Glossary of glasses parts, terms & phrases
Click a letter to alphabetically locate an optical terminology or phrase.
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | R | S | T | U | V | W | X | Z
A
Abbe
Shorthand for chromatic aberration.
Assigned to all ophthalmic lens types, this value measures the amount of visual distortion created by diverging light. Because no lens is optically perfect, it cannot focus light to a perfect point thus creating marginal defects and blur.
This deviation in optical performance varies between lens materials, resulting in slight blur for the wearer which is measured as Abbe.
Abbe values typically range from 30 to 60. The higher the value, the less aberration within the lens.
See also: Aspheric lenses | Double aspheric lenses | Refractive index | High index lenses | Low index lenses | Lens thinning | Spheric lenses | CR39 | Plano lens | Polarised lenses | Polycarbonate lenses | Trivex lenses
Absorption percentage (ABS)
Absorption percentage, often abbreviated as ABS denotes the amount of visible light absorbed by a sun lens which can be anything between 1% or 100%.
This percentage informs the five sunglasses categories which ranges from category 0 (very light) to category 4 (very dark) tinted lenses.
Visible light absorption is the opposite of visible light transmittance (VLT%) the latter of which informs the amount of visible light transmitted through a lens.
For example, 80% ABS is the same as 20% VLT.
|
Category |
0 |
1 |
2 |
3 |
4 |
|
ABS% |
0% - 10% |
10% - 20% |
20% - 43% |
43% - 85% |
85% – 92% |
|
Tint |
Very light |
Light |
Marginal |
Dark |
Very dark |
|
Sun use |
Overcast |
Low |
Moderate |
Strong |
Very strong |
|
Driving suitability |
Day & night |
Day only |
Day only |
Day only |
Never |
What are the 5 sunglasses categories?
See also: Gradient tint | Polarised lenses | Sun lens category | Tint | UV | Visible light | Visible light absorbptance | Visible light reflectance | Visible light transmittance | VLA | VLR | VLT
Acetate
Acetate glasses are made from a sheet bioplastic called cellulose acetate.
This tremendous and biodegradable material is defined as a natural polymer as its main component are the natural fibres from cotton “bolls” or wood pulp. One of the main benefits of acetate, despite its vast array of colours and patterns, is its ability to biodegrade.
See how cellulose acetate is made
See also: Block acetate | Cellon | Celluloid | Cellulose | Curing | Disperse dye | Ebonite | Galalith | Polymer | Rhodoid | Tenite | TR90 | Xyl | Zyl
ADD / Addition
Found on your prescription paper, ADD is shorthand for Addtion.
This measurement refers to the magnification section of a multifocal lens such as a bifocal, trifocal or varifocal. ADD is always measured in + , ranging from +0.75 up to around +3.00 and will always be the same for each eye.
ADD is used to correct presbyopia.
Example of ADD on prescription
See also: Prescription paper | Presbyopia | Close vision | Reading glasses | CYL | Axis | SPH
Anti-fatigue-lenses
Dual-powered corrective lenses designed to alleviate the strain of close-vision tasks such as reading and screen work.
Primarily they are single-vision distance lenses, but additionally provide relief for close-vision focus. The upper portion of the lens aids your distance or intermediate-vision, whilst the lower portion provides close-vision magnification.
Learn about anti-fatigue lenses
See also: Bifocal lenses | Single vision lenses | Varifocal glasses | HEV
AG / Anti-glare
An additional lens coating which comprises of multiple layers film structures with contrasting refractive indexes (RI.)
This alteration of RI means that light can pass through the lens more easily, rather than bouncing off it. AR makes it easier for people to see your eyes which lends itself as an upgrade for spectacle lenses. Anti-glare is also known as anti-reflective.
See also: HMC | MAR | Anti-reflective | Anti-scratch | Refractive index
AR / Anti-reflective
The same as anti-glare.
This coating lets more light pass through a lens instead of being reflected off the lens surface. This coating is particularly popular for spectacles to reduce glare on the lens which makes it easier for people to see your eyes.
*Anti reflective coating can be applied to the back-side of sunglasses lenses to reduce “bounce back.”
See also: Bounce back | HMC | MAR | Anti-reflective | Anti-glare | Anti-scratch | Oleophobic | Hydrophobic | Refractive index
Anti-Scratch
A hardy lens coating to minimise scuff and micro scratches on the surface of your lenses. This is integrated with MAR and comes at no extra cost with our glasses frames.
See also: HMC | MAR | Anti-reflective | Anti-glare | Oleophobic | Hydrophobic | Refractive index
Aspheric lenses
A lens with varying curvatures across it's front surface profile.
These curvatures make a lens thinner, flatter and lighter weight than a spheric equivalent. Not to be confused with high-index lenses which denotes the refractive index of a lens.
Spherical vs aspherical lenses
See also: Abbe | Double aspheric lenses | Low index lenses | Refractive index | Spheric lenses | High index lenses | HMC | MAR | Anti-reflective | Anti-glare | Oleophobic | Hydrophobic
Astigmatism
An uneven curvature in the cornea or sometimes in the lens of the eye. These irregularities are distinguished by an asymmetry in the cornea or the crystalline lens. As opposed to being spherically symmetrical, one side is more curved than the other.
See also: CYL | Prism | Myopia | Presbyopia | Axis | ADD | SPH | Prescription paper
Average PD
This is a singular measurement of the distance between both of your pupils and can be averaged based on your gender.
- Average male PD = 64mm
- Average female PD = 62mm
How to measure your pupillary distance
See also: PD | Dual PD | Single PD | PD ruler | Ocular centre | Centration
Axis
Written on your prescription paper, Axis is written as a number between 1 and 180. This refers to the angle of any cylindrical power (CYL) required to correct your astigmatism.
See Axis on an eye prescription
See also: ADD | CYL | SPH | Astigmatism | Prescription paper
B
Baleen glasses
Another term for whalebone.
Baleen is completely outdated and is unavailable new. A by-product of whaling, this natural material was used to make glasses frames between the 17th and 19th century. It is very flexible when heated and remains springy when cold, a viable material at the time to secure optical lenses.
See also: Acetate | Bone glasses | Ebonite glasses | Gold glasses | Ivory glasses | Leather glasses | Tortoise shell glasses | Shagreen glasses | Wooden glasses
Base curve
Also called BC, BCR or BCOR (back central optic radius.) Measured with a lens clock, base is the curvature of the back of a lens. It is measured across three points of an arc, two at the side and one in the middle of the lens.
See also: Frame curving | Lens diameter
Bevel
The double angle cut onto the edges of glasses lenses, usually at 120° as per BS lens standard. Sometimes lens bevels can vary anywhere between 80° to 180° which may hinder glazing for lens technicians.
See also: Lens groove | Glazing | Full rim | Half rim | Rimless | Supra
Bifocal lenses
This lens type contains two separate lens segments.
An upper, main portion of the lens is for distance/intermediate viewing and a small segment for close reading. The reading segment is always a positive dioptre + and is a visible segment within the lens.
See also: D-Seg lens | Round-seg-lens | Franklin lens | ADD | Anti-fatigue lenses | Varifocal glasses | Trifocal lenses
Blade temple
A straight temple with no drop end to hook behind your ear.
Otherwise called a “paddle temple” this design makes it completely straight. (Some designs may taper in width but in order to be a blade/paddle temple, it must not have a drop.)
See also: Paddle temple | Temple | Tip | Drop end | Hockey end | Blade temple | Curl sides | Wire core
Block acetate
This terms describes the process of making large "blocks" of cellulose acetate.
The cellulose acetate mixture is poured into deep block-moulds which is left to cure (set.) Once fully cured, the large acetate blocks are then hydraulically pushed against a cutting knife which skims the acetate into 6/8mm thick sheets.
See how cellulose acetate is made
See also: Acetate | Cellon | Celluloid | Curing | Disperse dye | Ebonite | Galalith | Polymer | Rhodoid | Tenite | TR90 | Xyl | Zyl
Bone glasses
With similar properties to wood, albeit available in smaller sections, glasses made from animal bone were common right up to the 19th century. The bone was usually taken from the shin or skull of cattle such as sheep or cow.
See also: Acetate | Baleen glasses | Ebonite glasses | Gold glasses | Ivory glasses | Leather glasses | Tortoise shell glasses | Shagreen glasses | Wooden glasses
Bounce back
This is when sunlight enters from behind or from above a lens which can lead to the light being reflected backward into your eyes.
Bounce back is more noticeable with sunglasses frames and is preventable with an anti-glare/anti-reflective coating only on the rear side of the lens.
See also: HMC | MAR | Anti-reflective | Anti-glare | Anti-scratch | Oleophobic | Hydrophobic | Refractive index
Bridge
The central section of a glasses frame which arcs over your nose. Sometimes called a nose-bridge.
There are various types and styles of bridge which vary depending on the material used to make the frame. Traditionally, the bridge would have been part of the same piece of material that made the entire frame front.
In later technologies, such as rimless frames, the bridge could be use to affix two lenses together through fine drill-holes.
