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EN
Glosary: 
Title: 
A - ACCOMODATION, AMETROPIA, AMD
Description: 

ACCOMODATION

The ability of the eye to see objects clearly as distance varies. Physiologically, this causes, among other things, the shape of the crystalline lens to change, which in turn increases the eye’s power.

AMETROPIA

With the exception of presbyopia, which is linked to age, this term characterises all vision defects that prevent a clear image from being formed on the retina. Myopia, hyperopia and astigmatism are types of ametropia.

AMD

AMD (Age-related Macular Degeneration) is a medical condition in which the macula, the central part of the retina, deteriorates, leading to a loss of central vision while leaving peripheral and lateral vision intact. Persons affected begin to have trouble discerning colours and straight lines begin to appear distorted.

Title: 
B – BLINDNESS
Description: 

BLINDNESS

The condition of a person who is blind, which signifies the lack of all visual perception. However, since vision is defined according to visual acuity and visual field, one distinguishes legal blindness, the loss of fine central visual acuity only (reading and writing, for example), from total blindness, in which there is a complete lack of light perception. With macular degeneration, legal blindness is defined as visual acuity of 20/200 or less in the better eye, even though the peripheral field of vision is preserved.

Title: 
C - CATARACT, COATED SURFACE, COATINGS, CONCAVE SURFACE, CONVERGENCE, CONVEX SURFACE, CORNEA
Description: 

CATARACT

Clouding of the crystalline lens, requiring its removal and replacement, most often by an intraocular lens. It can be hereditary or caused by trauma.

COATED SURFACE

An optical lens surface that has been coated with one or more thin transparent layers in order to protect the lens and reduce reflections and ghost images.

COATINGS

Thin transparent layers that help improve: durability, visual performance, ease-of-cleaning, etc. Several types of coatings can be applied to corrective lenses after surfacing: anti-reflection, scratch-resistance, anti-static, smudge-resistance, polarisation and tints. Application techniques vary. 

CONCAVE SURFACE

Back surface of a lens (the closest to the eye).

CONVERGENCE

The innate ability of the eyes to simultaneously fix on the same point in near vision.

CONVEX SURFACE

Front surface of a lens.

CORNEA

The slightly protruding, spherically-shaped front part of the eye. It plays an important role optically; along with the crystalline lens, it focuses images on the retina.

Title: 
D - DESIGN SURFACE, DIGITAL SURFACING, DIOPTRE, DOUBLE SURFACE PROGRESSIVE LENS
Description: 

DESIGN OR OPTICAL SURFACE

Surface that reflects or refracts light. The optical surface gives the material its optical correction. A practically infinite number of optical surfaces exist: they can be single vision, bifocal or progressive, spherical or aspheric.

DIGITAL SURFACING

Digital surfacing is a major technological advancement used in the production of corrective lenses. Most new progressive lenses are now machined using this technique.

With digital surfacing, visual performance can be optimized at each point, for each correction, and therefore for each viewing direction.

Digital surfacing allows a unique lens to be produced for each individual. This eliminates the compromise of seeking a single progressive design capable of satisfying the largest number of wearers, but which wouldn’t be optimal for any single one of them. 

DIOPTRE

A unit of measurement of the optical power of an optical system.

DOUBLE SURFACE PROGRESSIVE LENS

In general, a single complex surface is calculated for progressive lenses, for either the front or back, with the other surface being spherical or toric. There is thus little freedom to optimize each point on the lens. Thanks to the double surface design, each point on the two surfaces is calculated so that all the prescription parameters coincide perfectly: sphere, cylinder, axis and addition. This allows for an unlimited number of optical combinations, thus offering an increased degree of freedom in lens optimization.

Title: 
E – ENGRAVINGS
Description: 

ENGRAVINGS

The permanent markings present on certain lenses that serve to identify products and/or materials and/or mark the positioning of a lens

Progressive lenses have semi-visible (and standardised) engravings that serve to identify the geometry, addition and material as well as mark the side, far- and near-sighted positions of the lens. 

Title: 
F - FINISH AND SEMI-FINISHED LENSES
Description: 

FINISHED AND SEMI-FINISHED LENSES

Prescription laboratories transform semi-finished lenses into finished lenses by surfacing, tinting, adding anti-reflective coatings, edging and mounting. The front surfaces of all semi-finished lenses are finished at the factory while the back surfaces are surfaced to custom specifications.

Title: 
G - GLASS LENSES, GLAUCOMA
Description: 

GLASS LENSES

Scratch- and abrasion-resistant, glass lenses can be photochromic; they are made from silica and an oxide mix melted at high temperature. They are heavy and can break, but they have the advantage of being scratch-resistant.

GLAUCOMA

An increase in intraocular pressure which, if not treated, can lead to permanent damage to the optical nerve and retina as well as visual field impairment, namely diminished visual performance along with possible headaches and ocular pain.

Title: 
I - INTERMEDIATE LENSES
Description: 

INTERMEDIATE LENSES

Intermediate lenses are intended for patients with presbyopia; they are for near vision, but with more depth for intermediate vision.

Title: 
M – MYOPIA
Description: 

MYOPIA

Myopia is an ametropia caused by excess power or length of the eye. Since the image forms in front of the retina, myopes have poor distance vision, but can see objects close up.

