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Accommodation - The eyes ability to change focus from distant to near.
Add - The power required for near (reading) vision.
Ansisometropia - Very different refractive errors between the eyes.
Antinetropia - One eye myopic (nearsighted) and one eye hyperopic (farsighted).
Anti-Reflective (AR) Coating - A coating that is applied to both surfaces of the lens in layers to reduce reflections. This coating allows more light to be used by your eye for better vision. AR eliminates glare, increases light transmissions, reduces eyestrain, increases night vision and provides clearer cosmetically appealing lenses. A clear lens without AR only allows around 90% of the light to pass through to the eye-this is why AR helps you to see better.
Astigmatism - A condition in which the surface of the cornea is not spherical causing a blurred image to be received at the retina. This is reflected on a prescription as a cylinder (cyl) correction.
Axis - An imaginary line at right angles to the surface of a lens, which passes through the optical center. Also, the meridian of zero power in a cylinder lens, perpendicular to the meridian containing the maximum cylinder power.
Base Curve - The surface curve of an ophthalmic lens that becomes the base from which the remaining curves are measured. This is a measurement in diopters.
Bifocal - A lens with two powers; distance and near.
Binocular Vision - The blending of the separate images seen by each eye into a single image. Binocular vision allows images to be seen with depth. Pertains to both eyes.
Compound Lens - An ophthalmic lens that contains both a spherical and cylindrical refractive power.
Convex Lens - A spectacle lens that is thicker in the center and thinner on the edges. A convex or plus lens adds optical power to incoming light rays and is used for the correction of hyperopia (farsightedness). This is reflected on a prescription as + or positive power.
Decentration - The displacement of the lens optical center from the geometric center of the frame. A lens may be decentered in or out as to align the optical center with the center of the patient's pupils to reduce prismatic effect.
Diopter - A unit of measure of the refractive power of a lens.
Diplopia - Double vision.
Drill Mounted Frame - The lens are held in with brackets, plastic sleeves or screws that are drilled through the lens. This is the popular 'no frame' look.
Drivewear Lenses - A unique lens category because it is the first lens ever available that combines Transitions and Polarized technology together. This lens will change inside a car because it is activated by light instead of UV exposure, however this lens does not get clear inside.
Emmetropia - Normal eyesight.
Full Frame - Any eyeglass frame that has metal or plastic completely surrounding the lens.
Glass - The original lens material, it is rigid, shatters easily. is heavier but is more scratch resistant than other lens materials.
Hi-Index Lenses - Thinner lens materials with inherent UV protection. Cosmetically more attractive for prescriptions over + or - 2.00.
Hyperopia - Farsightedness; the ability to see objects in the distance clearly but not objects up close. May be corrected with eyeglasses. This is reflected on a prescription as a plus or positive power(+).
Lens Bevel - The edge of a lens shaped like a V. The bevel is manufactured to hold the lens in place inside a full frame.
Lens Power - The power of a lens measured in diopters.
Metal Frame - There are numerous 'metals' that eyeglass frames are made out of including stainless steel, titanium, nickel, aluminum, monel and sometimes a combination of several metals.
Monocular - Pertaining to one eye.
Myopia - Nearsightedness; the ability to see objects up close clearly but not objects in the distance. May be corrected with eyeglasses. This is reflected on a prescription as a minus or negative power (-).
Near Vision - Usually from about 11 inches to within arms reach.
Normal Vision - When vision is clear while seeing in both distance and near. The eye is able to focus images clearly on to the retina.
O.D. - Right Eye.
O.S. - Left eye; Latin meaning oculus sinister.
O.U. - Both eyes; latin meaning oculus uterque.
Ophthalmologist - A physician who specializes in the treatment of eye diseases, conditions and eyesight correction. An ophthalmologist is licensed to practice medical and surgical eye care.
Optician - An eyecare professional trained to design and adapt eyewear prescriptions for the specific wearer.
Optometrist - An eye physician that conducts refractive examinations and assesses overall eye health
Peripheal Vision - The ability to see objects and movement outside the direct line of vision.
Photochromic Lenses - Lenses that have the ability to change from clear (indoors) to dark (outside) with exposure to UV light. These lenses do not change inside a car. Blocks 100% UV light. This products is sold under trade names-Transitions, Instashades, LifeRX, Sunsensors
Plano - A lens without a refractive power.
Plastic Frames - There are numerous types of plastic used to make eyeglass frames including zyl (zylonite), cellulose proprionate, carbon, nylon cellulose propionate, Kevlar® and optyl. 50% lighter weight than glass lenses.
Polarized Lens - These lenses eliminate glare by absorbing sunlight and filtering only useful light to the eye. 98% absorption of UV light.
Polished Edges - This is a process that makes the lens edges clear rather than opaque.
Polycarbonate Lenses - Impact resistant, lighter weight than plastic, 99% UV absorption, and the recommended lens material for children's and sports eyeglasses.
Presbyopia - The gradual loss of the eyes ability to change focus from distance to near vision; the loss of accommodation. This condition is generally associated around the age of 40 for most people.
Progressive - Lenses with varying optical powers that progress from the upper part of the lens to the lower part with no lines that provide more natural vision.
Pupillary Distance - The distance between the center of one pupil to the other. Used for the proper positioning of eyeglasses.
Refraction - A test to determine a prescription to correct myopia, hyperopia, astigmatism and presbyopia.
Scratch Resistant Coating - A hard coating that is applied to the surface of the lens. This product helps reduce scratching but does not guarantee that the lens cannot be scratched.
Segment - The insert portion of a bifocal or trifocal lens that contains the plus power for near (reading) vision.
Semi-Rimless Frame - A frame that can be either metal or plastic that does not completely surround the lens. Generally the lens is held in at the bottom of the frame with a monofilament line giving the appearance of less frame.
Single Vision - The power of the lens is the same throughout the entire lens.
Tinting - A color that is applied to lenses with a dye that is absorbed into a layer on the lenses. Most colors are available for a tint. Some lens products cannot be tinted.
Trifocal - A lens with three powers; distance, intermediate and near.
Ultra Violet Light (UV) - Harmful radiation that is present all of the time, even on cloudy days.