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Eyeglasses.

Eyeglasses, before the invention of contact lenses, were tools needed to correct vision defects of various kinds. Wikipedia defines them as such "common use of a prosthesis composed of a frame and two lenses designed to correct defects of vision due to refractive defects or deficiencies in eye function."
In some cases, glasses are still inevitable , but that does not matter since, especially in recent years have become much more of a "prosthesis".
fashion, design, technology have introduced new forms, colors and materials revolutionized the industry and today glasses can be considered as a full real accessory of clothing. The variety of models, moreover, is so vast that anyone can easily find the eyewear fits your face, almost always adding something more "interesting" to the person, and that is why many prefer rather than be seen with glasses without it, and you may even find extreme cases where someone is wearing them without defects in the eyes, often in the world of VIPs.

FRAMES FOR EYEGLASSES

The materials they are made frames for eyeglasses and sunglasses are numerous.
We must always keep in mind though that the choice of the frame, even if the appearance, and then the blend of form, materials and colors with the physiognomy of the face, and the taste of those who must wear, is of fundamental importance in order to obtain results highly satisfactory from every point of view, consideration should also purely technical factors, such as construction materials of the frames, divided into:
Plastics, the most common plastic used for eyeglass frames is cellulose acetate, a material that offers a lot of very valuable opportunity to work with its strength and elasticity, and that can take infinite shades of color, characteristic for which the designers can give free rein to their imagination in the design of the frames. Other plastics can be used propionate, the Optyl, nylon etc..
Metal: In most cases, the metals used in the creation of frames are nickel silver, monel and the blank. In the last few years, however, the use of steel, titanium and their alloys has increased due to the important qualities of strength and light weight (especially titanium) which allow to obtain very thin and almost invisible frames. Titanium is more hypoallergenic and non-corrosive.
Rimless is called rimless, more commonly known as glasses "per day", the mount consists of a nasal bridge and two support rods with its hinges. These mechanisms are fixed with screws or pins to the lens through holes or joints that are molded on the lens. Temples and bridge are made ​​of plastic or metal (typically titanium).
Nylor is a type of eyeglass frames characterized from the top (ciliary) metal or plastic and the bottom with a thin nylon line that is positioned within which is a groove cut into the bottom edge of the lens. Very aesthetically beautiful nylor frames are only suitable in cases in which they are made of more resistant lenses.

TIPS FOR THE USE OF PRESCRIPTION GLASSES

Hygiene
"If your glasses are not cleaned properly, may be formed in time deposits which are the ideal breeding ground, a "glue" for the development of colonies of microorganisms such as fungi and bacteria, which multiply rapidly and therefore can cause infections eye.
There is a flora of fungi and bacteria that normally live in the eye healthy. The pathogenic microorganisms that grow in glasses or contact lens dirty, spread by air and can come in contact with the cornea to cause keratitis."(Wikipedia).
To keep the lenses in optimal conditions, it requires careful and thorough daily cleaning. We suggest using a spray product or wash them under running water with soap, then having to wipe them carefully with a soft cloth, making sure first that there are grains of dust and sand that can scratch.
Use
Never place the glasses upside down: no scratched surfaces may allow a more clear vision.
Once removed his glasses, put them back into the case always.
Avoid spray or squirt of chemical solvents that could cause the lens surface opacification.
Avoid exposure glasses to strong direct heat or steam jets (for example, never leave the glasses on the dashboard in the sun for a long time).
If possible, wear safety glasses and remove holding each arm with both hands. In this way, you will safeguard the symmetry of the frame.
Submit to periodic testing glasses: tightening the screws on rings and rods of the frame prevents leakage of the lenses.
In case of breakage, immediately replace the rubber pads and terminals.

LENS FOR EYEGLASSES

  • Progressive lenses

    In the ophthalmic industry, the more it can medium that to make the vision of the sighted close to that of non-sightedness is the progressive lens. In these brief notes describe the essential features of these lenses, an overview of the subjects more or less fit for their proper use.
    For near vision means that which takes place between 5 and 25 cm. : For this commitment our visual system must exert accommodation. it is evident that increasing age, and then of presbyopia, only these possibilities and is therefore necessary, with an ophthalmic lens, as modification of the lens can no longer give.

