Gone are the days when a person with poor eyesight could only count on plastic-framed glasses with thick glass and heavy lenses. Modern ophthalmology can offer a lot of different options on the topic: “Spectacle lenses”. And the frames today are produced in a variety of shapes and from a variety of materials.
A bit of history…
The first mention of glasses can be found in documents dating back to the 13th century AD. The material from which the first frame was made was tortoise shell. It happened in China 2 thousand years ago. Approximately 1000 AD. e. monks began to actively use a magnifying glass when copying manuscripts.
When books became available to the public (this is a period around the 15th century), glasses became more in demand. Frames, lenses - everything was far from perfect, and their design was somewhat different than now. Then the person either held the glasses in his hand, or put them on the bridge of his nose.
By the beginning of the 17th century, eyeglasses equipped with temples appeared in London. And the end of the 19th century was marked by the fact that high-quality spectacle lenses were invented in Germany. They were glass, and suchthe situation continued until 1940, when a new type of plastic was developed in Pittsburgh, which became a worthy competitor to glass - fragile and quite heavy.
Over the next 75 years, optics developed by leaps and bounds. Today, modern lenses are classified according to a mass of parameters and can help a person with any eye disease.
Materials for making lenses
As mentioned earlier, eyeglass lenses can be either glass (inorganic) or plastic (organic). Glass for the production of lenses has been used for a long time. This material has excellent optical qualities, effectively protects the eyes from UV radiation. Its (glass) surface is sufficiently resistant to scratches. However, glass lenses are much heavier and thicker than plastic lenses, and it is not always possible to install them in modern frames.
Polycarbonate eyeglass lenses are thinner and lighter than glass. In addition, they are shock-resistant, which makes it possible to safely wear such glasses to children and people involved in sports. This material has the ability to protect the eye from ultraviolet radiation.
Since 2000, another eyeglass lens material, Trivex, has appeared on the market.
Options for the optical influence of lenses
Lenses for glasses for vision (or rather, its correction) are spherical, astigmatic and afocal in their optical action.
People suffering from farsightedness or nearsightedness are best suited for spherical lenses. The name astigmatic speaks for itself. Their main area of application is the correction of astigmatism. Moreover, with simple astigmatism, cylindrical lenses are needed, and with complex or mixed astigmatism, toric lenses are needed.
Afocal lenses do not have any optical capabilities at all. These glasses can be worn either by people without any problems with visual perception, or by those who suffer from aniseikonia (the eye has a significant difference in the size of the perceived images). In this case, when making glasses, eiconic lenses will be required. If a person suffers from strabismus, glasses are made with afocal prismatic lenses.
Optical zones and their number
There can be several optical zones in a lens, so their number can be classified into categories such as monofocality and multifocality. Multifocal, in turn, can be divided into bifocal, trifocal and progressive lenses for glasses.
Monofocal have one focus and are used only when correction of a single distance is needed - near or far. The scope of these lenses is limited to the correction of astigmatism and poor accommodation (the ability of the eye to change focus due to the weakening or strengthening of the contraction of the ciliary muscle) associated with age.
When it is necessary to correct vision at several distances at once, they talk about multifocal lenses.
An example of their use is presbyopia, when a person cannot see fine print or small objects onclose distance. Glasses with multifocal lenses will save a person from having to take them off when moving his gaze from a close distance to a distance and vice versa.
Types of lens coatings
Eyeglass lenses, no matter what material they are made of, will not have ideal characteristics. Meanwhile, the application of various coatings makes it possible to significantly improve their quality and capabilities, ranging from increased resistance to damage and pollution to improved visual comfort. Consider the most commonly used and sought after lens coatings among consumers.
Photochromic - makes it possible to protect the eye from the aggressive effects of ultraviolet radiation due to its ability to change light transmission depending on the illumination. Polarized lenses are coated with a special film (filter) and allow only vertically polarized or non-polarized rays to pass through, so the eye will not suffer from glare from water, road or snow.
To reduce discomfort when light rays are reflected from the sclera, cornea or lens surface, an antireflective (anti-reflective, anti-reflective) coating is applied.
Hardening coating increases the resistance of the lens to scratches, and hydrophobic makes them smooth, does not allow water, dirt and dust to accumulate and makes it easier to care for glasses. For those who spend a lot of time in the sun, goggles with a UV-blocking lens coating will be useful.
For the manufacture of sunglasses, a mirror coating is used, whichapplied only to the outer surface of the lens and can be of different color shades. In addition to all of the above, color coatings are widely used, i.e. the color of the glasses lenses can be very different.
Difficulty choosing: glass or plastic?
Currently, glass "eyes" have practically no advantages over their polymer counterparts. Plastic spectacle lenses, whose price can fluctuate significantly depending on optical parameters and hardening coatings, lead (and already by a large margin) in the optics market.
However, when it comes to correcting a high degree of myopia (a big minus of 10.0 diopters or more), from an aesthetic point of view, mineral lenses will look better due to the fact that their edge will be thinner than that of plastic.
In addition, glass lenses for eyeglasses are traditionally used by manufacturers that produce eye protection products from the sun.
Refractive index: which one to choose?
The refractive index of lenses made from polymers ranges from 1.5 to 1.74. The thinner and stronger the lens, the higher its coefficient. It weighs less and costs more. When choosing the right one, it will be guided by a prescription from a doctor and a frame that is preferred.
Monofocal or progressive lenses for glasses with small diopters (from -2 to +2) can be with a refractive index in the range from 1.5 to 1.6. With average diopters (from -6 to -2 and+2 to +6), the optimal coefficient will be from 1.6 to 1.7. If the diopters are high enough, it is best to give preference to lenses with a refractive index greater than 1.7.
If the consumer opted for a frame made of plastic, then in it a thick lens with a small coefficient will not be as noticeable as in a frame on a fishing line or on screws. If the frame is screw, then a thin and strong lens is preferable, i.e. with a higher coefficient.
Replacement lenses for glasses
There are people who don't have any vision problems, but they still wear glasses to maintain their image. Interchangeable lenses of different colors and shades in them enable their owner to match the environment in which he is, to see perfectly in all weather conditions, in the daytime and in the dark. Gray lenses will protect your eyes on a sunny day, blue lenses will be in demand during partly cloudy conditions, transparent lenses are designed for cloudy weather, and yellow ones perfectly polarize light from street lamps in the evening.
Athletes also tend to prefer glasses with interchangeable lenses, which are easy to change in one motion, but are firmly fixed in place. The shape of these lenses is designed to fit snugly to the face, but at the same time provides excellent vision. The water-repellent coating is also an important element of such lenses, water does not accumulate on them, but flows down freely, leaving no streaks.
Price range
Eyeglass lenses price mayfluctuate a lot. Products are considered inexpensive, the cost of which ranges from 1290 to 1700 rubles, lenses of the middle price category will cost from 2700 to 9000 rubles and even more. The expensive ones include products with a cost of 12,000 to 26,000 rubles. Everything is purely individual. The price depends on the mass of indicators: material, color and design of the lens, shade of anti-glare, diameter and thinning of the lens, its coating. In general, the more financial opportunities a buyer has, the more elegant, advanced and at the same time comfortable lenses for his glasses he can afford.