Title: 
O - OPHTHALMOLOGIST, OPTIC NERVE, OPTICAL ABERRATION, OPTICIAN, OPTOMETRIST
Description: 

OPHTHALMOLOGIST

Doctor specialising in the treatment of diseases of the eye and the correction of visual defects. Ophthalmologists may also perform corrective surgery.

OPTIC NERVE 

Cylindrical cord, 5 mm in diameter and 35 to 55 mm in length, that connects the retina of each eye to the brain, to which images are transmitted via nerve impulses.

OPTICAL ABERRATION

The image reproduced by a lens or optical system is not constant – it varies depending on the portion of the lens through which the light ray enters as well as the ray’s angle.

When images are not formed by an optical system, light rays issuing from an object point do not form a perfect image point. All progressive lenses have these undesirable variations along the lateral portions of the lens.

Main types of aberrations: Loss of power, oblique astigmatism, prismatic effect, chromatic aberration and coma.

OPTICIAN

A specialized practitioner who fits glasses to wearers based on their prescription and needs.

OPTOMETRIST

An eye care professional who gives refraction exams in most English-speaking countries; optometrists do not deal with pathologies or perform surgery.

Title: 
P - PLASTIC LENSES, PHOTOCHROMIC LENSES, POLARISED LENSES, PRESBYOPIA, PRESCRIPTION LABORATORY, PRISMATIC EFFECT, PROGRESSION LENGTH, PROGRESSIVE LENSES, PUPIL, PUPILLARY DISTANCE
Description: 

PLASTIC LENSES

Manufactured using a “polymerised” resin base, plastic lenses are of very high optical quality. Twice as light as glass lenses, they are shock resistant and can be tinted and photochromic. However, they are more prone to scratching and must be coated.

PHOTOCHROMIC LENSES

Photochromic lenses react to UV intensity. They darken outdoors and lighten indoors, automatically adapting to changing light conditions. In general, they darken faster than they lighten. These lenses are also temperature sensitive, meaning they become darker at low temperatures.

POLARISED LENSES

Polarised lenses eliminate reflections from glassy surfaces (glass, water, snow, ice, etc), thus protecting the wearer from dazzling glare. They absorb horizontally polarised light (such as light reflected by a flat surface like the sea or snow) that our eyes cannot filter and which creates a hazy look.

PRESBYOPIA

Condition affecting vision due to the aging of the crystalline lens, which loses elasticity. This loss in elasticity reduces the lens’ ability to change shape, making it progressively harder to see objects close up. Presbyopia affects everyone after the age of 40.

PRESCRIPTION LABORATORY

Production units where semi-finished lenses are transformed into finished lenses meeting the characteristics specified in the order. This “made-to-order” work meets the needs of a vast number of optical combinations, particularly presbyopia. Laboratories carry out lens surfacing (grinding and polishing) and apply coatings (tinting, scratch protection, anti-reflection, smudge resistance, etc).

PRISMATIC EFFECT

Deviation of any light ray not passing through the optical centre. In lenses, any light ray that doesn’t pass through the optical centre deviates to a degree that varies depending on the distance from the incident light ray to the optical axis. 

PROGRESSION LENGTH

For progressive lenses, the distance at which the desired change in power is obtained. Distance representing 85% of the addition of a progressive lens. 

PROGRESSIVE LENSES

Lenses meant to correct presbyopia, the power varies in a continuous manner from the upper part (for distant vision) to the lower part (for near vision) of the lens without any break in the optical surface.

PUPIL

An aperture at the centre of the iris that allows light rays to enter the eye. Its diameter varies depending on brightness.

PUPILLARY DISTANCE

The distance between the centres of the pupils in each eye.

Title: 
R - REFRACTION, RETINA
Description: 

REFRACTION

The deflection of a light ray upon passing through a refractive surface. Term also used to designate the vision exam (to determine the power of corrective lenses). The phenomenon of refraction appears when light passes through the surface of a transparent medium (refractive surface). In eyeglass lenses, light is refracted twice (once at each surface).

RETINA

The light-sensitive membrane lining the inner surface of the eye on which images of objects are formed, and which transmits this information to the brain. This hypersensitive membrane plays a crucial role in perceiving light, colours, details, shapes and movement.

Title: 
S - SEMI-FINISHED, SINGLE VISION LENSES, SPHERICAL LENSES
Description: 

SEMI-FINISHED

In order to streamline costs and lead time in the industrial process, the front surface of a lens is finished beforehand, while its back surface is custom-finished at a later date.

Also known as a blank whose front surface (spherical, aspheric, multi-focal or progressive) is already finished and polished. The addition value is thus already incorporated into the semi-finished lens.

SINGLE VISION LENSES

A lens that has one single power across the entire surface of the lens.

SPHERICAL LENSES

In lens manufacturing, this term describes a lens that corrects one ametropia (myopia or hypermetropia). Rather, the back surface of the lens is spherical in shape as opposed to cylindrical. The opposite term is “toric lens”.

Title: 
V - VERTEX, VISUAL FATIGUE
Description: 

VERTEX

The distance between the eye and the back surface of the lens. This measure helps take into account the wearing conditions of the lens when they are mounted in the frame. 

VISUAL FATIGUE

Visual fatigue is characterised by eye strain, blurred vision and headaches, most often at the end of the day.

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