  • Features of progressive lenses

    The progressive lenses have two functional areas, one for distance vision (over 5 meters) and one for close (40-33 cm), these two pieces of glass are joined by an industry transition called channel of progression, where the power of the lens increases from top to bottom to get to the value of the power to close. This part of the lens is used for intermediate distance vision that is 40 cm. 5 meters.
    These lenses, compared to other optical solutions (single-vision lenses, bifocal, trifocal), then present those portions of the lens to allow clear vision at all distances, in addition to this honor, and other optical in nature, do not have the ugly dividing line present in bifocals and trifocals.
    Like everything else in this world, along with numerous advantages, do have certain conditions attached to what are called non-functional areas, ie areas peripheral to the channel of progression, in which the quality of vision is not perfect because of aberrations.
    We must point out that many restrictions are being increasingly solution and you're trying to do to be able to make the progressive lens, easy to use. And there is no doubt, however, that all problems can not be solved, much will still depend on proper patient selection, a proper mounting and centering of the lenses, as well as accurate information of what are the important steps for the achievement of adaptation and the correct use of lenses.

  • Indications of progressive lenses

    There are many situations in which the use of progressive lenses is not listed, or otherwise require special attention and long periods of adaptation.
    The less favorable situations are:

    • high astigmatism, especially if oblique.

    • disturbances (labyrinthitis, vertigo, hypertension and hypotension).

    • need for a wide field of view, both in the area near that far.

    • adaptation to the use of bifocal or trifocal.

    • ametropia not suitable for physiological and psychological reasons.

    • individuals with astigmatism different distance than near.

    • ametropia with physical disabilities who can not control the posture.

    • correction significant differences between the two eyes.

    • people who not well adapted to changes in prescription, or even the shape of the glasses.

    • Different addition in the two eyes.

    Should be emphasized that the adjustment period is about 10/15 days, during this period should govern themselves according to the instructions of the professional; however, some guiding rules for use of such lenses can be:

    • turning your head instead of eyes to look at objects sideways.

    • avoid tilt his head back to the remote viewing and not to lower his head for near vision.

    • get used to reading, to turn his eyes down most of the natural order, in order to pass the channel of progression, and this situation is unavoidable limitation of progressive lenses.

    • tolerated in the early days, a feeling of spatial disorientation. This problem will be felt less and less with each passing day to withdraw, in the worst hypothesis, in a few weeks.

    Ideal candidates for this type of lens are:

    • the young sighted that complains the first problems for the next vision.

    • short-sighted not high, not used to remove his glasses for near vision.

    • aphakia corrected with contact lenses or the pseudo phakic.

    • subjects for aesthetic reasons that do not accept the bifocal.

    • people with visual needs for medium distances (50/90 cm).

    The success rate obtained with the use of these lenses has been gaining increasing over the years to the point that you can consider this a reality now indispensable visual aid for sighted people who use it.
    It begs the question whether, from a technical standpoint, something else can be done to make them easier to use. The answer is yes, the technological development has allowed not only to optimize the front surface of the lens (the surface progressive), but also the rear. Reality progressive lenses are also made with photochromic materials or polycarbonate.
    In the near future will certainly be the lens that is optimized bearer to bearer, ie a personalized lens. Present is, however, the optimization of a variety of electronic systems for the detection parameters required for proper assembly, the reliability of computerized amount processing of lenses themselves and their centering, however, this can never be absolute need a wide knowledge of these lenses, is proposed by the professional to choose the most appropriate for that installation to its bearer.

  • BIFOCALS LENSES

    The bifocal lenses are the ideal solution to keep both a clear vision from near and far. In fact, bifocals have the advantage of focusing on distant objects, which is nearby.
    Although bifocals have this advantage over the single-vision lenses, they have some limitations.
    One of the main disadvantages of using bifocal lenses and the line of demarcation that separates perception from near and far. This is a problem because it creates a discontinuity when passing from the perception from a distance than up close.
    Another disadvantage of bifocals is the optical phenomenon known as 'jump' that occurs when you move your eyes from the section 'from a distance' of the lens, through the demarcation at 'close'. This causes distorted images, or stationed.
    Another limitation of bifocals and the inability, in most cases, to see objects at intermediate distance as your computer monitor. As you can understand, while distant objects are clear intermediate computer vision may remain blurred. In this case, the only way to focus on the computer screen is to use bifocal lenses and the section head closer to the monitor. Constantly move the head becomes very uncomfortable. Especially if the work is done on the computer for an extended period of time.
    The inability to focus on the intermediate vision is the main complaint of most of those who use bifocals. And as a result prompted a different type of multifocal lenses.

  • ANTI-GLARE COATING

    The anti-reflective coating is made on a lens in order to reduce the disturbing images that are formed by reflection from its surfaces. Images can be generated by radiation from sources located:

    • Behind the lens and reflected from the rear surface.

    • Behind the lens after being refracted by the back surface, reflected from the front and further refracted by the back surface, reach the eye.