See also: Bridge width | Frame dimensions | Nose bridge | Keyhole bridge | Regular bridge | Bridge bumping | Bridge apical radius | Frame front
Bridge apical radius
This measurement is taken from the uppermost region inside the nose bridge where your frame makes room for your nose. The diameter of this aperture is measured and divided in half.
See also: Bridge | Keyhole bridge | Regular bridge | Frame front
Bridge bumping
The process of heating and indenting the bridge in an acetate frame front.
The frame front is heated, on its own inside a an oven to make the acetate bendy and malleable. It is then secured in a specific jig-holder to align it in place for bumping. Under pneumatic pressure, a brass wedge is deployed downwards onto the heated frame.
This controlled impact creates the bump on the bridge section, perfect for facial comfort as the frame would otherwise rub/conflict with your upper-nose.
See also: Frame heating | Bridge | Frame curving | Keyhole bridge | Regular bridge | Frame front
Bridge width
Usually pad printed or laser etched onto the inside of the temple.
This measurement is written in as the second in the series of digits that indicate the dimensions of a glasses frame. (Eg: 52 [] 18 135.) Bridge widths vary between children’s, women’s and men’s frames, usually 16/24mm wide.
Learn about glasses frame dimensions
See also: Bridge | DBL | Frame dimensions | Lens diameter | Temple length | Pad printing | Laser etching
C
Cataracts
A condition that describes the cloudiness in the eye lens, common for elderly people of around the age of 80. There are three types of cataracts which are listed as nuclear, cortical or posterior.
CE mark
CE stands for Conformité Européenne, which is French for "European Conformity".
Spectacles and sunglasses which are compliant with EU regulations must bear the CE mark. This emblem is usually located on the inner surface of the temple or frame, marked via pad printing or laser etching.
On sunglasses frames, the CE mark signifies that the lenses are capable of UV (ultraviolet) protection up to 380nm (nanometres). Whilst the CE mark denotes European standards conformity, it's best that sunglasses are actually rated as UV40 or UV400 which provides protection up to 400nm.
What does CE mean on sunglasses?
See also: Frame dimensions | Laser etching | Pad printing | UV400
Cellulose
The most common organic compound on planet earth.
It is an integral component, found within the structures of many types of fauna. For the production of cellulose acetate for spectacle making, cotton and wood pulp are favourable sources of cellulose due to their inherently high percentages.
Since it's use in sheet polymer production, cellulose acetate has been replicated and trade marked under various names as seen below.
See also: Acetate | Block acetate | Cellon | Celluloid | Curing | Disperse dye | Ebonite | Galalith | Polymer | Rhodoid | Tenite | TR90 | Xyl | Zyl
Cellulose acetate
High quality, full-rim glasses frames are either handcut or CNC machined from a sheet bio-plastic called cellulose acetate.
This tremendously variable and biodegradable material is defined as a natural polymer as its main component are the natural fibres from cotton “bolls” or wood pulp.
See how cellulose acetate is made
See also: Acetate | Block acetate | Cellon | Celluloid | Curing | Disperse dye | Ebonite | Polymer | Rhodoid | Tenite | TR90 | Xyl | Zyl
Cellon
The German trade-name for cellulose acetate, used by "Deutsche Celluloid Fabrik, Eilenburg." It's rudimentary properties consist of purified cellulose and acetic acid which is then coloured using dispersing dyes.
See how cellulose acetate is made
See also: Acetate | Block acetate | Celluloid | Cellulose | Curing | Disperse dye | Polymer | Rhodoid | Tenite | Xyl | Zyl
Centration
A combination or horizontal and vertical measurements to ensure the proper alignment of your pupil with the optical centre of your lenses.
Horizontal centration is achieved via pupillary distance measurements which can be either single or dual, depending on your use of glasses.
Vertical centration is achieved by measuring your ocular centre heights(OC heights.) These is the distance (in mm) from the bottom of your lenses to the centre of each of your pupils. Your OC heights change from frame to frame as it depends on how the glasses fit your head.
How to measure your ocular centre heights
How to measure your pupillary distance
See also: Ocular centre | Ocular height | PD | Dual PD | Single PD | Average PD | PD ruler
Celluloid
A nitro-cellulose substitute for Ivory, first conceived in Birmingham, UK by Alexander Parkes. Initially, it was called Parkesine, then Xylonite before finally being officially registered as Celluloid in 1870. Celluloid was briefly used in the production of spectacle frames but became obsolete due to it's highly flammability properties.
See also: Acetate | Block acetate | Cellon | Cellulose | Curing | Disperse dye | Galalith | Polymer | Rhodoid | Tenite | CNC Machining | Xyl | Zyl
Charnier
Part of a glasses hinge, charniers are the threaded metal loops which protrude from the base-plate of the glasses hinge.
Also called chenier, tenons or barrels, the charnier rings interlock with one another and are secured with a threaded dowel screw. Hinges vary in charnier/tenon counts ranging from a three-tenon, five-tenon and occasionally a seven-tenon.
See also: Tenons | Hinge | Hidden hinge | Half joint | Joint | Spring hinge | Dowel screw | Thread seeking screw
Ciliary muscles
The muscle group in your eye which contracts and relaxes the zonule fibres surrounding your eye-lens.
Depending on the amount of contraction, the ciliary muscles squeeze and alter the shape of your lens which lets you change your distance of focus.
Over time, these muscles begin to weaken slightly which can hinder your close vision. This is perfectly common at middle age as part of the common condition called presbyopia, which can be corrected with the use of ADD in your prescription lenses.
See also: ADD | Reading glasses | Presbyopia | Pupil | Iris | Cornea | Zonules
Close vision
Close vision is determined by visual tasks that are within 35cm from your eyes.
If you struggle with close vision, you may be hyperopic or have the age-related presbyopia. This will be evident from your prescription if you have a positive (+) value in your Sphere boxes for each of your eyes.
Reading glasses are specifically designed to help your close reading which is why they aren’t useful for intermediate or distance tasks such as computer work or driving.
How to understand your prescription
See also: Intermediate vision | Distance vision | Presbyopia | Myopia | Hyperopia
Cornea
The front part of your eye which covers your pupil, iris and anterior chamber.
See also: Pupil | Iris | Ciliary muscles | Zonules
Crown glass
A type of optical glass to make ophthalmic lenses.
It is free from lead and iron and has a low refractive index of 1.523. Crown glass has the toughest of lens surfaces however it has become largely outdated by synthetic plastic lens materials such as CR39, polycarbonate or Trivex.
See also: Aspheric lenses | Double aspheric lenses | Lens | CR39 | Plano lens | Polarised lenses | Polycarbonate lenses | Refractive Index | Trivex lenses
Cross head screw
A threaded screw used to secure the hinges/joints of a glasses frame together.
Cross head screws are characterised by their a dual intersection recess across the top of the head of the screw. This is where a small “Philips” screwdriver is located and turned to tighten the hinge mechanism.
Glasses screws locate into the threaded charniers of a hinge.
See example of cross head screws
See also: Dowel screw | Thread seeking screw | Hinge | Joint | Charnier
CR39
A synthetic thermosetting plastic used for making spectacle lenses developed in 1949 by Columbia Resins. It was the 39th iteration of their formula which paved the name for CR39.
See also: Demo lenses | Polycarbonate lenses | Trivex lenses | Crown glass | Polarised lenses
Curing
This chemical term describes the hardening of a polymer. In the production of cellulose acetate, the mixture is poured into blocks and squeezed under pressure whilst it is left to become solidified.
Other materials such as resins, paints or types of adhesive also use the term cure. For example, Galalith; a semi-synthetic polymer made using cow's milk.
See how cellulose acetate is made
See also: Acetate | Block acetate | Cellulose acetate | | Disperse dye | Ebonite | Galalith
Curl sides
A thin wire temple which is curled at the end to hook round your ear.
Most commonly, this type of temple-end is sprung in order to wrap behind your ear to provide a secure and snug fit. Curl sides are known to prevent frame-slippage, which makes them popular for certain occupations such as tailoring where large amounts of time are spent looking downward over a cutting table.
See also: Paddle temple | Temple | Tip | Drop end | Hockey end | Blade temple | Wire core
CYL / Cylinder
Found on your prescription details, these digits indicate the required amount of lens power to correct the astigmatism in your eye.
These digits can be written as a positive or a negative figure, depending if you have near or farsighted astigmatism. If your prescription states no CYL digits, you do not have astigmatism.
See also: Axis | SPH | ADD | Prism | Prescription paper
D
DBL
This is an acronym for Distance Between Lenses which is measured from the innermost edge of each neighbouring lens. This distance in taken where the lenses are closest and is subtracted by 1.5mm to account for the lens groove.
See also: Lens groove | Lens diameter | Bridge width | Frame dimensions
Deco rivets
A decorative piece of hardware designed to mimic the use of rivets in a frame front.
Deco rivets are added to frames that use a "hidden hinge" which are instead held in via heat insertion. These decorative inserts yield the impression of a traditional hinge but provide no actual function.
See also: Hidden hinge | Hinge | Hinge grave | Joint | Rivet | Riveting | Charnier
Demo lenses
For demonstrative purposes in retail or home-trial scenarios, spectacle frames are fitted with what are called demo lenses.
