina before coming into focus.
Circular, pigmented membrane that surrounds the eyes pupil;  Muscles that change pupil size to control the quantity of light entering the eye.
Lab Technician:
A professional that handles the production, assembly, reparation, and modification of eyeglasses and sunglasses.
Library Temples:
Also referred to as paddle temples. This temple is consistently straight with no bend on the tip (for behind the ear). Often used with readers and sunglasses.
Often used when lens is a fraction small for a frame. A lining is applied serving the purpose of a cushion/filler between the lens and the frame creating a snug fit.
Memory Metal:
Metal alloys that are usually very pliable and return to there original shapes. sometime difficult to adjust because of its memory characteristic. Some memory metal alloys include, beryllium, trilam, phosphor bronze, flexon and other titanium alloys. 
An imaginary line(s) on a sphere like surface that intersect a perpendicular axis point. Meridians may be used to help graph the anatomy of a lens, the eye or any other spherical body.
Monel Base Metal:
A metal alloy composed primarily of nickel with a portion of copper, but may contain other element like manganese, carbon, iron and silicon.. The most commonly used metal in eyeglasses and sunglasses, usually in the form of a stainless steal alloy for its anti-corrosion and durability characteristics.
Pertaining to vision with one eye.
Nearsightedness;  Problem in patients who can see things close-up, but not far away;  Light from objects being viewed does not focus on the retina, but  in front of it.
The combining of plus with minus or minus with plus lenses so as to produce a combination without power, thus determining the power of the examined lens.
Nickel Silver:
A brittle metal alloy also known as German Silver or Alpaca. This lustrous metal alloy is composed of primarily copper, balance zinc and nickel. Used for some hinges, trim, bridges, and frame elbows.
Nose Bridge:
The center piece of the frame which connects the right and left sides of the frame. Often holds nose pad arms, saddle bridge, other buffers, or are void leaving the nose bridge itself as the buffer.
Nose Pad:
A pad made of acetate, silicon, titanium metal, or other materials used as buffer between frame and the nose. Some styles include primaddona, snap-in, screw-in, saddle bridge, strap bridge amongst others.
Nose Pad Arm:
A small arm stemming from the frame used as crutch to hold nose pads. Some styles include primaddona, snap-in, screw-in, strap bridge amongst others.
Oculus Dexter, Latin for right eye.
Pertaining to the eye.
Medical doctor concentrating on the medical, optical and surgical care of the eye.
Optical Center:
Point on the optical axis where the lens does not have prism power;  An intersection point on the optical axis of a lens; Usually the thinnest point on a minus lens and the thickest point on a plus lens.
A paramedical professional who reads eyeglass prescriptions, orders lenses and sells eyeglasses and contact lenses to consumers.
Optometrist (OD):
State-licensed doctor who diagnoses and treats eye problems; Prescribes glasses, contact lenses and medicines for eye health.
A cast-molded epoxy plastic frequently used by high-end designer frame lines. This material is sensitive to heat, but has a memory that allows it to reconfigure to its original shape if overheated. Considered a very durable and anti-allergic material. Ideal for patients sensitive skin reactions.
Ocular sinister, Latin for left eye
A lens that requires a lens blank larger than 70mm, which is usually considered a standard lens blank diameter.
Progressive Addition Lens;  Lens in which the prescription strength changes continuously, providing correction for more than one seeing range. see progressive lenses.
Phosphor Bronze:
A flexible and very durable metal alloy consisting of primarily copper and very little tin and even less phosphorus.
Lens that changes color depending on the quantity of light;  More light makes the lens darker and less light makes the lens lighter Also known as transitions.
Plastic or CR-39 Lenses:
More impact resistant than glass and approximately half the weight; easier to scratch than glass; can be tinted virtually any color.
Lens with no refractive power;  The two lens surfaces are flat or uniformly meniscus in shape
Lens with a coating of parallel-oriented material that sends light waves pulsating in one direction;  Filter out reflected light, eliminating glare; Eliminate UV light
Polycarbonate Lenses:
Due to high index of refraction, these lenses are thinner, weigh less and are much more impact resistant than normal plastic lenses.
Vision problems because of old age and hardening of the eyes lens;  May include, decreasing ability to accommodate, less contrast sensitivity, requirement of more light, inability to cope with glare, etc.
Pupillary Distance (PD)
Interocular distance; horizontal linear measurement in millimeters between the centers of the pupils.
Change in direction of light when going through one medium into a different medium of varying density;  Act of deciding focal condition of eye and how to correct it
Innermost layer of the eye;  Light sensitive membrane that obtains images from the lens and delivers them to the brain via the optic nerve.
A frame that has half of the lenses exposed. These frames usually require polycarbonate lenses. Also referred to as half frames
Riding Bow:
A soft plastic temple tip that extends off the shaft of a temple and curves behind the ear. Usually applied aftermarket. Recommended for kids, active adults and extreme prescriptions that create a front heavy set of spectacles.
The front part of the frame that holds the lens(es) in place, also referred to as the eye wire.
Frameless eyeglasses and sunglasses that consist of temple ends and a nose bridge that are attached directly to the lens. The lenses are usually a polycarbonate material. this frame is also referred to as three-piece frames.
Saddle Bridge (Unifit bridge):
This bridge was derived to imitate a standard plastic frame without nosepad arms. It  distributes the weight evenly around the nose hence the name unifit. Originally derived of hard acetate the saddle bridge is now offered in soft silicone.
