Eyewear Glossary

Every term you are likely to meet when choosing frames and lenses, in plain English. If a word on a product page or in your eye-test results is not here, ask our specialist team.

Frame parts · Sizes and measurements · Reading your eye-test results · Lenses · Materials · Shapes and styles

Frame parts

Front
The main part of the frame that holds the lenses, made up of the two rims and the bridge.

Rim
The part of the front that surrounds each lens. Frames can be full-rim, semi-rimless (supra) or rimless.

Bridge
The part of the front that sits over your nose and joins the two lenses. Its width is the middle of the three numbers on the temple.

Keyhole bridge
A bridge shaped like an upside-down keyhole, so the frame rests on the sides of the nose rather than across the top. Common on classic acetate frames.

Double bridge
A second bar across the top of the front, above the main bridge. A signature of aviator-style frames.

Nose pads
Small adjustable pads, usually on metal frames, that rest on the sides of the nose. They let a frame be fine-tuned to sit at the right height.

Temple
The arm of the frame that runs from the front to behind your ear. Its length in millimetres is the last of the three size numbers.

Hinge
The joint between the front and the temple. Spring or flex hinges open slightly wider than normal for a more forgiving fit.

Temple tips
The ends of the temples that sit behind the ears, sometimes with a softer coating for comfort.

Sizes and measurements

Eye size (lens width)
The horizontal width of one lens in millimetres, and the first of the three numbers inside the temple, for example the 54 in 54-18-145.

Bridge width
The distance between the two lenses in millimetres; the middle number of the three.

Temple length
The length of the arm in millimetres; the last of the three numbers.

Frame width
The overall width of the front from hinge to hinge. We list it on each product page because it is the best single guide to whether a frame will suit the width of your face.

Lens height
The vertical depth of the lens. Deeper lenses give more coverage; shallower ones suit a lighter, more minimal look.

PD (pupillary distance)
The distance between the centres of your pupils in millimetres. It tells the lab where to place the optical centre of each lens. It can be a single number or two (one for each eye).

Engraved size
The size printed on the frame itself. Occasionally a brand uses a slightly different nominal size in its product codes; we always show the size engraved on the frame.

Reading your eye-test results

SPH (sphere)
The main lens power, in dioptres. A minus number corrects short sight; a plus number corrects long sight.

CYL (cylinder)
The extra power needed to correct astigmatism, where the eye focuses differently in different directions. If it is blank, there is no astigmatism to correct.

AXIS
A number from 0 to 180 that tells the lab the direction of the cylinder. It only appears when there is a CYL value.

ADD
Extra reading power for close work, used in varifocal and reading lenses. Online, our lenses are single vision.

Prism
A correction that shifts the image to help the eyes work together. It is written in prism dioptres with a direction (up, down, in or out).

Dioptre
The unit used to measure lens power. Higher numbers, plus or minus, mean stronger lenses.

Single vision
A lens with one power across the whole lens, for distance, reading or a computer distance. All the optical lenses we make online are single vision.

Varifocal
A lens with a gradual change of power from distance at the top to reading at the bottom.

Lenses

Lens index
A measure of how strongly the lens material bends light. A higher index (1.6, 1.67, 1.74) can be made thinner and lighter than a standard 1.5 lens for the same power.

Optical centre
The point of the lens where your vision is clearest and there is no prismatic effect. It is placed in line with your pupil using your PD.

Zero-power (plano) lens
A lens with no correction, used when you want the look of a frame, or sun lenses, without changing your vision.

Anti-reflection (AR) coating
A coating that reduces reflections on the front and back of the lens, so the lens looks clearer and you see fewer distracting reflections.

Hard coat
A scratch-resistant coating applied to the lens surface.

Blue-light filter
A coating or lens material that reduces some of the blue-violet light from screens and lighting.

Photochromic
A lens that darkens in UV light and clears again indoors. Transitions® is the best-known brand.

Transitions®
A brand of photochromic lens that is clear indoors and darkens outdoors. Because it reacts to UV, it darkens less behind a car windscreen.

Transitions® Colour Touch
A Ray-Ban Transitions® lens with a soft tint of colour indoors that deepens outdoors, as a wash or a gradient.

Polarised
A sun lens with a filter that blocks horizontally reflected glare from water, roads and glass, giving clearer, more comfortable vision in bright conditions.

Tint
A colour added to the lens. A solid tint is one even colour from top to bottom.

Gradient
A tint that is darker at the top and fades towards the bottom, useful for driving and reading a dashboard or phone.

Mirror
A reflective coating on the front of a sun lens that reduces the light reaching the eye and gives a metallic finish.

G-15
Ray-Ban's classic green-grey sun lens, known for showing colours naturally.

B-15
Ray-Ban's brown sun lens, which adds warmth and contrast.

Prizm
Oakley's lens technology, tuned to enhance colour and contrast for particular environments, such as Prizm Road or Prizm Deep Water.

UV400
Protection that blocks ultraviolet light with wavelengths up to 400 nanometres, covering both UVA and UVB.

Ray-Ban Authentic lenses
Lenses made by Ray-Ban and signed with the Ray-Ban logo, with the complete pair made up by Ray-Ban. We offer them on Ray-Ban Meta frames.

Materials

Acetate
A plant-based plastic cut from sheets and polished, known for rich colours, depth and patterns such as tortoiseshell.

Propionate
A lightweight, flexible plastic that can be injection-moulded, used by Ray-Ban on several optical frames.

Nylon (injected)
A light, strong, slightly flexible plastic shaped by injection moulding, common in sunglasses and sports frames.

O Matter
Oakley's lightweight, flexible frame material.

Metal
Frames made from alloys such as stainless steel or monel, often finer and lighter in appearance than plastic.

Titanium
A very light, strong and corrosion-resistant metal used for premium lightweight frames.

Havana / tortoiseshell
A brown, mottled pattern inspired by tortoiseshell, now made in acetate or other plastics.

Shapes and styles

Full-rim
A frame whose rim surrounds the whole lens. The most robust option, and the easiest to glaze with thicker lenses.

Semi-rimless (supra)
A frame with a rim across the top only; the lens is held underneath by a thin nylon cord.

Rimless
Lenses fixed directly to the bridge and temples, with no rim at all.

Browline
A frame with a bold upper rim, like an eyebrow, and a slimmer lower rim. The Ray-Ban Clubmaster is the classic example.

Aviator (pilot)
A teardrop-shaped frame designed for pilots, usually metal with a double bridge.

Wayfarer
Ray-Ban's trapezoid plastic frame with a strong brow line, first introduced in 1952.

Panto (phantos)
A rounded frame with a slightly flattened top, sitting between round and oval.

Cat-eye
A frame that sweeps upwards at the outer top corners.

Butterfly
A larger, softly flared shape related to the cat-eye, wider at the top outer corners.

Pillow
A softened square or rectangle with rounded corners.

Wrap
A curved front that follows the shape of the face, common on sports sunglasses. Strongly wrapped frames can limit the optical lenses that can be fitted.

Keep exploring

Find your size · Ray-Ban Authentic lenses · Lens thickness explained · Polarised vs tinted lenses · Shop all eyewear