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Popular Eyecare Terms

Designer Glasses & Sunglasses | Popular Eyecare Terms

When refering to your prescription you may come across terms or abbreviations that you are not familiar with, below we have produced a glossary of the most popular terms to help assist you buy your perfect eyewear.

OD – This is shorthand for oculus dexter which means Right Eye.

OS – This is shorthand for oculus sinister which really means Left Eye.

Sphere (SPH) – This is the first section of your RX. It corrects nearsighted or farsighted vision and is written in +/- 0.25 increments.

Plano – PL – This indicates there is no spherical correction in this eye. A plano lens would have no focusing power or correction to it.

Balance – This indicates there is no vision correction in this eye. It’s a non-prescription lens and is used when only one of your eyes requires vision correction and the other one does not.

Cylinder – CYL – This indicates the amount of astigmatism, and is written in +/- 0.25 increments. Not all prescriptions have a cylinder correction, and some prescriptions have a cylinder correction in only one eye. If you don’t have an astigmatism correction then your doctor leaves this field blank.

 Axis (AX) – This is also part of the astigmatism correction, and is written in increments of 1 (one). If there is no cylinder, then there should be no axis. Since it’s a degree/angle, it will be represented as a value between 1 and 180. If there is an astigmatic correct then it is essential that there os and Axis noted on the prescription too as the two go hand in hand.

ADD – This is a value that is used for bifocal or progressive ( varifocal) lenses, as well as reading glasses. It indicates how much power gets added to the distance power in your prescription to create the reading zone.;  It is written in increments of + 0.25.

Prism or Base or Base Curve – A prism is used when both eyes are not properly aligned and they need a prism to re-align them. The Base is the rotation of the prism. These fields are rarely used. There are two separate parts to a Prism correction. The first part is the Prism strength (e.g. 2.0) and the second is the direction (e.g. BU). There are four different directions. Base-Up (BU), Base-Down (BD), Base-In (BI), and Base-Out (BO).

Pupilary Distance – PD – This is the distance in millimeters between your right pupil and left pupil. This is also essential information for your optical lenses to be made. A more detailed explanation of Pupillary Distance can be found in our Pupillary Distance (PD) page.

Fitting Segment Height – This is the vertical measurement in millimeters from the bottom of the lens to the  Pupil centre. Segment height does not apply to Single Vision lenses but for varifocal/ bi-focal / progressive lenses. You will need the frame to be able to measure segment height because you can only measure it while the glasses are on your head.

Near Vision or Near Vision Only – NV or NVO – This is written when your doctor is recommending reading-only glasses. (This is also known as farsighted)

Distance Vision or Distance Vision Only – DV or DVO – This is written when your doctor is recommending distance-only glasses. (This is also known as near-sighted)

Amblyopia – The medical term for lazy eye, which is a loss or dimness of vision without any apparent disease of the eye.

Antimetropia – The medical term for when one eye is Myopic and the other is Hyperopic.

Astigmatism – An optical condition that can cause blurry vision. This is corrected by a Cylinder and Axis correction on a prescription.

Bench Alignment – The standard adjustment of an eyeglass frame before it is custom fit to the customer.

Bend – The bend is where the temple curves behind the ear.

Binocular –v A term used to describe the simultaneous use of both eyes at the same time.

Bridge – BRG – The measurement in millimetres of the small connecting piece between the lenses of a frame.

Combination – These frames are made of both plastic and metal. They can have a metal front with plastic temples or other variations.

Compound Lens – A lens that contains both a sphere and cylinder

Cornea – The clear, transparent portion of the outer covering of the eyeball which covers the front part of the eye.

Crystalline Lens – Also known as just “lens”, it is a transparent and colourless body located towards the front of the eyeball. Its function is to bring rays of light to a sharp focus on the retina.

Dioptre – Unit to designate the refractive power of a lens.

Diplopia – The medical term for when someone sees one object as two, it is also called double vision.

Distance Between Centers – DBC – This is the distance from the geometric center of one lens to the geometric center of the other lens, measured in millimeters.

Distance Between Lenses – DBL – This is the measurement in millimetres between the lenses of a frame (Bridge size).

Effective Diameter – ED – The largest diagonal measurement of the lens that passes through the centre of the lens.

Emmetropia – The medical term for someone with 20/20 or better vision. This type of vision does not need correction.

End Pieces – The part of the frame that connects the temples to the frame front.

Frame PD or Geometric Center Distance (GCD) – This is the distance from the geometric center of one lens to the geometric center of the other lens, measured in millimeters.

Full Frame – A one piece frame usually composed of just one type of metal.

Geometric Centre – G – The centre of each lens within the frame.

Half Eye – Designed for reading.

Hinge – The hinge on a frame is made up of a screw and two pieces that have barrels., it is the part that connects the front of the frame to the temples/ arms of the optical frame.

Horizontal – A –The horizontal measurement of the lens for a specific frame, measured in millimetres.

Hyperopia – The medical term for someone with farsighted vision who is able see things that are distant or far away clearly, but need vision correction in order to see things that are near or close-up. Hyperopia is usually corrected with a prescription that has a positive (+) Sphere.

Keratitis Sicca – The medical term for dry eye.

Lens Index – This refers to the thickness of a lens, the higher the number is, the thinner the lens is. The number, e.g. 1.67 refers to the index (degree) of refraction the lens provides. This means how much the light that enters the lens is refracted (bent) as it passes through the lens.

Lensometer – An instrument which measures dioptric power, axis location, optical centre and prism of a lens.

