Unlike the choice of the frame, in which the aesthetics of the product can be sometimes more considered than technical characteristics, the choice of the ophthalmic lenses is determined by specific parameters; when you choose them, suggestion and guide of the optometrist are fundamental. Have a quality lens means be sure of a clear vision, without distortions and able to guarantee those characteristics over time. According to the colors characteristics, they are divided into 4 categories:
Category 0: white lenses or slightly colored and clear photo chromatic lenses, to use in indoor or with a cloudy sky.
Category 1: medium colored lenses or dark photo chromatic lenses, to use with tenuous solar brightness. Photo chromatic lenses
Category 2: slightly colored lenses; to use with medium solar brightness. Comfort drive lenses
Category 3: dark lenses; to use with solar brightness.
Category 4: very dark lenses; to use with strong solar brightness, at the beach and in the mountains. Not to use on the street, included driving vehicles.
Main treatments for ophthalmic lenses are:
Non-glare treatment: it is a superficial multilayer which eliminates all surface reflections and ghosting that interfere with vision. A good non-glare treatment also offers:
A better transparence of the lens, improving the aesthetical effect
A better definition of the image, because of the better contrast
An attenuation of ghosting and so a reduction of discomfort for the wearer
A better performance of the lens
Non-glare treatment is always to suggest, especially with medium and high strength lenses, for night driving and computer users.
Treatment for blue-light protection: blue light is naturally present in the light spectrum, devices as LCD and LED of smartphones, tablets, TV, PC, and low energy lamps artificially emit it. It has a short wave-length, between 380 and 520 nm, rich in energy and able to increase the melatonin production and to have effects on the cardiac cycle, which regulates the sleeping schedule. The blue light also improve the development of some eye pathologies: cataract, conjunctivitis, alteration of the lacrimal film, age-related macular degeneration. For this reason, the lenses of last generation are endowed with specific treatments for the protection from the blue light, which allow working under best conditions, offering comforting vision and natural perception of the colors, reducing the dazzle, improving the contrast and attenuating the fatigue of the eyes.
Hardening treatment: it is a useful superficial layer in the choice of lenses made of organic material (unbreakable), to give great resistance to the scratches. It increases in fact the resistance to the micro abrasions of the lenses in organic resin.
Water-repellent treatment: it is a superficial layer, which allows the lens not keeping the filth and water drops, making it less subject to fogging and dirtying.
There are specific ophthalmic lenses for every need:
Monofocals lenses have only a dioptric strength and compose a single focal point; they are generally fitted in a half frame or in a complete frame, and they give a correction for only a distance (near or far). They can be distinguished in:
Spherical: lens with a single strength (positive or negative) which permits vision with an only distance (near or far)
Astigmatics: lenses with two different strengths on opposite medians of the lens; they are also called torics. So they form two focal lines whose interval expresses the astigmatism of the lens.
Lenses with more zones with different strength; they can be divided in:
To depth of field or dynamics: they are lenses with the advantage to allow an ampler and flexible vision in comparison to the monofocal lenses, in order to favor dynamic activities developing from nearby and from average distance (from 40 to 150 cm, more or less). They are excellent for the office and the computer because they allow the proximal and intermediary distance reading without distortions of image, and they contribute to maintain a correct posture to the desk. The optometrist recommends them to people who does activities at close range (users of PC, artisans, illustrators, doctors, housewives, etc. ) because, contrary to monofocal lenses, they allow to simultaneously focus on objects at varying distances, even if not over 150 cm. They are comfortable at the first use and do not require adjustment periods; they reduce the eye fatigue during the proximal distance work, and they are the recommended solution in case of Computer Vision Syndrome.
Progressive: they are lenses which represent, for people with presbyopia, the best technical solution since they offer a perfect vision for all distances: the lens passes from a minimal to a maximal strength, without continuity solution. The lens represents a way of progression which permits the correction even for midterm distances. The result, beside a better aesthetical effect, is great, and can be traduced as possibility to focus on every distance with the same lens, avoiding the jump of image in multifocal lenses. A glimpse and a neatness that never interrupt in any point of the space. They can be made of different materials and, according to the vision needs, can have personalized geometries. They are available under request with non-glare treatment, in protective and fashion colors, with polarizing or photo chromatic treatment, to obtain the maximum visual benefit in any light condition. Modern constructive technics allow realizing products of very high technology, extremely customizable and adaptable to every frame. For people practicing particular sport activities, specific progressive lenses are predicted and realizable even for embracing frames.
Bifocals: they are lenses with two different focal strength zones; the most wide zone of the lens is used for a long distance vision, the minor one (so called lunetta, and put in the direction of the nose) is used for proximal vision. They permit to people with presbyopia a differentiated correction, for long and close distances.