Glossary
08-2008
Aberration - Optical system image defects; rays of light emanating from an object-point fail to form a
perfect image-point.
Accommodation - The eye’s ability to clearly see objects at close distances.
Addition - The optical power (of a lens) required for near vision, in addition to that required for far vision.
Amblyopia - Amblyopia, or lazy eye, is reduced visual acuity that cannot be improved by wearing eyeglasses.
AMD - Age-related macular degeneration, a disease that damages the macula, the central part of the retina, leading to a loss of central vision and leaving only the peripheral or lateral vision intact.
Ametropia - Eyesight disorders that prevent a clear image from forming on the retina (myopia, hyperopia, astigmatism).
Astigmatism - An irregularity in the curvature of the cornea, resulting in unequal blur in the two principle meridians.
Bifocal Lens - Lens with two points of focus, designed to relieve presbyopia. The lower part of the lens allows near vision; the rest of the lens is designed for far vision.
Cataract - Opacification of the crystalline lens. An extraction of the lens is usually replaced by an intra-ocular lens (implant).
Coatings - Applied to corrective lenses after surfacing to be scratch-resistant, anti-reflective, polarizing, color, antistatic, anti-smudge.
Contact Lenses – Small soft or rigid lenses floated on the tear film over the cornea to correct eyesight.
Convergence - Reflex that enables the eyes to focus on a single point in near vision.
Cornea - Transparent front part of the globe shaped like a slightly domed cap. It is the primary focusing structure with the lens.
Corrective Lenses -Corrects eyesight disorders and is a combination of material, optical surface and coatings.
Crystalline Lens - Transparent biconvex lens located behind the pupil; refracts light to focus images on the retina.
Diopter - Optical system with a focal distance of 1m. Refraction defects are measured in diopters (visual insufficiency).
Digital Surfacing - Precise surface cutting using single point turning; cutting height is controlled at all points on the lens.
Emmetropia - Clear and comfortable eyesight in both far and near vision. Emmetropia is the opposite of ametropia.
Fovea - Small depression in the central part of the macula measuring located close to the optical axis of the eye.
Glaucoma - Increase in intra-ocular pressure resulting, if left untreated, in an irreversible deterioration of the optical nerve and of the retina, as well as an alteration of the visual field, i.e. a reduction in visual performance, often accompanied by headaches and aching eyes.
Half-eye Lenses - Lens for near vision only shaped like the lower half of a normal lens.
Hyperopia - Far-sightedness, an eye that is too short and/or insufficiently powered. The image forms behind the retina, which explains why the hyperopic subject has better eyesight in far vision than in near vision. In cases of mild hyperopia, the subject sees
correctly in far vision by compensating the hyperopia through accommodation. In cases of severe hyperopia, the eye can no longer compensate in this way.
Intraocular Pressure - Fluid pressure exerted inside the eyeball (ocular globe), which keeps the wall taut.
Iris - Circular membrane that delimits the pupil. The iris acts as a diaphragm that contracts according to the intensity of light.
Macula - Central part of the retina. Composed uniquely of cone cells and enables precise vision.
Myopia - Near-sightedness, an eye that is too powerful or too long. The image forms in front of the retina; a person with myopia thus sees badly in far vision but well in near vision.
Ocular Globe - The eyeball, about 25mm in diameter when emmetropic.
Ophthalmologist – Physician, surgeon specialized in the treatment of eye diseases, conditions and eyesight correction.
Optical Correction - Combination of the curvatures of the front and rear surfaces of a lens, measured in diopters.
Optician - Eyecare professional, designs and adapts eyeglasses in accordance with measurements specific to each wearer.
Optometrist - Eyecare professional, conducts refractive examinations, fits contact lenses and assesses overall eye health.
Organic/Plastic Lenses - Organic lenses are made from a "polymerized" resin.
Photochromic – Variable tint lens that can darken or lighten depending on the presence of UV.
Polycarbonate – Lens material characterized by lightness, impact resistance, high refractive index, UV absorption.
Presbyopia - Eyesight disorder caused by the aging of the crystalline lens, which with time thickens and loses its suppleness. As the crystalline lens becomes more rigid, it changes shape less easily and the subject sees less and less well in near vision.
Prescription Laboratories - Transforms semi-finished lenses into finished lenses and then edges and glazes into frames.
Progressive Lenses - Corrects presbyopia by varying optical power progressively from an upper to lower part. No lines.
Pupil - Central opening of the iris through which rays of light enter the eye. The diameter depends on ambient light.
Refractive Index - Characterizes the way a transparent optical material bends or refracts light.
Retina - Light-sensitive membrane at the back of the eye on which object images are formed and which transmits information to the brain. This hypersensitive membrane plays an essential role in the perception of light, colors, details, shape and movement.
Semi-finished Lenses - The front surface is finished and the rear face is surfaced on demand.
Single Vision Lenses - Correct ametropia or presbyopia. The power is the same over the entire lens.
Strabismus - Eyesight disorder related to a defect in the parallelism of the visual axes. Early detection in children is vital in order to avoid any risk of amblyopia. There are three forms of strabismus.
Surfacing – The grinding and polishing of a lens surface.
Visual Acuity - Ability to discern the details of an object. A normal average eye an angle of one minute of arc (1/60th degree).
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