Axis - Indicates the placement in degrees of the astigmatic lens.

Anti-Reflective coating - Anti-reflective coatings improve the quality and the value of your lenses. An anti-reflective coating reduces disturbing reflections. It makes your lenses more attractive. And you will experience the most precise, crisp and clear natural vision in a brilliance that is not possible with uncoated lenses.

Bifocal - Corrective eyewear lenses containing regions with two distinct optical powers. Bifocals are commonly prescribed to people with presbyopia who also require a correction for myopia, hypermetropia, and/or astigmatism.

Color-Coated Lenses - Lenses that have a color coating applied to the outside of the lens.

Cylinder - An indicator of astigmatism on your prescription. If there is no cylinder value on your prescription, you do not have astigmatism.

DriveWear - A type of Polarized Transition Lens that transitions behind the windshield of a car. This type of lens is specifically for driving. The lens shade will vary depending on exterior lighting conditions, but never turn completely clear.

Eye size - The horizontal measurement of the lens on any frame at its widest part. This measurement is measured in millimeters.

Frame measurements - Most prescription frames will have your exact measurements engraved on the temples (arm pieces) or behind the nose bridge area.

Hi Index Glass Lenses - Available in a wide range of refractive indexes to provide the ultimate in thin, optically superior glass lenses. 1.6 high index lenses can be finished to a 1.5mm center in minus prescriptions and still meet United States FDA impact resistance standards. These high quality lenses are also available in 1.7, 1.8 and 1.9 indexes outside the United States.

Nose pad- The pads mounted to eyewear on either side of the nose that help support the frames.

Progressive lenses - These are no-line bifocals. There is no discernable line between the regions of optical power on the corrective lens with progressive lenses.

Polycarbonate - Polycarbonate lenses are the most impact resistant material. They are lightweight, have built in UV protection, and recommended for children, sports, as well as rimless frames. Originally used primarily for industrial safety glasses, they are now used for children, sports wearers, or anyone requesting greater impact resistance in their lenses.

Polarized lenses - Polarized lenses possess a filter that reduces the amount of reflected light that enters the eye. This filter reduces reflected glare which is most noticable on snow, or concrete asphalt surfaces and inside your windshield.

RX - Short for prescription. So, RXable would mean that the eyeglass or sunglass frame can hold prescription lenses.

Scratch resistant coating - A coating that makes lenses less prone to scratching.

Sphere - A part of your prescription. The sphere number denotes the strength of the lens in diopters.

Standart Plastic CR-39 - Traditional plastic lenses are made from a hard resin .These plastic blanks can be ground into specific shapes to fit any lens frame. Plastic lenses are great for prescription sunglasses due to their tintability factor.

Transitions ® Lenses - Photochromic lenses that transition from clear to dark in the presence of ultraviolet light and block 100% of harmful UV rays. Innovative photochromic technologies have produced unparalleled lens performance in nearly every lens design and material, including shatter-resistant lenses, bifocals, trifocals, progressives, and standard and high index materials.

Trifocal - Corrective eyewear lenses containing regions with three distinct optical powers. The three standard regions are distance at the top, intermediate in the middle and reading towards the bottom of the lens.

UV Filter - A lens coating, either on or embedded in the lens, that filters UV radiation.

Pupillary Distance (PD) or Pupil Distance - The distance (measured in mm) between the center of the pupils of your eyes when looking far away in the distance. If the prescription lenses are not set at the same distance as the distance between your eyes, then an unwanted prism is induced which may cause eyestrain. In lower prescriptions, the amount of prism induced will be of no consequence and will not cause eyestrain.