Bookmark Page ! About Us Terminology Contact Basket	From £29.95    Designer    Sunglasses    Contact Lenses   TERMINOLOGY Sphere The first number on your prescription, can either be + to indicate long sightedness or - to indicate short sightedness. Cylinder The second number in your prescription indicates the amount of astigmatism. Astigmatism is normally due to irregular curvature of the cornea. Axis A number that always follows the cylinder between 1 and 180 degrees to indicate the direction of the astigmatism. Add The Add, short for Reading Addition, is the additional correction required for reading, this could be used to make reading glasses, bifocal or varifocal. P.D This is the horizontal distance in mm from one pupil to the other. You can measure this by looking in a mirror and holding a ruler across your forehead just above the eyes. Scratch resistant coating This is a hard coating applied to the lenses to help prevent scratching AR coating This is an anti -reflective coating applied to the lenses to cut down surface glare, it is especially good for driving and computer work. Photochromic This is the name given to lenses that are clear but will darken outside in sunlight 1.6 high index This is recommended for rimless and semi rimless frames because of its resilience. It is also recommended for higher prescription above 2.00 because it is thinner and lighter. 1.67 high index This is recommended for prescription over 4.00 as it is thinner and lighter.
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