    • front of the lens, obtained by refraction on the front surface, two reflections (the first on the back surface and then on the front) and another on the back surface refraction. Despite their low-intensity reflections are the most annoying.

    • front of the lens, after the crossing, are reflected on the cornea and, after further reflection on the rear surface of the lens come back to eye-level, their intensity is much reduced.

    • front of the lens, in this case the light rays, after the crossing, are reflected on the cornea and, after a first refractive index on the back surface, are reflected on the front, arriving in the eye after refractive further on the back surface. This image similar to the previous one, has a low intensity.

    The anti-reflective coating, although multi-layer, can not completely eliminate all wavelengths reflected from the lens and it is for this reason that lenses treated have, however, a residual stain. Since the intensity of the reflections increases with increasing refractive index of the anti-reflective coating lens material becomes important in order to obtain:

    • increase in brightness.

    • better definition of the image to increase contrast.

    • attenuation of reflected ghost images.

    • greater continuity in the level of performance as the perceptive activity is less disturbed by the ghost images.

    • reducing blemishes associated with reflections generated by the front surface of the lens.

    An anti-reflective coating is always advised, particularly in the following cases:

    • lenses in medium and high power are reduced because the concentric rings due to the reflection device.

    • for night driving as the user is not bothered by lights, street lamps and neon signs.

    • in anisometropia because it reduces the difference in appearance between the two lenses.

    • for contact lens wearers with high prism powers.

    • for VDU operators.

  • PHOTOCHROMIC AND ANTI UV

    Photochromic lenses, or with anti-UV rays, which contain active photochromic pigment - or darkens - the lens exposure to ultraviolet (UV) radiation from sunlight. When the UV light diminishes, the lenses fade back to clear. To changing light conditions outdoors, the level of darkness adjusts, creating the right level of tint and allowing just the right amount of light reaching the eye. This allows the photochromic lenses to help protect your eyes from visible light, reducing glare, reducing eye strain and allowing you to distinguish contrast more easily.
    For the light you can not see ultraviolet light, photochromic lenses help protect your eyes in order to preserve healthy sight in the long term. It is important to remember that, whatever the appearance and intensity of light, photochromic lenses are always blocking 100% of harmful UVA and UVB rays. In other words, the photochromic lenses provide automatic protection from UV rays in any environment, continually protecting your eyes from the invisible light and offering a vision of good and comfortable in the visible.
    Fotocromatche lenses begin to darken when exposed to UV light. The greater the intensity of UV light, the darker the lenses become. When the UV rays are no longer present, the lenses immediately begin to return to their clear state. Most people who wear them report that the adjustment happens so quickly and smoothly, they do not realize it. But they remain aware of the visual comfort the lenses continue to provide in any light condition.
    The reverb can be described as a "very bright" due to the presence of visible light in excess. Glare can be distracting and even dangerous and can occur day and night in different ways.
    Glare can cause discomfort to the eyes that causes fatigue. In extreme cases, glare can also cause temporary blindness.
    Must consider four types of glare:

    • Distracting reverb

      Distracting glare can be caused by the lights of cars or urban night lighting. It can also be simply a reflected light on the front of the lens that does not allow others to see clearly for yourself. Likewise, it may also be due to the reflection of light on the back or inside of your lenses, you'll see the reflection of your eyes or distracting objects behind you in the visual field in front of you. Consequently this type of glare can cause eye fatigue, discomfort and distraction.

    • Annoying reverb

      Glare can be caused by the normal conditions of sunlight each day. According to the individual sensitivity to light, this reflex can be annoying regardless of weather or time of day. May be present at every level of intensity of light, or when you move from one light condition to another. The annoying glare often causes discomfort and eyestrain.

    • Disabling reverb

      This type of reverb comes from a strong light and excessive and can occur when you are directly in front of the sun. The disability glare can block vision because the intense light can cause a significantly reduced contrast of the image on the retina. The latent effects can last beyond the period of exposure.

    • Reverb or blinding glare

      Is caused by light reflected from smooth and shiny surfaces such as water, sand or snow. It can be strong enough to block vision. The reflected light is polarized and requires polarized lenses to be reduced in an optimal manner.

  • MATERIALS FOR THE CONSTRUCTION OF LENSES

    Materials used to construct the ophthalmic lenses (spectacle lenses) can be divided broadly in mineral glass lenses, lenses in organic material and polycarbonate lenses.
    The mineral glass lens are divided in turn into:

    • 1.5 crown glass lenses

      Crown glass lens is 1.5, among those in mineral glass, the most commonly used for myopia and hyperopia compensation read. This material has refractive index of 1.523 and specific gravity 2.61, has good optical properties, such as the low chromatic dispersion (Abbe number 58.8), the 'high transparency can be further enhanced with the' application of a 2 anti-reflective coating on surfaces, in order to minimize reflections. It 'available tinted or photochromic, it's the fragility of the glass.

