Glossary

Anti-Reflective Coatings / Kodak Clean'N'CleAR Lens Coating
Up to 15% of light can be prevented from reaching your eyes by reflections on the surfaces of your lenses - common causes are bright lights, computers, car headlights and high lens prescriptions. These reflections can be distracting for you and for others looking at you. By treating the lens with an Anti Reflection coating these reflections can be dramatically reduced - allowing over 99% of light to reach your eyes. See Kodak Clean'N'CleAR Lens coating.
Aspheric
A lens that does not have the same curve over its whole surface i.e. it is not spherical. These lenses are thinner and flatter (and sometimes lighter) than their spherical equivalents.
Astigmatism
Distorted vision caused because the eye is not spherical i.e. it is more "rugby ball" than "football" shaped. Corrected by having two different curves on the back surface of the lens.
Axis
Used in a prescription to ensure that the cyl (see below) is correctly positioned. It is given in degrees, between 1 and 180.
Bifocal Lenses
Lenses with an additional segment each part having a different prescription: one usually for reading and one for distance. They have different names according to the reading segment shape e.g. flat tops, curve tops, - the additional segment has a flat or curve top.
Cylinder (CYL)
The extra power needed by the axis to correct astigmatism, with it direction denoted.
Dioptre
The unit used to measure the power in a lens. A lens with a power of 1 dioptre will have a focal length of 1 metre.
Dispensing Optician
Dispensing Opticians (sometimes referred to as DO's), are qualified to dispense, fit and supply spectacles. They cannot perform sight tests. Only Ophthalmic Opticians can do this. The main function of the DO is the interpretation of a patient's individual visual and fitting requirements and the translation of the prescription into specifications and instructions to which the optical manufacturer will work.
Glazing
The term used for cutting and fitting the lens into the frame. See 'How a lens is made'.
Heights
The positioning of the bifocal line or the optical centre for progressive and single vision lenses.
Hi-Index Lenses
These are lenses which are made of higher density materials than standard plastic or glass thus enabling them to be thinner, lighter and flatter. See Kodak Thin & Lite Lenses. Each material has a different index e.g. 1.56, 1.59, 1.6. 1.66. The higher the number, the denser the material - the thinner the lens.
Lens
An optical medium consisting of two polished surfaces which refract light as it passes through, thus changing the way that it reaches the eye.
Myopia/Short Sightedness
Vision is out of focus for distant objects - the further away the object the harder it is to focus on it. May need to wear glasses all the time or may need to wear only some of the time - specifically when concentrating on things in the distance e.g. TV or driving.
Photochromic Lenses
Lenses that darken in sunlight and clear in dim light or indoors. See Kodak SunSensors and InstaShades Lenses.
Polarised Lenses
A sun lens with a glare reducing layer running through it. See Kodak UVSun Lenses.
Polycarbonate Lenses
Polycarbonate lenses are up to 10 times more impact resistant than standard plastic. See Kodak Thin & Lite, and Tuff lenses.
Presbyopia
Age induced inability to see things at close range e.g. reading a newspaper. Commonly noticed from the age of 40. Is the result of the eye's crystalline lens losing its flexibility - correctable with single vision, bifocal or more usually varifocal lenses. These are also know as progressive addition lenses (PAL). See Kodak Progressive Lenses.
Prescription
The end result of an eye examination.
Progressive Addition Lenses
Lenses that, unlike bifocals have no visible dividing lines and are used for viewing at all distances as the power gradually changes down the lens from distance through intermediate to near vision. Also sometimes called varifocals or multifocals. See Kodak Progressive Lenses.
Ophthalmic Optician/Optometrist
Ophthalmic Opticians (sometimes referred to as OO's), also known as optometrists, are qualified to test sight and to prescribe and dispense spectacles and other optical appliances. They are trained to recognise abnormalities and diseases that are revealed in the eyes.
Refractive Index
The ratio of the speed of light in air, to the speed of light in a given substance. The higher the refractive index of a material the more it will bend light, so the less of it that is needed to correct a prescription - the result of which is a thinner lens.
Rimless
A frame which has no rims around the lenses. The lenses are drilled and the bridge and sides are fitted directly to them with small screws.
RLX Plus Lens Coating
A hard coat with a difference, instead of the coating put on to the lens, it is actually embedded into the lens when the lens is being made. Making it the "World's most Scratch Resistant Plastics lens coating".
Scratch Resistant Lenses
Plastic lenses with protection on the surfaces to help reduce scratches. See RLX Plus.
Segment
A clearly visible section in a lens which provides extra power for near vision as in a bifocal lens.
Semi-Finished Lenses
Where only one surface of the lens has been worked to a specific curve. The other side is "worked" to its final power in an optical laboratory. See 'How a lens is made'.
Single Vision Lenses
Lenses that correct a single refractive need e.g. distance lenses or reading lenses.
Tint
A colour on a lens. Reduces the quantity of light transmitted through the lens. The type and intensity of the tint selected determines the transmission (usually between 15% and 85%).
Ultra Violet Light (UV)
Invisible rays given off by the sun that are potentially harmful to the eye - may cause cataracts.
Variable Tints
Or photochromic lenses, darken in sunlight and clear in dim light or indoors. See Kodak SunSensors™ and InstaShades™ Lenses.

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