OPTICAL DEFINITIONS AND TERMS
Today, the glasses that you wear are very marked products resulting from the combination of several elements.
Here is a small glossary available to help you find your way around before your visit to 4380 bd Saint-Laurent …
Ametropia
This visual defect is due to a too long eye. As a result, the image of what you see is projected in front of the retina. Divergent or concave glass pushes this image back onto the retina. This glass is thicker on its edges than in the center.
Unlike myopia, this defect results from too short an eye; the image therefore forms behind the retina. A converging or convex lens then brings the image closer to the retina. This glass is thicker at the center than at the periphery.
If you have astigmatism, your eye shape is not perfectly round. It is indicated on your prescription by the axis of astigmatism. To compensate for it, you wear a so-called thoric glass. Most often, this visual defect is associated with another, myopia or hyperopia.
It’s not really a visual defect. Presbyopia results from a difficulty of accommodation associated with normal aging of lens tissue. This is why everyone becomes farsighted one day. In the early stages, presbyopia manifests itself as difficulty seeing up close. To correct it, you can initially make do with a near or mid-distance vision lens. But the best solution in the long term is to wear progressive lenses.
The glasses
Single vision lenses are also called single focus. They correct only one visible defect and have the same power over their entire surface. Divergent, they compensate for myopia; converge, they correct hyperopia.
Invented by Bernard Maitenaz d’Essilor in 1959, the progressive compensates, thanks to the variation in power on its surface, for defects in near vision, intermediate vision and far vision. So you only need a pair of glasses, which is both more practical and more aesthetic. Since 1959, considerable progress has been made and there are no longer any real problems of adaptation to this type of lens.
There are two types of glasses. Mineral glasses (glass!) Are now rare. They have the advantage of being more resistant to scratches and of high optical quality, but they are fragile and heavy. They are prohibited for children under 16. The most common organic glasses are made of plastic. We can talk to you about polycarbonate, CR39, Trivex, MR8: all are organic. Their advantages? Lightness, solidity. Disadvantage: they must be maintained with more care.
The index of a lens depends on its material: thus the CR39 has an index of 1.5, the polycarbonate of 1.6, etc. The advantage of a lens with a high index is that for the same correction you can have a thinner lens. Undoubted aesthetic advantage and comfort also since your equipment will be lighter.
In order not to damage your glasses, it is essential to take a hardened treatment thus increasing the resistance to scratches. Anti-glare eliminates stray reflections and improves the quality of your vision. Anti-fouling antireflection provides additional comfort: your lenses are easier to clean and stay clean longer. All these options certainly increase the price of glass but allow you to benefit from the best equipment.
These corrective lenses vary in color depending on the brightness. In summary, they are dark on the outside and stay light on the inside. The advantage: you have effective protection against glare and sunlight without even thinking about it. They exist for all fixes. Good to know: most corrective lenses currently sold provide 100% UV protection.
The principle of these lenses is to integrate into their development a certain number of results of additional measures taken by us: inclination of the frame on the face, lens-eye distance, natural reading distance, visual behavior (you move the frame instead. head or eyes), satisfaction with previous equipment. Some lens manufacturers have even developed devices to capture your eye. You get it, everything that is clean (including your lifestyle and your hobbies) allows you to design a truly tailor-made glass.
Optical terms
The image given by a glass has deformations on the sides: they are more or less large, depending on the power of the glass, and of different shapes depending on your visual defect. The quality of the glass lies in the attenuation of these distortions: the more elaborate your glass, the fewer areas of aberration you will have. It is in this context that we can talk to you about spherical (standard), aspherical (optically more sophisticated) or personalized lenses (with an area calculated point by point).
A cataract is formed when the lens of the eye, which is normally clear, becomes foggy and cloudy. The affected area can be extremely small or very large, causing appreciable vision loss.
It is an optic nerve damage characterized by high pressure inside the eye. This pressure is caused by difficulty in draining one of the fluids in the eye: the watery humor. When these channels no longer work as they should, due to a blockage or overproduction of aqueous humor, fluid builds up and creates pressure inside the eye. When it becomes severe, this pressure can damage the optic nerve and cause gradual and unrecoverable vision loss.
Macular degeneration is a multifactorial disease associated with age that gradually destroys the macula, which is responsible for seeing details. It is the leading cause of vision loss in people over the age of 60.
The first stage, called underlying diabetic or nonproliferative retinopathy, is characterized by the swelling of tiny blood vessels in the retina. It is not accompanied by any significant visual disturbance. The most advanced stage, proliferative retinopathy, is characterized by the presence of abnormal vessels on the surface of the retina, which take the form of roots. These new vessels, very fragile, swell and cause hemorrhages which lead to significant vision loss or blindness.