Demo lenses are fitted to simulate corrective lenses, simply to give you an idea of what the frame will look like in a more realistic aesthetic.
Despite providing no corrective power, demo lenses are not the same as plano lenses. For display purposes only, demo lenses are cheaply made from thin acrylic and don’t provide any UV or blue light protection for your eyes.
The difference between demo & plano lenses
See also: Lens | Glass lenses | Crown glass | CR39 lenses | Polarised lenses | Polycarbonate lenses | Refractive index | Trivex lenses | Plano lens
Dioptres
A measurement that refers to the optical power of lens. On your prescription, dioptre can be abbreviated as “D.”
See also: ADD | Axis | CYL | SPH | Prism | Prescription paper
Disperse dye
The powdered dyes used to give cellulose acetate its colour. To thoroughly incorporate them, the dyes are mixed with the neutral acetate compound and repeatedly rolled through motorised metal rollers.
See how cellulose acetate is made
See also: Acetate | Block acetate | Cellulose | Cellon | Celluloid | Curing | Polymer | Rhodoid | Tenite | Xyl | Zyl
Distance vision
As opposed to close or intermediate vision, distance vision refers to tasks beyond arm’s length such as watching television, driving or playing sport.
See also: Close vision | Distance vision | Presbyopia | Myopia | Hyperopia
Double aspheric lenses
A lens with varying curvatures across it's front and rear surfaces.
These curvatures make a lens thinner, flatter and lighter weight than a spheric and/or a single aspheric equivalent. Not to be confused with high-index lenses which denotes the refractive index of a lens.
Double aspherical lenses explained
See also: Abbe | Aspheric lenses | Low index lenses | Refractive index | Spheric lenses | High index lenses | HMC | MAR | Anti-reflective | Anti-glare | Oleophobic | Hydrophobic
Double rivet hinge
A metal hinge, also called a joint, which is fastened using two rivets through the frame front and two through the temple. This style of hinge is very traditional and can be orientated so the rivets can be vertical or horizontal.
See also: Triple rivet hinge | Hinge | Joint | Spring hinge | Hidden hinge | Hinge grave
Dowel screw
A threaded screw used to secure the hinges/joints of a glasses frame together.
Dowel screws are characterised by the linear intersecting recess across the top of the head of the screw. This is where a flat headed screwdriver is located and turned to tighten the hinge mechanism.
The screw itself locates into the threaded charnier of the hinge.
See also: Cross head screw | Thread seeking screw | Hinge | Joint | Charnier
Drop end
This is the angled portion of a temple which “drops” downward behind the ear, usually at an angle of 45 degrees. The drop end on a temple can also be called a “hockey end” as it similarly resembles a field hockey stick.
See example of a drop end temple
See also: Hockey end | Paddle temple | Temple | Tip | Blade temple | Curl sides | Wire core
D-Seg lens
A bifocal glasses lens with a D shaped segment in the bottom region of the lens
Learn more about bifocal glasses
See also: Round-Seg lens | Franklin lens | Bifocal lenses
Dual PD
This refers to the distance from the centre of your nose to each centre of your pupils.
Used for more complex prescriptions such as progressive lenses, both of these measurements are in mm and are noted seperatley for each eye. A relatively accurate PD measurement is required to align the optical centre of each lens with your pupil.
See also: PD | Dual PD | Average PD | Optical centre | Ocular centre | Centration
How to measure your pupillary distance
E
Ear hooks
An attachable “hook” which can be added to your temples to prevent your frame from slipping down your nose. These are usually an aftermarket addition, usually made from injected plastic and cost very little money.
See also: Temple | Curl sides | Hockey end
Ebonite
A slow-vulcanised natural rubber that resembles Ebony hardwood. This semi-synthetic polymer comprises of latex milk-sap from ethically harvested Sri Lankan caoutchouc-trees, mixed with high levels of sulphur.
Characteristically, Ebonite takes several days to vulcanise and has the appearance of ebony wood, hence it's most common trade name; Ebonite. Also sometimes called Vulcanite.
Historically, Ebonite was used to make bowling balls until the late 20th century as it could be easily moulded, machined and polished to a high lustre.
*According to our supplier (2020), Banton Frameworks are the only company to have used Ebonite for the production of eyewear.
See also: Acetate | Bone glasses | Galalith | Gold glasses | Ivory glasses | Leather glasses | Tortoise shell glasses | TR90 | Shagreen glasses | Wooden glasses
Endpiece
The outermost edges of your glasses frame where the temples connect to the frame front. The endpieces make room at the upper outside edges of each lens to make room for the hinges.
See also: Frame front | Bridge | Temple | Hinge | Screw | Lens | Lens groove | Half rim | Full rim
F
Frame front
The main part of the glasses frame which holds the lenses.
There are three main types of frame front which are either full rim, half rim or rimless. Full rim or half rim frame fronts can made from various materials such as acetate, wood or horn.
Rimless frame fronts are screwed together via a metal bridge between each of the lenses and have no outer-rim, hence the term rimless.
Example of a glasses frame front
See also: Full rim | Half rim | Rimless | Bridge | Lens groove | Bevel | Glazing | Supra
Frame curving
The process of heating and curving the acetate frame front to incorporate the desired base curve for the lenses.
See also: Bridge bumping | CNC machining | Tumble polishing | Riveting | Staking | Hand polishing | Ultrasonic cleaning
Frame dimensions
A series of digits which are located on the inner surface of the frame, usually on the temple. These numbers are listed a particular order which refer to the lens diameter, bridge width and temple length respectively. Eg: 52 [] 18 135. These dimensions are created via laser etching or pad printing.
Learn about glasses frame dimensions
See also: Pad printing | Laser etching | Lens diameter | Bridge width | Temple length
Frame heating
Heating can be applied spectacle frame for various purposes, both during and/or after it's manufacture.
For glazing: Frame fronts made from acetate or horn can be heated using a fan powered blow-heater. Similar to a hairdryer, the frame front is softened by the hot air which makes it easier to fit lenses into the lens groove. This is usually carried out by a lens technician or optometrist.
For adjustments: Fronts or temples can be heated to allow them to be adjusted. This can be done several times to get the perfect fit.
For manufacture: Frame fronts and temples separately undertake various stages of heating during their stages of manufacture.
Fronts are heated in an enclosed oven to the point of deformation. This makes them suitably malleable for bridge-bumping or to impart the desired base curve.
Temples can be heated, nearly to the point of deformation, in order to insert their reinforcing wire cores.
Temples can also be heated to introduce the drop-end and head curvature. Both of these curves are applied to make them more comfortable to wear.
See also: Pad printing | Laser etching | Lens diameter | Bridge width | Temple length | Wire core
How wire cores are inserted into hot acetate
Franklin lens
Invented by Benjamin Franklin in the 1780’s, the founding father took two differently powered glasses lenses and cut them in half.
He then joined the two halves together to form what became known as one of the first types of bifocal lens. The upper lens was for distance viewing and the lower was for close reading.
The original Franklin lenses were cemented together at the join but modern versions are now single piece with an intersecting and visible line across the lens.
Learn more about bifocal glasses
See also: D-Seg lens | Round-Seg lens | Bifocal lenses
Full rim
A frame front which fully surround the edges of each lens, usually made from cellulose acetate.
See also: Half rim | Rimless | Supra | Glazing
G
Galalith
A semi-synthetic polymer invented in 1870. This rudimental plastic is made from casein, the main protein component of cow's milk and is mixed with formaline and dyes to resemble horn or marble.
Made and distributed under many trade names around the world, Galalith was used to manufacture all manner of products. For example combs, hair-brushes, buttons, buckles, cutlery handles, knitting needles, guitar plectrums and optical frames.
See also: Block acetate | Cellon | Celluloid | Cellulose | Curing | Ebonite | Polymer | Rhodoid | Tenite | TR90 | Xyl | Zyl
Glass lenses
The first versions of spectacle frames were fitted with lenses made of glass.
Prior to the discovery and use of plastics, glass was the only material that could be used to see through and provide visual correction.
Glass lenses provide the truest ocular performance compared to any other lens material with a refractive index ranging from 1.6 to 1.9.
See also: Lens | Crown glass | CR39 lenses | Demo lenses | Plano lens | Polarised lenses | Polycarbonate lenses | Refractive index | Trivex lenses
Glaucoma
A threatening but preventable condition which involves the build-up of pressure of the synovial fluid in the eye. If unchecked, this can lead to damage of the optic nerve and pose the threat of permanent loss of vision in one or both of the eyes.
See also: Cataracts
Glazing
The process of fitting prescription, plano or demo to a spectacle or sunglasses frame.
Depending on the material and construction of the frame, glazing is carried out using various methods. For acetate frames, the frame front is usually heated to make the acetate more malleable which makes it easier to push the lenses in.
See also: Frame heating | Full rim | Rimless | Lens groove | Bevel | Supra
Gold glasses
Over time, glasses frames have been regularly cited as being gold in colour.
Whether they were actually made from gold is uncertain as the precious metal itself is too soft and heavy to be remotely practical. Gold plating is far more probable and is obviously a more modern technique.