    • 1.6 crown glass lenses

      1.6 crown glass lenses are used for myopia and hyperopia compensation for light to medium. This material has refractive index of 1.60 specific gravity of 2.63 and Abbe number of 41.5, has the same characteristics as the 1.5 except the crown 'index of refraction slightly higher, it follows that other things being equal , the thickness will be slightly lower, and the chromatic dispersion is slightly higher as inversely proportional to the Abbe number.

    • Lenses Titanium 1.7

      Titanium 1.7 lenses are more suitable for medium myopia, and high speeds. 'S index of refraction is equal to 1.70 and the specific gravity is 3.21. Compared with crown glass, has a higher chromatic dispersion (Abbe Number 35 or 40), more reflection on surfaces and greater fragility, in addition to the weight considerably higher. Like all glass lenses, including glass, titanium, and colors. In conclusion, the 'only value is the titanium lens' high index and hence the reduced thickness of the edge. On this type of anti-reflective lenses is recommended.

    • Lenses lanthanum 1.8 and 1.9

      Lenses lanthanum lanthanum 1.8 and 1.9 lenses, the lenses have properties similar to titanium 1.7, with the 'stress of all the defects of titanium, and the' only advantage of greater reduction in thickness due to the higher refractive index (1.80 to 1.8 and 1.89 for lanthanum lanthanum 1.9). In conclusion, lanthanum lenses are shown in high and very high myopia, or in all cases in which the subject sees it as an absolute priority the reduction of thickness.

    Organic material lenses

    The organic material lenses are available in a variety of refractive indices ranging from '1.50 of the classic organic material called CR39, all' and to 1.67 '1.74 of the relatively new organic materials with which we obtain lenses as thin as or more than titanium, with the great advantage dell'infrangibilità and a significant reduction in weight. The downside of organic materials in general, is given by the low resistance to abbrasioni, defect, however, was mitigated by the new hardening treatments applied to the surfaces, even with the extra multi-coated and another treatment that makes cleaning easier. However, it is advisable to pay close attention to the cleaning of organic lenses, completely avoiding rubbing the surfaces until they were thoroughly washed in running water to remove any particles abbrasive.
    The size and shape of the rim of the frame used is another important factor in determining the thickness of the lens and then the final result. In the choice of the frame, unless it is very mild corrections in terms of dioptric, do not take into account only the aesthetic factor and trendy, but when the values ​​of nearsightedness, farsightedness or astigmatism exceed 2 dioptres, is appropriate choice of frames sizes much smaller the greater the degree of visual defect and the smaller the interpupillary distance of the subject, bearing in mind that if on the one hand, the small frame allows for thinner lenses, the field of view is inevitably reduced.
    As said about the thickness and weight of the lenses is not only for nearsightedness, farsightedness and also for 'any astigmatism, only that, but for simple myopia or myopic astigmatism associated with, the greater thickness is presented in the lens device, in the case of 'simple or hyperopia associated with hyperopic astigmatism, the greater the thickness at the center.
    The choice of a lens can be influenced by the type of activity, work or use that you intend to do with quell'occhiale.

    Polycarbonate lenses

    Born as polycarbonate plastic for the aerospace industry before being used with great success in the optical (lenses and protective sunscreens for sport) with the security it offers in terms of resistance to breakage and chipping.
    The polycarbonate lenses are also valued for their lightness and subtlety, with a refractive index of medium-high, the natural UV protection properties.
    Are confirmed as the best lenses for children and children, for athletes and for those who are exposed to heavy work or activities.

COMPUTER and eyeglasses

The widespread use of personal computers in the workplace and at home, bring more people to suffer from visual discomfort, headaches and feeling of fatigue due to hours spent in front of the monitor. To resolve this problem, much more common than one would think, you can use special glasses for use in display screen, which is equipped with special lenses for this use. Those who do not have visual defects, they should use anti-glare lenses with color degrading a specific shade of gray / blue with appropriate micro-diopter adequate working distance. Increasing contrast and eliminating the flicker effect of a typical monitor, can greatly reduce eyestrain For those who already have visual defects such as myopia, hyperopia, astigmatism and presbyopia, lenses can be made specific, by optimizing the near vision, even eliminate these problems. In particular for the correction of presbyopia can be made slow dynamics, as well as improving the reading on the monitor, allowing an optimal view at a radius ranging from 33 cm to over 1 meter, with a much wider field of view than normal "slow reading".