In school physics lessons we remember that light rays travel in a straight line. Any object in their path partially absorbs light and partially reflects it at the same angle at which it falls. The only exception is when light passes through a transparent object. At the boundary of two transparent media of different densities (for example, air and water or glass), light rays are refracted to a greater or lesser extent, and amazing optical effects arise, depending on the physical characteristics of the object through which the light passes.
This property of light allows you to control the course of rays, changing their direction or turning a diverging beam of rays into a converging one, and vice versa. In practice, this can be achieved using specially processed devices made of optically transparent homogeneous material, which are called lenses (lat. lens “lentils”). Looking at an object through lenses with different physical and chemical characteristics, we will see it upright or inverted, enlarged or reduced, clear or distorted.
The simplest lens is a carefully ground and polished piece of a highly transparent substance (glass, plastic, mineral), limited by two refractive surfaces, two spherical or flat and spherical (although there are lenses with more complex aspherical surfaces). Lenses whose middle is thicker than the edges are called converging (positive), diverging (negative) are called lenses whose edges are thicker than the middle. A positive lens has the ability to collect rays incident on it at one point located on the other side of it, at focus. A negative lens, on the contrary, deflects rays passing through it towards the edges.
The simplest rock crystal lens.
Although the scope of use of lenses in science and technology is very large, their main functions boil down to a few basic ones. This is the accumulation of thermal energy of light rays, visual approximation and magnification of small or distant objects, as well as vision correction because the lens of the eye by its nature is a lens with variable curvature of surfaces. People began to use some properties of lenses earlier, others later, nevertheless, these optical devices have been known to them since ancient times.
There are different opinions about when people learned to create fire using sunlight and polished pieces of transparent stone or glass with a convex surface. We can say for sure that this method was known in Ancient Greece in the middle of the 1st millennium BC. e., since it is described in Aristophanes’ play “The Clouds”. However, lenses made of rock crystal, quartz, precious and semi-precious stones found during excavations are much older. One of the most ancient lenses, the so-called god with glasses, was discovered during excavations of Uruk, an ancient city-state in Mesopotamia. The age of this lens is about 6 thousand years, but its purpose remains a mystery.
In Egypt during the IV-XIII dynasties (III-II millennium BC), crystal lenses were used for... models of eyes in statues. Optometric studies have shown that models are very close to the actual shape and optical qualities of the eye, and sometimes even show visual impairments such as astigmatism.
Alabaster “idols with eyes.” Tel Brak site, Syria. IV millennium BC e.
Unfortunately, over time, the secret of making such lenses was lost; the false eyes of statues began to be made of stone or faience. The “glass eyes” technique, although with less perfection, was also used by the ancient Greeks. For example, bronze statues of the 5th century were equipped with lenses. BC e., discovered in the sea off the coast of Calabria. But there were still many centuries left before the “official” discovery of the optical properties of the eye!
During excavations in Mesopotamia, Greece and Etruria, a considerable number of crystal lenses dating back to approximately the end of the 1st millennium BC were discovered. e. A study of their decoration showed that the lenses were used both for visual magnification and as decoration. Essentially, these were true magnifying glasses with a short focal length that increased the angle of view. In addition, miniature gems were found in Greece, connected by a frame with convex lenses; these gems would not be possible to produce without optical magnification of the working field. All this indicates that magnifying glasses began to be used long before the magnifying effect of lenses was recorded in scientific sources.
When exactly lenses began to be used for vision correction has not yet been established. There is an opinion, however, not supported by anything, that lenses discovered during excavations of ancient Troy were used precisely for this purpose. In the works of the Roman historian of the 1st century. Pliny the Elder mentions that Emperor Nero, who suffered from myopia, watched gladiatorial fights through a concave lens carved from emerald, this was a kind of prototype of glasses. Some historians, based on ancient engravings, believe that glasses were invented in China in the 7th-9th centuries, but whether they were optical or sunglasses is unknown.