See also: Acetate | Bone glasses | Baleen glasses | Ebonite glasses | Ivory glasses | Leather glasses | Tortoise shell glasses | Shagreen glasses | Wooden glasses
Gradient lens tint
A sunglasses lens where the tint is darkest at the top of the lens and lightest at the bottom.
This is to bock sunlight from above where it’s the most intense without having a completley darkened lens. This allows people to still see your eyes which gives you the best of both.
How tints affect visible light transmittance
See also: Absorbption percentage | Tint | VLT | Sun lens category | Polarised lenses | UV | Visible light
H
Half joint
One half of a glasses hinge.
Each half joint intersects with one another via the tenons which create the the joint between the frame front and the temple. Each frame has four half joints which connects with each of the left and the right temple.
Half joints may be called "frame half joint" or "temple half joint" to indicate which part of the hinge is being described.
See also: Joint | Tenons | Charnier | Frame front | Temple | Hidden hinge | Spring hinge | Hinge grave | Rivet
Half rim
A frame front which is made from a solid material like acetate which holds the upper half of each lens. The lower part of the lenses are left exposed, usually secured using a supra chord.
See also: Supra | Full rim | Rimless | Lens groove | Bevel | Glazing
Hand polishing
Also known as wheel, rag or mop polishing.
This is the multi-stage process of polishing acetate frame fronts and temples. It is carried out using a motorised rotating mop and polishing compounds.
The frame/temples are skilfully polished against the mop in order smooth the surfaces of the acetate to achieve a high finish. Increasingly fine grades of polishing compound and mops are used to bring the acetate to a glossy lustre.
Other surface styles can be achieved via textured mops which can yield a matte or brushed surface finish.
See also: Tumble polishing | CNC machining | Ultrasonic cleaning
Hard-case
The best place to store your glasses when you’re not wearing them. Each Banton Frameworks frame is accompanied by a bespoke BFW hard-case and lens cloth to keep your glasses safe and secure.
See also: Lens cloth
HEV
Initialised for High-Energy-Visible light, also called blue light. This particular frequency of light is part of the electromagnetic spectrum at 400/450 nano metres. It is also emitted from digital screens such as your computer or phone screen.
More about blue light blocking lenses
Hidden hinge
Also called a “sunk hinge.”
This type of hinge hides its method of attachment to the frame front as it's devoid fasteners such as rivets.
Instead, a hidden hinge is inserted into a pre-machined grave on the rear-side of an acetate frame front via heat or ultrasonic friction. This process melts the acetate around it and secures it in place.
Hidden hinges are rarely repairable but require less parts/skill to insert. They are common amongst low cost or fashion frames to avoid the use of rivets.
Glasses frames with hidden hinges may adorn decorative rivets to mimic the traditional construction aesthetic of real rivets.
See also: Deco rivets | Hinge | Hinge grave | Spring hinge | Staking | Riveting | CNC machining
High index lenses
An optical lens with a refractive index higher than 1.5.
This means the lens is more efficient at bending light, therefore can be thinner and lighter, especially at the edges. This prevents the lens-edge from "spilling" out from the edges of the frame, beyond the lens groove.
If you require a strong negative prescription to correct myopia, high index lenses are preferable to reduce the weight and thickness of your lenses.
See also: Abbe | Aspheric lenses | Double aspheric lenses | Spheric lenses | Myopia | Low index lenses | Lens thinning | Refractive index | Lens groove
Hinge
This is the moving part with conjoins the frame front and the temple.
Hinges are most commonly made from steel, brass or nickel alloy and secured via rivets, heat or friction. Low cost eyewear frames have been known to use plastic hinges which are generally injection moulded using synthetic polymers.
See also: Charnier | Tenons | Half joint | Hidden hinge | Hinge grave | Spring hinge | Staking | Riveting | Screw | Dowel screw | Cross head screw | Thread seeking screw
Hinge grave
The recess in which a hinge locates, either in the frame front or in the temple.
Hinge graves are predominant in full rim glasses frames made from acetate. The graves help to secure hinges in place and make the hinge flush with the top surface of the frame. Within the hinge grave are also the rivet holes where the rivets locate through the frame front.
See also: Hinge | Rivet | Rivet hole | Hidden hinge | Spring hinge | Staking | Riveting
HMC
An abbreviation for Hard Multi Coat. A multi-layer lens coating which contains anti-reflective and anti-scratch.
See also: MAR | Anti-reflective | Anti-glare | Anti-scratch | Oleophobic | Hydrophobic | Refractive index
Hockey end
This is the end-portion of a temple which drops downward behind your ear. Otherwise called a "drop end" this part of the temple prevents the glasses frame from sliding off your face.
Example of a hockey end temple
See also: Curl sides | Temple | Tip | Drop end | Blade temple | Paddle temple | Wire core
Home try-on
For 7 days, you can borrow your glasses for free to try them at home.
Your entire payment is delayed by 7 days to allow you plenty of time to decide if you'd like to return them to us for lens fitting or for a refund. This feature is powered by the financial service company, "Klarna."
In partnership with Klarna, we've implemented this concept to bypass the uncertainty of buying your glasses or sunglasses online. Rather than traditional brick and mortar retail, you can try your glasses at home instead of in an optician or fashion store.
See also: Virtual mirror | Klarna
Horn glasses
Since the conception of the first spectacle frames, horn was a go-to material for making the first glasses frames.
Primarily, ox-horn would have been used, but more recent frame-iterations are made using buffalo-horn. Today, less and less frames are made using horn and generally has a higher perceived value than acetate.
See also: Acetate | Bone glasses | Baleen glasses | Ebonite glasses | Gold glasses | Ivory glasses | Leather glasses | Tortoise shell glasses | Shagreen glasses | Wooden glasses
Hydrophobic
A very thin lens coating made of titanium dioxide which repels water.
See also: HMC | MAR | Anti-reflective | Anti-glare | Anti-scratch | Oleophobic | Refractive index
Hyperopia
The optical term used to describe long-sightedness. This condition means you can see things far away but struggle with close distance focus.
See also: Myopia | Presbyopia | Close vision | Intermediate vision | Distance vision
Hypoallergenic
A material with reduced likelihood of causing an allergic reaction.
In the context of eyewear, glasses made from cellulose acetate are known to be hypoallergenic. This attribute is helpful for glasses wearer who suffer with sensitive skin. Glasses made from metal parts such as nickel may cause allergic reaction which is why acetate can be a preferable material.
See also: Acetate | Nickel | Cellulose
I
Interpupillary distance
This is the total distance between the centres of your eyes and is measured in mm.
See also: Pupillary distance | Dual PD | Single PD | Average PD | PD ruler | Ocular centre | Centration
How to measure your interpupillary distance
Intermediate vision
Refers to visual tasks that occur about an arm length away at approximately 90cm or so. A good example of this is using a computer which is beyond the distance of close vision.
How office varifocal lenses help intermediate vision
See also: Close vision | Distance vision | Presbyopia | Myopia | Hyperopia
Iris
The circular diaphragm in your eye/s which controls the amount of light that enters through your pupil. Via pigmentation your iris determines the colour of your eyes.
See also: Cornea | Ciliary muscles | Pupil | Retina | Zonules
Ivory glasses
Soon to become completely illegal to buy or sell in the UK, ivory glasses frames are very much a taboo item.
Historically, ivory frames were made during the 15th to 19th century and were similarly worked like horn or bone, usually carved and sculpted with a sharp cutting tool.
Typically, the tusks of African or Indian elephants were used, However the teeth of the hippopotamus, walrus, narwhal, sperm whale, and some types of wild boar were also used.
See also: Acetate | Bone glasses | Baleen glasses | Ebonite glasses | Gold glasses | Leather glasses | Tortoise shell glasses | Shagreen glasses | Wooden glasses
J
Joint
Another term used for a hinge. Joints are almost always made from metal and can vary in size, tenon-count and fixing method.
Example of different glasses joints
See also: Half joint | Charnier | Tenons | Hinge | Hidden hinge | Hinge grave | Spring hinge | Deco rivets | Riveting
K
Keyhole bridge
The aperture where your nose locates.
This bridge-type resembles an old fashioned key hole. This detail is associate with older, more classic full-rim acetate frame fronts.
See also: Bridge | Regular bridge | Bridge bumping | Full rim | Half rim | Frame front
Klarna
Klarna is a financial service system that allows you to delay your purchase payment by 7 entire days.
At the Banton Frameworks checkout, you can select "Pay Later With Klarna" which allows you try your glasses at home first, before paying for them. Cleverly, you don't require an account prior to using it to delay your payment.
See also: Home try on | Virtual mirror
L
Laser etching
A detailed and computer-controlled method of permanently marking the part of glasses frames.
Etching can be applied to the surfaces of the frame front, temple and occasionally the lens for branding branding purposes.
Predominantly, laser etching is used to mark details such as frame model, manufacturer and frame dimensions. Etches can be left either blank or filled with coloured ink to increase legibility.