Macular Degeneration – A deterioration of the macula which results in a gradual loss of central vision (the centre of your vision).

Monocular – Refers to only one eye.

Myopia – The medical term for someone with near-sighted vision who is able to see things that are near or close-up clearly, but need vision correction in order to see things that are distant or far away. Myopia is usually corrected with a prescription that has a negative (-) Sphere.

Ocular Height – OC – The measurement in millimeters from the center of the pupil to the bottom edge of the frame.

Oculus Uterque (OU) – Latin for both eyes

Ophthalmologist – A medical doctor who has extensive education and training in surgery, diseases, functions, and refractive errors of the eye.

Optician – A person who prepares and dispenses optical devices to fill the needs of the patient’s prescription. He or she also maintains these devices by making adjustments to them.

Optometrist – A person who is professionally trained and licensed to examine the eyes for visual defects, diagnose problems and impairments and prescribe corrective lenses or provide other types of treatment.

Pantoscopic Tilt – The tilting of a spectacle frame so that the top of the frame is farther away from the face than the bottom.

Presbyopia – The medical term for someone who needs vision correction in order to see things that are both close-up and far away. A Bifocal or Progressive prescription is used for this type of vision correction.

Progressive Additive Lens – PAL – The ADD value specifically for progressive lenses.

Refraction – The change in direction of light as it passes obliquely from one medium to another; such as the refraction of light as it passes through the crystalline lens (eye).

Retina – Light sensitive nerve tissue in the eye that converts images from the eye’s optical system into electrical impulses that are sent along the optic nerve to the brain. Forms a thin membranous lining of the rear two-thirds of the globe.

Retroscopic Tilt – The tilting of a spectacle frame so that the bottom of the frame is farther from the face than the top of the frame. Retroscopic tilt should be added to frames when they rest on the cheeks.

Rimless – Usually made of metal and made up of temples, end pieces, a bridge, and two lenses. The lenses are mounted to the bridge and end pieces, which creates the frame front.

Semi-Rimless – The eyewire on these frames does not go completely around the lens, instead it connects to both the end pieces and the bridge, and can be mounted in a variety of ways. The most common mounting uses a nylon cord to secure the lenses to the bridge and end pieces.

Shank – The longest portion of the temple.

Spatula – The temple spatula, also known as the temple tip, end, or earpiece, is the portion of the temple which extends from the bend to the end.

Strabismus – Also known as being cross-eyed, it is the failure of the two eyes to simultaneously look at the same object.

Temple – Temples are the component of the frame which rest over the ears to properly hold eyeglasses in place.

Vertex Distance – The distance from the back surface of a lens to the front of the cornea.

Vertical – A – The vertical measurement of the lens for a specific frame, measured in millimetres.

Thin Lenses –  Hi-Index lenses are 30-50% thinner than standard plastic lenses and are the lens of choice for those with high prescriptions – prescriptions shown as +/- 0.00 to 4.00. At a 1.6–index, you’ll be amazed at how thin your eyeglass lenses can be!

Extra Thin Lenses are lenses that are 45% thinner than regular plastic lenses at an index of 1.67. These lenses are recommended for prescriptions from +/-3.00 to +/- 6.00 for maximum results.

Hi-Index ultra-thin lenses are the thinnest lenses available on the optical market with an index of 1.74. These lenses are recommended for those with prescriptions +/-6.00 and above.


HC –  Hard coating can be applied to your lenses in order to make them more resistant to  scratches thus prolonging their lifespan

ARC – Anti-reflective coating helps reduce reflection on the surface of the lenses making them more pleasing to the people who are looking at you and more comfortable to wear.

SARC –  Super Hydrophobic Anti-reflective coating is and anti-reflective coating that also has water repellent properties, ideal for people in rainy climates

UV – Ultra violet protection from UVA and UVB rays. It can be added to all lenses on optical frames to ensure protection from these harmful sun rays

Mirror – Mirrored fashion coating on top of the lens to give the lens a flash look. This comes in various colours, from blue to pink to gold etc etc

Digital Blue –  An important protective coating against the Blue-violet light emitted from digital appliances which is today becoming more of a health threat. It is highly recommended for anyone who spends more than a couple of hours  daily on digital devices.

Transition Lenses –  Colour change lenses specially made to turn dark when exposed to UV light. When lenses are out of sunlight, they will rapidly become clear again. They also preserve the health of the eye by blocking 100% of harmful UV rays. These are ideal for people who move from  indoors to outdoors regularly as it combines sunglasses and optical frame sin one

Polarized Lenses – These are available for sunglasses lenses and greatly reduces the glare from the light reflected from very bright surfaces and make sunglasses more comfortable to wear

Tinted Lenses – Lenses that trasnfor yoru otpicla frame into a pair of sunglasses. Dark tint or perhaps a lighter one as a fashion statement or as an eye strain reliever. A 10% amber or yellow tint is best for activities requiring visual contrast and a 10% pink tint is recommended for people sensitive to light, especially for those suffering from migraine headaches. This tint is then combined with a UV coat to ensure protection against the harmful sun rays.

Multifocal / Progressive/ Varifocal Lenses – Multifocal lenses are lenses that have two or more lens powers allowing you to see objects at all distances, so they combine, distance, reading as well as intermediate vision (for comptuers)! They can be separated into two groups: bifocals and progressives/Varifocals. Bifocal lenses contain two fields of vision that are separated with a line between the two lenses. Progressive lenses, often called multifocal lenses or “no-line bifocals”, provide multiple fields of vision in one lens because they gradually change in power starting from the top half of the lens and changing in strength as your eye progresses downward.