Spring Hinge:
A mechanism inset within the frame or temple allowing them to hyperextend. Normally located where the frame and temple come together. This feature allows for a comfortable fit as it self adjusts to the contour of the face.
Scratch resistant coating:
A strong transparent compound applied to plastic and light weight lenses in an effort to minimize scratches to the lens surface. However there is no lens material that is scratch-proof. Most lightweight lenses (high-index, polycarbonate etc.) are made of a dense materials (the higher the index the denser the material), which requires an additional coating to improve its resistance to scratches. The denser the material the harder the coat is required. One thing to keep in mind is that the harder the coating the less the lens will accept tints.
A circular object in which the surface is equidistant from the center core.
Spherical Aberration:
A defect where rays of light from various distances cannot converge to a common focus due to a defect of the spherical surface of the lens.
Single Vision (SV):
Single vision is a mono visual lens yielding a single field of vision; whether there is no prescription or a single RX prescription. The three forms of single vision lenses are plano, concave (most commonly referred to clinically as a minus prescription used to treat Myopia) and convex (most commonly referred to clinically as a plus prescription used to treat Hyperopia). There are several different materials to accommodate different needs, lifestyles and prescriptions.
Skull Temples:
Temples that slightly bend over ears and bend in following the contour of skull. It is standard on most eyeglasses manufactured.
Spring Hinge:
A mechanism inset within the frame or temple allowing the hinge to hyperextend. Normally located where the frame and temple come together. This feature allows for a comfortable fit as it self adjusts to the contour of the face.
Stainless Steal:
A steal alloy composed primarily of iron, chromium and may have very little manganese. Usually is nickel-free which gives it its anti-corrosive characteristic. Very durable and resist abrasion too.
The part of the frame that stems from the frame and rests over the ear.
Temple Shaft:
the long part of the temple between the part that tip with the hinge that connects to the frame and the temple tip that goes behind the ear.
Temple Tip:
the end of the temple that goes behind the ear.
Three Piece Frame:
See Rimless
Shades of color applied to lenses. Plastic, polycarbonate, trivex and high index lenses are dipped in dyes with temperatures reaching over 200F. These tints can be lightened by a bleaching process. Glass lenses are heat treated with oxides. Most plano sunglass  lenses are cast with colored materials, so the lens itself is consistently tinted throughout. These types of lenses do not fade. Lenses treated with a chemical dye made fade over time. Different types of tints include solid, gradient, double gradient.
Ticral Titanium:
Titanium alloy combined with copper and chrome. Lightweight, strong and nickel free, which makes it hypoallergenic. Often used on thicker metal frames.for its lightweight characteristic and it is rather inexpensive when compared to other titanium alloy
A light, strong, lustrous, corrosion-resistant transition metal with a white-silvery-metallic color. Titanium is as strong as steel, but about 43% lighter, and about 60% heavier than aluminum, but twice as strong. 
Titanium Ti-227:
A  titanium alloy that is hypoallergenic, half the weight of standard metals like stainless steal and extremely strong and anti-corrosive
Trifocal lenses are part of the multi-focal lens family most commonly used to accommodate presbyopia patients. The trifocal lens offers three fields of vision, which include distance, intermediate and near. The higher the ADD power on a RX prescription, the more notable the intermediate range is for the viewer. As the successor of the bifocal the trifocal consist of an added segment for a near field of vision like the bifocal, but also has a segment directly above to address an intermediate field of view. The trifocal lens may be an alternative to the progressive lens. Unlike the progressive lens the trifocal has a clear peripheral view with most materials, and also offers an intermediate visual range. The trifocal is offered in different segment sizes, which include 7X25, 7X28, 7X35, 8X35 and an executive style.
A metal alloy of copper, nickel and tin that is extremely pliable and light weight. Maintains its standard shape so it is difficult to adjust
Trivex was invented for the military as a polymer that is clearer and lighter than poly. The name Trivex was derived to reflect the combination of the three distinctive characteristics: excellent optics, impact resistance and lightweight nature. However, Trivex is considerably thicker than poly with a 1.53 index vs 1.59 (poly). First introduced to the public in 2003 this lens medium is an ideal material for patients that want rimless, safety, and/or sports eyewear and cannot adapt to poly and/or are looking for the clearest optics/impact resistance.
Ultraviolet protection (UV) Coating:
Besides glass, most lens materials used on eyewear have a natural composition that filters out most UV light. Added protection may be applied to achieve 100% protection from UVA and UVB light. UV coating can be applied to clear lenses, providing 100% UV coating without any color applied to the lens. Added UV protection may be added with a chemically baked on technique. However, with technological advances UV protection is most commonly applied by submerging the lens into a clear chemical agent heated to approximately 200˚ Fahrenheit for a set time, usually only a few minutes at most. (See our Ultra Violet (UV) Coatings page for more information).
The point where the optical axis of a lens coincides with the surface of the eye.
Vertex Power:
The refractive power of lens measured from its vertex to its principal focus. Vertex power is the significant factor in determining the power of a corrective lens.
Visual acuity:
Expressed as a fraction (e.g. 20/20) in which the numerator denotes the testing distance and the denominator indicates the distance at which a person with normal eyesight can resolve the letters on the chart.