Learn about glasses frame markings
See also: Pad printing | Frame dimensions | Bridge width | Lens diameter | Temple length
Leather glasses
Since the invention of spectacles, leather has been a predominant material to make glasses frames from.
Whilst still soft, thick sections of cow or goat leather would be cut into shape. They would then be boiled in hot water to make them tough and stiff, thus able to retain lenses.
See also: Acetate | Bone glasses | Baleen glasses | Ebonite glasses | Gold glasses | Ivory glasses | Tortoise shell glasses | Shagreen glasses | Wooden glasses
Lens
A transmissive solid used to focus or disperse light via refraction.
Early examples of spectacle lenses were made from glass as this was the only feasible material which could be used to correct vision. The name lens derived from the Latin name lēns for lentil due to the biconvex shape of glass lenses.
See also: Abbe | Aspheric lenses | Double aspheric lenses | Glass lenses | Crown glass | CR39 lenses | Demo lenses | Plano lens | Polarised lenses | Polycarbonate lenses | Refractive Index | Spheric lenses | Trivex lenses
Lens cloth
A small square lens cloth made from a micro-fibre material used to clean your lenses. Best stored inside your glasses hard-case.
See also: Hard case
Lens diameter
Usually pad printed or laser etched onto the inside surface of the temple. This measurement is written in as the first in the series of digits that indicate the dimensions of a glasses frame. Eg: 52 [] 18 135.
Learn about glasses frame dimensions
See also: Bridge width | Frame dimensions | Temple length | Pad printing | Laser etching
Lens groove
The angled recess within the rim of an acetate glasses frame which receives and secures the lens. The lens groove is precision machined using tool which has a cutting angle of 120° as per BS lens standards. The depth of the lens groove is usually 1.5mm.
To fit a lens into the lens groove, acetate or horn glasses frames fronts are heated using a fan powered blow-heater.
See also: Glazing | Bevel | Frame heating | CNC Machining
Lens thinning
The option to reduce the weight and thickness of a prescription lens.
This reduction is advisable for strong prescriptions more than +/-4.00 SPH. This prevents having chunky, cumbersome lenses and generally improves the look of your glasses frame.
Previously, high-strength lenses without lens thinning would appear overly thick, hence the term "milk bottle glasses."
Suggestions for ordering the correct lens thinning option
- Thinned: SPH +/-4.00-6.75 CYL max +/- 2.00
- Super Thin: SPH +/-7.00-9.00 &/or CYL max +/- 2.00
- Ultra thin: SPH +/-7.00-9.00 &/or CYL +/-2.25-6.00
See also: Abbe | High index lenses | Low index lenses | Refractive index | Aspheric lenses | Double aspheric lenses | Spheric lenses | Prescription paper | SPH | CYL
Let back
This is the angle between the frame front and the temple.
On acetate frame fronts, the let back can be adjusted by filing the area where the temple meets the frame. This makes the head-width wider and yields a looser fit on the sides of your head.
See also: Mitre | Hinge | Joint | Temple | Frame front | Pantoscopic tilt
Lornette
An old fashioned glasses frame which is handheld, rather than worn on the face.
Conceived in 1770, lorgnettes have no temples and would often have a handle where the wearer could hold it to their face. In some designs, the handle could be folded way like a shaving razor.
See also: Monocle | Temple | Curl sides
Low index lenses
An optical lens with a refractive index of 1.50
Low index lenses are generally thicker as they are less efficient at bending light. This doesn't make them bad quality, it simple means they're thicker than an equivalent, higher index lens to create the same corrective power.
Low index lenses are suitable for low/mild strength of prescriptions. This reduces unnecessary cost for a lens that doesn't require lens thinning.
See also: Abbe | High index lenses | Lens thinning | Refractive index | Aspheric lenses | Double aspheric lenses | Spheric lenses
M
Machining / CNC Machining
A computer controlled process also known as CNC machining. This involves the cutting of sheet acetate using various cutting bits at various speeds to make the glasses frame front and temples.
See also: Tumble polishing | Hand polishing | Frame curving | Bridge bumping | Riveting | Ultrasonic cleaning
MAR
An acronym for Multi-layered Anti-Reflective.
MAR is a term that refers to the multiple layers within the anti-reflective lens coating. MAR is used to improve the quality and efficiency of a glasses lens by reducing reflected light. Instead it lets more light pass through the lens which improves visual acuity.
See also: HMC | Anti-reflective | Anti-glare | Anti-scratch | Oleophobic | Hydrophobic | Refractive index
Mitre
Where the glasses frame front and temple meet one another, usually at an average angle of 6° known as “let-back.”
See also: Let back
Monocle
A singular corrective lens secured within an entirely circular rim, usually made from wire or acetate. They became popular amongst 19th century gentry and were worn as an optical accessory via a chain or string, much like a pocket watch.
See also: Lorgnette
Myopia
This is the optical term for near-sightedness which means you can see close objects clearly but need correction for distance viewing.
You'll know if you're myopic if you're Sphere value on your prescription shows a negative value (-).
See also: Hyperopia | Presbyopia | Sphere
N
Nickel
A silvery white metal with a slightly golden tinge.
Used in minor parts of glasses frames such as the hinges, rivets or push-in nose pads. Relatively cheap and easy to produce parts with, it has a reputation for being used in low cost eyewear. Best avoided if you have sensitive skin and/or are prone to reactions with metal.
See also: Hinge | Joint | Rivet
Nose bridge
The crossbar section in the middle of a glasses frame which overhangs your nose.
See also: Bridge | Nose pad | Pad bridge | Bridge bumping
Nose pad
There for comfort, these small sections of your glasses rest on your nose for comfort and to secure the glasses on your face.
The pads are either inbuilt as part of an acetate frame front or pushed-in as a separate piece. Push in pads have the ability to be bent and adjusted whilst acetate pads are virtually impossible to break.
For instances of extreme adjustment, acetate nose pads may be reduced or entirely removed by hand-filing them away.
To compensate for medical scenarios such as facial disfigurement, nose pads may be enlarged via the addition of push-in nose pads.
Asian-fit glasses frames are known to have heightened nose pads to make them more comfortable to wear.
See also: Pad bridge | Projection of bridge
O
Ocular centre
Your ocular centres (OC's) are the location of your pupils behind a specific pair of glasses lenses. This is measured using a combination of a horizontal and vertical measurement known as pupillary distance and ocular height.
Vertical: Noted in mm, your eye's ocular heights are established by measuring from the bottom of your lenses to the part of the lens which aligns directly with your pupils.
Horizontal: Also in mm, your pupillary distance is measured using a specific ruler called a pupillometer or PD ruler to record the horizontal distance between your pupils.
Together, these measurements are crucial for optical accuracy, particularly for varifocal glasses wearers.
Measuring ocular height for varifocals
See also: PD | PD Ruler | Interpupillary distance | Dual PD | Single PD | Average PD | Centration | Ocular height
Ocular height
The distance in mm from the bottom of your lens to the centre of each pupil.
This measurement is used in conjunction with pupillary distance to correctly align your pupil with the optical centres of your lenses. Ocular height is measured for both eye on a frame by frame basis.
How to measure your ocular heights
See also: OS | OU | Prescription paper | SPH | CYL | Axis | ADD | Prism
OD / Oculus dexter
An optical abbreviation for oculus dexter. This is a Latin phrase for "right eye" and can be written on your prescription paper to precede your right eye's optical information.
See also: OS | OU | Prescription paper | SPH | CYL | Axis | ADD | Prism
OS / Oculus sinister
An optical abbreviation for oculus sinister. This is a Latin phrase for "left eye" and can be written on your prescription paper to precede your left eye's optical information.
See also: OD | OU | Prescription paper | SPH | CYL | Axis | ADD | Prism
OU / Oculus uterque
An optical abbreviation for oculus uterque. This is a Latin phrase for "left eye" and can be written on your prescription paper which precedes information about both your eyes.
See also: OD | OS | Prescription paper | SPH | CYL | Axis | ADD | Prism
Oleophobic
Part of MAR lens coatings, an oleophobic lens coating is a nano-layer which repels oil and grease from the surface of your lenses. This makes them easier to clean and helps to repel dust and dirt.
See also: Hydrophobic | HMC | MAR | Anti-reflective | Anti-glare | Anti-scratch | Refractive index
Optical centre
The geometric centre of a curved lens. This is the absolute apex of the lens which is aligned with your pupil according to your pupillary distance, ocular height and distance between lenses
See also: Pupillary distance | Ocular centre | DBL | Centration
P
Pad bridge
An acetate frame front with either a regular or keyhole bridge which have inbuilt pads. These humped pads rest on your nose and are tapered for comfort.
See also: Nose pad | Regular bridge | Keyhole bridge
Pad printing
A method of detailed ink printing used to mark the inner surface of glasses frames, glasses temple and on the surfaces of demo lenses.
Pad printing is a versatile marking method used in spectacle manufacture to achieve very fine and accurate lettering for details such as frame dimensions, CE marking and branding.
Learn about glasses frame markings
See also: Frame dimensions | Laser etching | CE mark | Demo lenses
Paddle temple
A glasses temple (arm) which is completely straight. It may curve inwards around the end but does not hook down around the ear. A paddle temple may also be refereed to as a blade temple.