An Arab scientist of the 9th century was the first to seriously study the eye as an optical system. Abu Ali al-Hasan, known in Europe as Al-Khazen. In his fundamental work, The Book of Optics, he relied on the research of a Roman physician of the 2nd century. Galena. Al-Hasan described in detail how an image of an object is created on the retina of the eye using the lens. However, the essence of myopia, farsightedness and other vision defects, in which the focus of the lens shifts relative to the retina, was finally clarified only in the 19th century, and before that, glasses were selected virtually at random until the desired effect was achieved.
Mysterious optics
On the Swedish island of Gotland, in a treasure buried about a thousand years ago by the Vikings, lenses of complex aspherical shape made of rock crystal were found. This form of lenses was theoretically calculated only in the 17th century. Rene Descartes. In his work, he indicated that these lenses would give an excellent image, but for a long time not a single optician could produce them. It remains a mystery who could have polished the lenses from the Viking treasure and for what purposes.
Seller of glasses. Engraving after a painting by Giovanni Stradano. XVI century
It is believed that glasses were invented in Italy at the end of the 13th century, their invention is attributed to the monk Alessandro Spina or another monk Salvino D'Armata. The first documentary evidence of the existence of glasses dates back to 1289, and their first image was discovered in the church of Treviso on fresco painted in 1352 by the monk Tommaso da Modena. Until the 16th century, glasses were used only for farsightedness, then glasses with concave lenses appeared for the nearsighted. Over time, the shape of the glasses changed, and the frame and arms appeared. In the 19th century, Benjamin Franklin invented bifocals lenses, which in the upper part are intended for distance work, and in the lower part for close-up work.
J.B. Chardin. Self-portrait with glasses. 1775
Jan van Eyck. Madonna and Child with Canon Joris van der Paele. Fragment. 1436
Photochromic lenses (“chameleons”) were created in 1964 by Corning specialists. These were glass lenses, the photochromic properties of which were given by salts of silver and copper. Polymer lenses with photochromic properties appeared in the early 1980s, but due to significant disadvantages, low darkening and lightening rates, as well as extraneous color shades, were not widely used. In 1990, Transition optical released more advanced plastic photochromic lenses, which gained enormous popularity.
Contact lenses are considered a relatively young invention, but Leonardo da Vinci worked on their device. Many scientists thought about how to put a lens directly on the eyeball, but only in 1888 did the Swiss ophthalmologist Adolf Fick describe the structure of a contact lens and begin experiments. Mass production of contact lenses was started in Germany by the famous optical company Carl Zeiss. The first samples were completely glass, quite large and heavy. In 1937, lenses made of polymethyl methacrylate appeared. In 1960, Czechoslovak scientists Otto Wichterle and Dragoslav Lim synthesized a new polymer material, HEMA, developed a method of rotational polymerization, and produced soft contact lenses. At the same time, hydrogel lenses were developed in the USA.
As for the magnifying power of single lenses, it soon became clear that it was limited, since increasing the convexity of the lens led to image distortion. But if you place two lenses in succession between the eye and the object (eyepiece and objective), the magnification will become much greater. Using the lens at the focal point, an actual image of the observed object is created, which is then magnified by the eyepiece, which acts as a magnifying glass. The invention of the microscope (from the Greek mikros “small” and skopeo “I look”) is associated with the names of the Dutch John Lippershey and the father and son Jansen (late 16th century). In 1624, Galileo Galilei created his compound microscope. The first microscopes provided magnification up to 500 times, while modern optical microscopes can achieve 2000 times magnification.
Simultaneously with the first microscopes, telescopes (or spyglasses) appeared (their invention is attributed to the Dutch Zacharias Jansen and Jacob Metius, although the first attempts to look at stars using lenses were made by Leonardo da Vinci). The first person to point a telescope into the sky, turning it into a telescope (from the Greek tele, “far”), was Galileo. The principle of operation of an optical telescope is the same as that of a microscope, the only difference is that the lens of the microscope gives an image of a nearby small body, and a telescope of a distant large body. However, since the end of the 17th century, telescopes have used a concave mirror as a lens.
Otto Wichterle in the laboratory.
