Glossary

The Add Power is the part of the multifocal lens e.g. bifocal or progressive multifocal lens, that corrects for near vision.

Astigmatism is a common disorder in which one or more of the eye's refractive surfaces (i.e., the cornea, or the lens) is not symmetrical. Astigmatism causes a perceived image to become distorted or blurred.

An Autorefractor is a computerized screening device designed to detect abnormalities of vision (i.e., nearsightedness, farsightedness, astigmatism).

The Axis is the term used in correcting for astigmatism. The cylinder power determines how much correction and the axis determines where the correction goes.

Base Curve is the front curve on a lens.

Cataract is a condition characterized by clouding in the natural lens of the eye. The cause is usually unknown but can result from exposure to ultraviolet light, injury, heredity, disease and advancing age. Some medical treatments include surgical replacement of the natural lens with an artificial lens. Cataracts are usually treated on an out-patient basis.

A Computerized Visual Fields Test is used to detect deficiencies in central or peripheral vision.

The Cornea is the clear outer covering of the eye. Known as the window of the eye, it plays an important role in focusing images.

Cylinder Power is the term used for correcting for astigmatism – the amount determines the power, and the axis determines where the correction goes.

Demo Lenses are plastic lenses inserted into frames for display purposes only.

Depth Perception is the appearance of depth created when both eyes focus on the same plane simultaneously.

The Eyewire is the section of the frame enclosing each lens.

The Frame Width is the size of the frames from left side to right side. The Frame width should equal the width of the wearer's head.

Glaucoma is an eye disease characterized by an increase in pressure inside the eye capable of causing damage to the optic nerve. Left untreated, this condition can lead to blindness. Glaucoma is usually treated with eye drops and medications. Severe cases may require surgical correction.

Hyperopia is another word for farsightedness.

A Keratometer is an instrument used to measure the curvature of the cornea. This measurement enables the doctor to accurately fit contact lenses.

A Lens Blank is an unfinished lens which is then ground to fit a customer's prescription.

A Lensometer is an instrument used to measure the power of an individual's current prescription eyeglasses.

A Multifocal Lens is a lens with more than one optical center (i.e., a bifocal with two, a trifocal with three, a progressive with many).

Myopia is another word for Nearsightedness

An Ophthalmologist is a doctor specializing in the eye who is trained to examine, diagnose, treat and manage diseases of the visual system, including all types of surgical procedures. This requires completion of an undergraduate program at medical school and a minimum of three years in ophthalmology training.

An Ophthalmoloscope is a hand-held, lighted instrument that helps detect a wide range of systemic and vision problems by giving the doctor a close-up view of the retina and other important parts of the eye.

The Optical Center is the spot on the eyeglass lens where light passes through without bending (refracting). This point is normally placed in front of the pupil of your eye.

An Optician is a professional trained to fit and adjust eyewear based on the specifications provided by an optometrist or ophthalmologist. Training requirements vary by state.

An Optometrist is a primary health care professional who can diagnose, manage and treat conditions and diseases of the human eye and visual system, as required by state law.

Peripheral Vision is the area of vision lying just outside the line of sight to either side of the face. For activities such as driving and sports, it is important not to obstruct peripheral vision.

A Phoroptor is an instrument used by the doctor to determine the final lens prescription and alignment of the eye.

Photo Refractive Keratotomy (PRK surgery) is a non-invasive, laser surgical procedure reshaping the cornea, which is the major refractive surface of the eye, to correct a refractive error. The only approved process right now is for nearsightedness (myopia).

Polarized Lenses are tinted lenses specifically designed to reduce glare. Those who work or drive in bright conditions and those who play snow or water sports would benefit from polarized lenses.

Polycarbonate is a synthetic, light material used to create impact-resistant lenses.

Presbyopia is a condition given to "elder eyes" whereby the crystalline lenses in the eye lose elasticity and do not change shape as easily as they should. Presbyopia causes people to have increased difficulty with near vision and reading, and is corrected with multifocals.

Prescribed Prism is an effect produced by de-centering a lens so that the optical center is not in front of the wearer's pupils. Less than five percent of all eyeglass wearers receive this prescription.

Progressive Lenses are Multifocal lenses with no telltale lines

The Pupil in the eye is a round hole formed by the iris that regulates what light passes into the eye. Light must pass through the pupil to get to the retina.

Pupillary Distance is defined as the distance, in millimeters, from one pupil center to the other. PD measurement is used to ensure proper lens placement.

A Pupilometer is a machine which measures the precise pupillary distance.

A Refraction is an eye examinations conducted to determine appropriate eyewear prescriptions.

The Refractive Index (RI) is the ability of the lens to bend light. Materials that bend the most light have the highest refractive index.

The Retina is the part of the eye that picks up images and transmits them to the brain via the optic nerve.

The Seg Height is the distance from the lowest portion of the eyewire to the top horizontal line of the Seg.

The Segment of the eyeglass lenses is that part used for near vision bifocals. The surrounding larger portion of the lens is used for distance vision.

A Slit Lamp is a device is used to closely examine external parts of the eye to detect for degenerative changes in the cornea and is also useful in routine contact lens evaluation.

The Sphere Power is the first number in a prescription for corrective lenses which indicates the type and amount of correction.

Tonometry is a computerized measure of internal eye pressure-glaucoma screening. A tonometer detects glaucoma by measuring the internal pressure of the eye with a puff of air.

The Transition Zone is the area of progressive eyeglass lenses where the distance vision curve gradually changes into the near-vision curve.

Trifocals are eyeglass lenses having three areas of viewing, each with its own focal power. Usually, the upper portion is for distance viewing, the lower for near, and the middle for the distance in-between.

UV Protection is the degree to which a lens or its coating protects the wearer's eye from the sun's harmful rays.