See also: Blade temple | Hockey end | Drop end | Temple | Tip | Wire core
Pantoscopic tilt
The refers to the angle of your lenses from the vertical plane. The Pantoscopic tilt can vary between 0-12 degrees in one direction only. As the tilt increases the bottom of the lens is then closer to your cheeks.
See also: Let back
PD ruler
Also called a “pupillometer” or “PD stick”, this is an optical ruler used to measure the distance between each of your pupils.
See also: Pupillary distance | Interpupillary distance | Dual PD | Single PD | Average PD | Ocular centre | Centration
How to measure your pupillary distance
Photometer
Also called a “light meter."
In optics, a photometer is a electronic device used to measure the intensity of light before and after it enters a lens. Using a photo-diode, it can calculate how much light is transmitted through a lens.
Learn about visible light transmittance
See also: Absorption percentage | Visible light | Visible light absorbtance | Visible light reflectance | Visible light transmission | UV | Tint
Plano lens
A lens without any visual correcting power, optically referred to as PL for short or 0.00. Plano lenses are generally fitted for retail display purposes or if you require no optical correction in at least one of your eyes.
More information about plano lenses
See also: Aspheric lenses | Double aspheric lenses | Lens | Glass lenses | Crown glass | CR39 lenses | Demo lenses | Polarised lenses | Polycarbonate lenses | Refractive index | Trivex lenses
Polarised lenses
Polarised lenses are a type of sunglasses lens which have an inbuilt chemical film within the layered lens construction. This film is called a polariser which acts as a filter to largely diminish reflected glare from reflective surfaces such as water or snow.
See also: Absorption percentage | Gradient lens tint | Tint | Sun lens category | Lens | UV | Visible light | Visible light absorbtance | Visible light reflectance
Polycarbonate lenses
Developed in the 1970’s, polycarbonate lenses are lightweight and highly impact resistant and are commonly used for safety or children’s eyewear. Instead of being casted, polycarbonate lenses are injection moulded.
It is advisable that polycarbonate lenses are always coated with an anti-reflective lens coating to reduce glare across the lens surface.
See also: Aspheric lenses | Double aspheric lenses | Lens | Glass lenses | Crown glass | CR39 lenses | Demo lenses | Refractive index | Trivex lenses | Refractive index
Polymer
The chemical term for plastic.
Polymers comprise of a large amount of monomers which are bonded together in a process called polymerisation. Polymers can either be organic or synthetic depending on the source of their monomers.
In the context of eyewear, polymers can be used to make ophthalmic lenses or the actual spectacle/sunglasses frame itself. CR39, polycarbonate or Trivex lenses are all example of polymer-based lenses.
Cellulose acetate is a semi-synthetic polymer as it’s main component is the cellulose from cotton of wood pulp.
Another example of a semi-synthetic polymer is Galalith; a bio-plastic made using cow's milk.
See how cellulose acetate is made
See also: Acetate | Bone glasses | Baleen glasses | Ebonite glasses | Gold glasses | Galalith | Ivory glasses | Leather glasses | Tortoise shell glasses | Shagreen glasses | Wooden glasses
Presbyopia
This common condition which tends to occur during middle age.
The ciliary muscles in your eye begin to weaken whilst the crystalline lens in your eye begins to harden. Simultaneously, these affects hinder your ability to see things closely which is the main cause for wearing reading glasses.
See also: Reading glasses | Ciliary muscles | Zonules | ADD | Close vision
Prescription paper
This is where your biennial eye examination details are documented.
Every two years, you're advised to take an eye examination. This is to examine the health of your eyes and they're ocular capability. After the test, your prescription paper is provided to you which states any deficiencies and/or the condition of your eyes.
These details are listed separately for each eye and contain optical abbreviations like those listed in the "See also" section below.
See also: ADD | Axis | CYL | Prism | SPH | OD | OS | OU
Prescription reading glasses
Unlike ready reader glasses, prescription reading lenses offer your unique SPH and CYL for each of your eyes. This means each lens can be a different power to suit your unique requirements for assistance with close reading (presbyopia.)
Ready reader glasses are the same power in each lens and don't cater for your pupillary distance.
8 reasons to invest in high quality reading glasses
See also: Ready reader glasses | SPH | CYL | Pupillary distance | Prescription paper
Prism
Found on your prescription, these digits refer to the amount of prismatic power your eye/s require in order to correct the misalignment of your eyes.
This is used to alleviate eye strain to make your eyes work together in unison. Written either as 0.5 or ½ , prism may be prescribed in on or both eyes but is relitively uncommon.
See Prism on prescription paper
See also: ADD | Axis | CYL | SPH | PD | Single PD | Dual PD | Prescription paper
Projection of bridge
Think of this as the total height of the acetate pads that protrude from the surface of the frame front.
This is measured from the face of the frame backwards to the apex of the sculpted pad. This is generally in the region of 5-10mm but for Asian fit frames, it can be as much as 16mm.
See also: Nose bridge | Pad bridge
Pupil
The aperture on the front of your eye which allows light to strike the retina. The dilation (width) of your pupil is controlled via your iris.
See also: Cornea | Cilliary muscles | Iris | Zonules
Pupillary distance
This is the horizontal distance between the centres of each of your pupils.
Known as PD for short, pupillary distance can be assessed as a single or dual PD measurement and is always measured in mm. An accurate PD measurement is required to align the optical centre of each lens with your pupil.
How to measure your pupillary distance
See also: PD | PD Ruler | Interpupillary distance | Dual PD | Single PD | Average PD | Ocular centre | Centration
R
Reading glasses
A glasses frame fitted with ready reader or prescription reading lenses to correct the affects of presbyopia.
See also: Ciliary muscles | Zonules | Presbyopia | ADD
Ready reader glasses
Frames with ready reader lenses have matching focal powers. These are measured in dioptres ranging from +1.00 up to +3.50 increasing in +0.25 increments.
Ready readers are intended as a low cost solution to assist your close reading and are something of a "one size fits all". This is because the lenses do not individually cater for your unique SPH, CYL or pupillary distance.
To calculate your ready reading glasses lens strength, click here.
See also: Prescription reading glasses | Close vision | Presbyopia | CYL | SPH | ADD | Pupillary distance
Refractive index
(RI) refers to the relative speed of light within a spectacle-lens compared to that inside a perfect vacuum. In other words, this describes how efficient as lens is at bending light.
As a rule of thumb, the higher the refractive index, the thinner and lighter a spectacle lens can be. This is why high-index lenses are preferred if you have a particularly strong prescription, as it helps to reduce bulky "milk bottle" lenses.
RI can be measured with various lens substrates whether it’s a plastic or a glass lens. Depending on their material, spectacle lenses vary in refractive index from 1.50 to 1.90.
See also: Abbe | Demo lenses | High index lenses | Low index lenses | Lens thinning | Lens | CR39 | Plano lens | Polarised lenses | Polycarbonate lenses | Trivex lenses
Regular bridge
This term refers to the bridge shape looking directly at the frame front. Unlike a keyhole bridge, a regular bridge is simple, swept and continuous without any detail. For acetate frames, this bridge type is considered more modern.
See also: Keyhole bridge | Pad bridge | Bridge bumping | Projection of bridge | Acetate
Retina
Light sensitive tissue within your eye. Your retina translates light into neural impulses which are sent to your brain via your optic nerve.
See also: Cornea | Ciliary muscles | Iris | Pupil | Zonules
Rhodoid
A trade-name for cellulose acetate, trademarked by "May & Baker" in Wandsworth, London. It's rudimentary properties consist of purified cellulose and acetic acid which is then coloured using dispersing dyes.
See how cellulose acetate is made
See also: Acetate | Block acetate | Cellon | Celluloid | Cellulose | Curing | Disperse dye | Ebonite | Galalith | Polymer | Tenite | TR90 | Xyl | Zyl
Rimless
A frame that has no outer-rim. Instead, the temples are joined to the lenses using screws. The lenses are then joined with a metal bridge which is, again, screwed through each lens at the edges.
See also: Full rim | Half rim | Lens groove | Bevel | Glazing | Supra
Rivet
A cylindrical piece of metal used to fasten hinges to the frame front or temples via a process called peening or staking.
Rivets from glasses making can be parallel or tapered and are usually made from soft metal such as steel, brass or nickel alloy.
Parallel rivets have a head on them to prevent the rivet from coming loose.
See also: Staking | Riveting | Rivet head | Rivet shank | Rivet hole | Hinge grave | Hinge | Joint
Riveting
The process of permanently fastening the rivets which secure the hinges of glasses frames.
Since 2000 BC, riveting is a rudimentary process which involves the deformation of a rivet in order to secure two or more parts of material together. For glasses, small metal rivets are inserted through the horn or acetate frame front and the hinge.
The rivet is then squashed/domed using using a peen and hammer, with a staking tool or a electro-pneumatic machine.
This method permanently fastens the hinge to the frame front, usually within a shallow recess called a hinge grave.
