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Spectacle lenses: explaining the jargon

Spectacle lenses: explaining the jargon

8336 FAQ Jargon Bingo (SPECS & LENSES)

  • Anti-reflection coatingOpen

    An anti-reflection coating on your spectacle lenses means that more of the light reaches your eye and less bounces off the lens. This can make your vision feel clearer, and it makes the lenses less visible, so others can see your eyes better.

  • AsphericOpen

    An aspheric lens is one where the curve varies across the surface of the lens so that the lens is thinner and flatter. This is helpful for people who are longsighted and gives them the chance to wear lenses that magnify their eyes less.

  • BifocalOpen

    Bifocal lenses have two parts, one for distance vision, the other for close up. There is a line dividing the two parts. The ‘segment’ for reading can come in a variety of shapes, all of which save you from needing to get reading specs out every time you want to look at something close up.

  • High indexOpen

    A high index lens is one that uses a material that allows the lens to be thinner and lighter than a conventional plastic or glass lens. The stronger your prescription, the thicker your lens, so high index lenses are great for people with high prescriptions.

  • PolarisedOpen

    Polarised lenses include a filter that blocks intense reflected light off water or a wet road.

  • PolycarbonateOpen

    Polycarbonate is a type of plastic. It is thinner and lighter than CR39, the most common plastic used in spectacle lenses, and it offers better impact resistance too. It is thinner than Trivex, but may offer slightly less sharp vision due to the way it is made.

  • Refractive indexOpen

    The refractive index of a lens material is a number that is a relative measure of how efficiently the material bends light. A lens with a higher refractive index will be thinner and lighter than one with a lower value. However lenses with higher refractive indices can have higher chromatic aberrations, which means you may notice some coloured fringes at the edge of your lenses. For most people, the brain can adapt and ignore these as you get used to the lenses.

  • Single visionOpen

    A single vision lens is focussed for distance or near vision.

  • TrivexOpen

    Trivex is a type of plastic. It is thinner and lighter than CR39, the most common plastic used in spectacle lenses, and it offers better impact resistance too. It is not quite as thin as polycarbonate, but may offer slightly sharper vision due to the way it is made.

  • VarifocalOpen

    Varifocal lenses allow you to see at distance, intermediate and near, all in one lens. They don’t have a line like bifocal lenses, and are good if you want to look at different distances without changing your specs.