See also: Staking | Hinge | Hinge grave
Rivet head
The top of a rivet which is visible on the surface of the glasses end-piece. Usually, for aesthetics, rivet heads are polished "flush" to match the surface of the frame-front.
See also: Rivet | Rivet hole | Rivet shank | Riveting | Staking | Hinge | Joint | Half joint
Rivet hole
Where the hinge rivets locate through the glasses frame front, prior to fastening the hinges down via riveting.
See also: Rivet | Rivet head | Rivet shank | Riveting | Staking | Hinge | Joint | Half joint
Rivet shank
Under the rivet head is the shank. This is the long, uniform portion of the rivet which passes through the frame front.
See also: Rivet | Rivet hole | Rivet head | Riveting | Staking | Hinge | Joint | Half joint
Round-Seg lens
A bifocal lens which contains a circular close-reading segment within the lower section of the lens.
Learn more about bifocal glasses
See also: Franklin lens | D-Seg | Bifocal lenses
S
Screw
Either a cross-head dowel-head used to join the frame front to the temples via the hinge. Slot-head screws are also called “dowel screws.”
Screws for glasses are generally standard, ranging from 0.8 to 1.2mm in diameter using a right-hand thread.
As these screws are so small, they sometimes come with a detachable stem. In the industry, screws like these are called "thread seekers" which helps them locate into the threaded charniers of a hinge
Once located, the stem can be easily snapped off by hand.
See also: Thread seeking screw | Dowel screw | Cross head screw | Hinge | Joint | Charnier | Frame front | Temple
Shagreen glasses
Glasses frames made from the skin from sharks or rays. Although this material have been occasionally referenced, shagreen glasses have not been properly recorded. Physical examples are non existent.
See also: Acetate | Bone glasses | Baleen glasses | Ebonite glasses | Gold glasses | Ivory glasses | Leather glasses | Tortoise shell glasses | Wooden glasses
Sides
The optical term to describe the temples of a glasses frame. Colloquially called legs or arms, the sides of a frame are named in unison with the front (frame front.)
See also: Temple | Frame front
Side shields
Plastic or traditionally made from leather, side shields are used to shroud the edges of a sunglasses frame.
Intended to reduce light and dust from entering your eyes, they close the gap between your face and the frame. This addition further prevents light and dust from entering your eyes, either from the sides or from above.
Side shields can be added to the frame by either hooking over the frame and temples or by being moulded as part of the frame itself.
See also: Temple | Frame front
Single PD
This is the total distance between your pupils and is measured in mm. Eg: 64mm. Dual PD is measured from the centre of your nose to your pupil and is noted separately for each eye.
See also: Dual PD | Average PD | PD | PD ruler | Ocular centre | Centration
Single vision lenses
These lenses correct your vision at a single distance which can be for near, intermediate or distance applications.
Single vision lenses are most commonly prescribed to correct your short or long sightedness, otherwise known as myopia or hyperopia. Generally, single vision lenses are to help you with tasks such as reading, computer work or for driving.
Multifocal lenses contain more than one prescription per lens. These can be bifocal, trifocal or varifocal lenses.
See also: Anti-fatigue lenses | Myopia | Hyperopia | Bifocal lenses | Reading glasses | Varifocal glasses
Staking
The process of permanently fastening/fixing a metal rivet. This can be done via a hand-held peen or with a staking tool otherwise known as a clavulus.
See also: Riveting | Rivet | Tumble polishing | CNC Machining | Frame curving | Bridge bumping | Hand polishing | Ultrasonic cleaning
SPH / Sphere
The first box seen on your prescription details, you’ll notice the term SPH followed by positive or minus digits. This value denotes the dioptric strength required to correct your myopia or hyperopia.
See also: ADD | Axis | CYL | Prism | Hyperopia | Myopia | Prescription paper
Spheric lenses
Also known as spherical lenses, there are the simplest form of lens which use a singular curvature across its front surface profile.
Spherical vs aspherical lenses
See also: Abbe | Aspheric lenses | Double aspheric lenses | Low index lenses | Refractive index | Spheric lenses | High index lenses | HMC | MAR | Anti-reflective | Anti-glare | Oleophobic | Hydrophobic
Splay angle
The angle of the nose pad on the rear of the frame front which provides facial comfort and allows the frame to rest/grip onto your nose. The angle is measured from the inside of the frame against the nose pad, usually around 60 degrees.
Spring hinge
A hinge with an in-built spring mechanism which allows a greater amount of let back angle. Onece the temple and frame have met, the spring allows the temple to go beyond its maximum, thus making them more of a one size fits all.
NB: Spring hinges are common in low cost ready reader frames as a way of maximising the chances of comfort for a wider range of people.
Solid, tenon-hinges do not spring and require skilled hand-filing to adjust the let back of a glasses frame. Tenon hinges are more traditional but they provide a more stable, more durable construction.
See also: Let back | Hinge | Hidden hinge | Joint | Screw | Thread seeking screw | Dowel screw | Cross head screw
Sun lens category
Sunglasses lenses are categorised by darkness of tint.
There are five categories in total which transmit measurably different amounts of light through the lens. These tints range from very light (category 0) to extremely dark (category 4.)
|
Category |
0 |
1 |
2 |
3 |
4 |
|
ABS% |
0% - 10% |
10% - 20% |
20% - 43% |
43% - 85% |
85% – 92% |
|
Tint |
Very light |
Light |
Marginal |
Dark |
Very dark |
|
Sun use |
Overcast |
Low |
Moderate |
Strong |
Very strong |
|
Driving suitability |
Day & night |
Day only |
Day only |
Day only |
Never |
See also: Absorption percentage | Visible light transmission | Visible light absorbtance | Visible light reflectance | Visible light | UV | Tint
More about sun lens categories
Supra
A thin nylon chord to secure a lens within a half-rim glasses frame.
Supra chord is comparable to fishing-line as it's transparent and has a very fine diameter of less than 1mm. The chord locates into a V shaped recess on the edge of the lens which is threaded through the frame and pulled tight. This tension is what holds the lens into the frame.
See also: Half rim | Full rim | Glazing | Lens groove | Bevel
T
Tenite
A trade name for cellulose acetate, manufactured distributed by "Eastman Chemical." The name was first trademarked in 1932. Very much the same as cellulose acetate, Tenite has been used for the production of glasses making. It's rudimentary properties consist of purified cellulose and acetic acid which is then coloured using dispersing dyes.
See how cellulose acetate is made
See also: Acetate | Block acetate | Cellon | Celluloid | Cellulose | Curing | Disperse dye | Ebonite | Galalith | Polymer | Rhodoid | Tenite | TR90 | Xyl | Zyl
Tenons
Part of a glasses hinge, tenons are the threaded metal loops which protrude from the base-plate of the glasses hinge.
Also called charnier, chenier or barrels, the hinge-tenons interlock with one another and are secured with a threaded dowel screw. Hinges vary in tenon counts ranging from a three-tenon, five-tenon and occasionally a seven-tenon.
See also: Charnier | Hinge | Hidden hinge | Half joint | Joint | Dowel screw | Cross head screw | Thread seeking screw
Temple
Colloquially known as the arms or legs of a glasses frame, the temples are the thin protrusions that help secure the glasses to your head by resting and hooking behind your ears.
Optically speaking, they can also be called “sides” for obvious reasons. There are various types of temple such as a blade temple, paddle temple, curl temple, drop-end temple, hockey-end temple, loop-end temple, earjoy temple, sinous temple or suspension temple. All these terms refer to the shape, material or function.
See also: Frame front | Blade temple | Paddle temple | Drop end | Curl sides | Tip | Wire core
Temple length
Usually pad printed or laser etched onto the inside of the temple.
This measurement is written in as the third in the series of digits that indicate the dimensions of a glasses frame. (Eg: 52 [] 18 135) Temple length vary between children’s, women’s and men’s frames, ranging from 120mm to 160mm.
Learn about glasses frame dimensions
See also: Bridge width | Frame dimensions | Lens diameter | Pad printing | Laser etching
Thread seeking screw
A glasses screw with an extended tip.
Also called thread seekers, the extended tip makes it easy to locate the screw into the glasses hinge. Once the screw is located, you can tighten it into place using a screwdriver.
At this point, the tip will extrude from below the glasses hinge which allows it to be carefully bent and snapped off.
See also: Dowel screw | Cross head screw | Hinge | Joint
Tint
A tint is method of applying a darkening coat to the surface of a lens to reduce the amount of light that is transmitted through it.
By doing so, tinted lenses become suitable as sun lenses so long as they block 99-100% of UV light. Different colours of tint can be achieved at varying levels of darkness.
See also: Absorption percentage | Visible light transmittence | Visible light | Visible light absorbtance | Visible light reflectance | UV | Polarised lenses | Gradient lens tint
Tip
The end-point of the temple, furthest away from the frame front. Frame chains may be attached to temple tips as a way of wearing your glasses around your neck.
See also: Temple | Temple length | Drop end | Paddle temple | Blade temple | Wire core
Tortoise shell glasses
(Not to be confused with imitation, acetate, tortoise shell.)
Common between the 18th and 20th century, the shells of hawksbill turtle (protected) was used to make spectacle frames with. It had similar properties and aesthetics to horn and could be moulded under heat into the correct shape.
Tortoise shell for glasses was banned in 1973 by the Convention of International Trade in Endangered Species (CITES.)
See also: Acetate | Bone glasses | Baleen glasses | Ebonite glasses | Gold glasses | Ivory glasses | Leather glasses | Shagreen glasses | Wooden glasses
Trifocal lenses
An optical lens with three separate lens segments which cater for close, intermediate and distance vision. Each segment makes a third of the lens, starting with close vision at the bottom segment.
See also: Anti-fatigue lenses | Bifocal lenses | Varifocal glasses | Single vision lenses
Triple rivet hinge
A metal hinge, also called a joint, which is fastened using three rivets through the frame front and three through the temple. This style of hinge is large and rather dominant but provides a durable connection and charming aesthetic.
See also: Double rivet hinge | Hinge | Joint | Spring hinge | Hidden hinge | Hinge grave | Riveting | Staking
Trivex lenses
Introduced in 2001, Trivex lenses have comparable properties to polycarbonate lenses.
They are cast-moulded and have exceptional impact resistance and are 100% UV protective. However, Trivex lenses have a slightly lower refractive index than polycarbonate which makes them marginally thicker.
See also: Aspheric lenses | Double aspheric lenses | Lens | Glass lenses | Crown glass | CR39 lenses | Demo lenses | Plano lens | Polarised lenses | Polycarbonate lenses | Refractive index
TR90
TR90 is a flexible thermoplastic material used for mass producing eyewear via injection moulding. Typically associated with sports sunglasses frames, it's known to be durable, lightweight and impact resistant.
For these reason, TR90 is particularly suited for active individuals and children, its hypoallergenic properties make it an ideal choice for those with sensitive skin. The rubber-like texture and matte finish not only add to its aesthetic appeal but also enhance its grip, preventing the eyewear from slipping during vigorous activities.
See also: Block acetate | Cellon | Celluloid | Cellulose | Curing | Disperse dye | Ebonite | Galalith | Polymer | Rhodoid | Tenite | Xyl | Zyl
Tumble polishing
Acetate frame fronts and temples are polished inside large octagonal wooden barrels which contain wooden chips and polishing compound.
Via electric motor, the barrels continuously rotate, thus tumbling the frames over and over to rid them of their rough edges and imperfections.
Over several days, this process makes them smooth and comfortable to wear.
See also: Hand polishing | CNC machining | Ultrasonic cleaning
U
Ultrasonic cleaning
A cleaning process which removes oil, wax, dirt and grease from the frame front and/or the temples.
These components are placed inside a tank of water which is added with cleaning fluid and marginally heated to 40°C. Inside the tank ultrasonic waves are then induced to agitate the water.
This loosens and removes any dirt from the parts which come from previous processes such as CNC machining, tumble polishing or hand polishing.
See also: CNC machining | Tumble polishing | Hand polishing
Uni-piece Temple
Unique to Banton Frameworks, our uni-piece temple is precision machined from a single piece of steel. Restrained to a single part, we’ve reduced the amount of components in their construction which makes them smooth to wear and understated in aesthetic.
See also: Temple | Tip | Drop end | Hockey end | Blade temple | Paddle temple | Wire core
UV40
A sun lens rating which refers to its ability to block UVA and UVB light to 400 nano metres in compliance to European standard: EN 1836:2005
See also: UV | UV400 | Tint | Polarised lenses
UV400
A sun lens rating which refers to its ability to block UVA and UVB light to 400 nano metres in compliance to European standard: EN 1836:2005
UV | UV40 | Tint | Polarised lenses
Ultraviolet light
This defines the portion of light within the electromagnetic spectrum between 10 and 400 nano metres (nm).
With regards to skin and eyecare, there are within the dangerous range of electromagnetic radiation and therefore should be blocked by sufficiently rated sunglasses.
In compliance with British and European standards, sunglasses lenses must block 99-100% of UV light up to 380nm to bear the internationally recognised CE mark.
However, many sunglasses are rated as UV400 which means the block 99-100% of UV light up to 400nm.
|
UV light sub-type |
Frequency (nm) |
Danger to eyes & skin |
|
UVA |
315 - 400 |
High |
|
UVB |
280 - 315 |
Medium |
|
UVC |
100 - 280 |
Low |
See also: CE mark | Polarised lenses | UV400 | Visible light absorbtance | Visible light reflectance | Visible light transmittence | Sun lens category
V
Varifocal glasses
Also called progressives, varifiocal lenses contain a progression of visual powers from the top to the bottom of the lens.
Unlike bifocal lenses, varifocals have no defining split-lines within the lens. Instead they transition from close reading in the lower section of the lens, to distance vision in the upper.
See also: Anti-fatigue lenses | Bifocal lenses | Single vision lenses | Trifocal lenses
Visible light
This is the visible portion of the electromagnetic light spectrum which can be seen by the human eye ranging between 400nm to 700nm.
Affectionately, it consists of the colours of a rainbow which are initialised and often referred to as ROYGBIV; Red, orange, yellow, green, blue, indigo and violet.
UV light has a range less than 400nm which is invisible to the human eye, which is why it differs to visible light.
Sunglasses block 99-100% of UV light whist also reducing the amount of visible light that passes through each lens (depending on the darkness of tint).
What are the 5 sunglasses categories?
Learn about visible light transmittance
See also: Absorption percentage | Visible light absorbtance | Visible light reflectance | Visible light transmittance | UV | Tint
VLA / Visible light absorbtance
This is the amount visible light absorbed by a spectacle or sunglasses lens. Abbreviated as VLA or ABS, this value is measured as a percentage.
Learn about sun lens categories
See also: Absorption percentage | Visible light | Visible light reflectance | Visible light transmittence | UV | Tint
VLR / Visible light reflectance
This is the amount visible light reflected by a spectacle or sunglasses lens. Abbreviated as VLR, this value is measured as a percentage.
Learn about visible light transmittance
See also: Absorption percentage | Visible light | Visible light absorbtance | Visible light transmittance | UV | Tint
VLT / Visible light transmittance
Visible light transmittance is the amount of light that can pass though a spectacle or sunglasses lens.
- Lenses with 99% VLT are considered as white, meaning it is completely transparent.
- Lenses with 1% VLT are considered as black, meaning it is very dark to look through.
Arguably, VLT can be a personal preference however is largely determined by your intended application. For tasks such as driving, lenses with a VLT of 8% or less are illegal to wear.
The table below describes how VLT places sunglasses into one of five categories.
|
Category |
0 |
1 |
2 |
3 |
4 |
|
VLT% |
80% - 100% |
43% - 80% |
18% - 43% |
8% - 18% |
3% – 8% |
|
Tint |
Very light |
Light |
Marginal |
Dark |
Very dark |
|
Sun use |
Overcast |
Low |
Moderate |
Strong |
Very strong |
|
Driving suitability |
Day & night |
Day only |
Day only |
Day only |
Never |
Learn about visible light transmittance
See also: Absorption percentage | Visible light absorbtance | Visible light reflectance | Tint | Gradient lens tint | Polarised lenses | UV
Virtual mirror
A digital application which you can use to virtually try-on our spectacles and sunglasses frames.
Via the web-cam on your smart-phone, tablet or computer, our glasses/sunglasses frames are visually projected onto your face in real-time. This app allows you to assess if a particular frame shape suits you prior to trying them at home.
Learn more about the virtual mirror
See also: Home try on | Klarna
W
Wire core
A a thin section of reinforcing metal which is forcefully injected into an acetate temple via heat and pressure.
The core’s purpose is to preserve curvature and adjustments as it’s less malleable than the acetate that surrounds it.
See also: Frame heating | Temple | Tip | Blade temple | Curl sides | Drop end | Hockey end | Paddle temple
Wooden glasses
Interspersed throughout the history of spectacles, wood has been an ever-present choice of material to make glasses frames. Since the 13th century to the present day, timber from beech, birch or lime trees have been used to make glasses frames and temples.
See also: Acetate | Bone glasses | Baleen glasses | Ebonite glasses | Horn glasses | Gold glasses | Ivory glasses | Leather glasses | Tortoise shell glasses | Shagreen glasses
X
Xyl
The UK trade name for Zyl, "Xyl" was a branded product line of cellulose acetate made in America by the "American Zylonite Company."
See how cellulose acetate is made
See also: Acetate | Block acetate | Cellon | Celluloid | Cellulose | Curing | Disperse dye | Ebonite | Galalith | Polymer | Rhodoid | Tenite | Zyl
Z
Zonules
Tiny ligaments that suspend the the crystalline lens within your eye.
See also: Ciliary muscles | Iris | Cornea | Pupil
Zyl
Also called zylo or zylonite.
Zyl is an 1800's American trade name for a type of cellulose polymer, similar to that of acetate. In the UK, this trade name was written as Xyl.
See how cellulose acetate is made
See also: Acetate | Block acetate | Cellon | Celluloid | Cellulose | Curing | Disperse dye | Ebonite | Galalith | Polymer | Rhodoid | Tenite | Xyl