Among other things, lenses are used in the field of photography, film, television and video, as well as for the projection of finished images. The lens of a camera and similar equipment is an optical system of several lenses, sometimes in combination with mirrors, which is designed to project an image onto a flat surface. The curvature of the objective lenses is calculated so that possible aberrations (distortions) are mutually compensated. Joseph Niepce, who created one of the first cameras in 1816, borrowed a lens for it from a microscope.
Since the second half of the last century, electronics with higher resolution have been used, along with optical systems, to observe various micro- and macro-objects. However, lenses are still used so widely that it would be quite difficult to list all their applications.
Camera by Joseph Niepce.
Refracting telescope at Lick Observatory. California, USA.
In 1508, Leonardo da Vince created a drawing depicting a glass sphere filled with water, with the help of which a person with poor eyesight could see better.
Glass shaped like an eye
130 years after this significant event, the French mathematician Rene Descartes proposed using a glass cylinder of water for the same purpose, attaching a magnifying glass to its end.
Another two hundred years later, in 1827, the English physicist and astronomer John Herschel first described a glass lens that follows the shape of the eye. And already in 1888, the German glassblower Friedrich Müller made the first glass sphere for his friend who had lost an eyelid. This glass completely covered the eye, protecting it from harmful environmental influences, and improved visual acuity. After his first successful experience, the glassblower began producing lenses for other clients. The lenses he blew completely followed the shape of the eye and were made in a two-color version. The white glass was adjacent to the white of the eye, and the transparent glass was adjacent to the iris and pupil.
At the beginning of the twentieth century, mass production of glass contact lenses by the German company Carl Zeiss began. At that time, glass lenses were the crown of ophthalmology. However, they had significant ones. The size of the glass shell did not allow the natural flow of oxygen to the cornea of the eye and over time caused serious problems for patients due to hypoxia.
Plastic in the eye
In 1939, the Hungarian doctor István Györffy proposed making lenses from plastic, and a little later his colleague Kevin Tauki reduced their size for greater convenience and comfort for users. But the new model also had its drawbacks. Hard plastic was inconvenient to use, so the appearance of the first soft contact lens was perceived as a breakthrough of sorts.
Czech polymer
The material from which modernized lenses began to be made in the fifties of the twentieth century was invented by the Czech scientist Otto Wichterle. He created a polymer capable of transmitting oxygen and absorbing liquid. In 1988, the famous company Johnson & Johnson released the first batch of daily lenses, which received great recognition from customers.
Today, lenses are made from silicone hydrogel. You can even buy them in vending machines, and most importantly, with their help you can not only improve your vision, but change your eye color to suit your mood. However, the invention of hydrophobic lenses did not put an end to vision correction; specialists are working on a material that would not be rejected by the mucous membrane and would be completely devoid of the disadvantages of modern silicones.
(that is, to increase visual acuity), with the exception of decorative and cosmetic contact lenses - they can not only correct vision, but also decorate the eyes.
Contact lenses, according to experts, are worn by about 125 million people in the world. The method of vision correction using contact lenses is called contact vision correction.
More than 40% of contact lens wearers are young people aged 12 to 25 years. And among those who put on contact lenses for the first time, the proportion of young people under the age of 35 is almost 90%, while 70% of them are women.
Story
The idea of using contact correction was first expressed by Leonardo da Vinci in 1508. The archive of his works contains a drawing of an eye with a bath filled with water - a prototype of modern contact lenses. In 1888, Adolf Fick described the first glass lens with optical power. The first lens was made and introduced into medical practice by the German inventor August Muller.
Until the 1960s, contact lenses were made only from plexiglass (PMMA). Rigid PMMA lenses were uncomfortable to wear, caused a feeling of a foreign body in the eye and did not allow oxygen to reach the cornea, which is necessary for its normal functioning.
- Material
- Radius of Curvature (BC, BCR)
- Lens Diameter (D, OAD)
- Optical power
- Cylinder axes
- Lens Center Thickness
- Wearing mode
- Replacement frequency
- Design
- 1 day (one-day contact lenses),
- 1-2 weeks,
- 1 month (monthly replacement lenses),
- 3 or 6 months,
- 1 year (traditional lenses).
Long-term wear lenses without replacement (6-12 months) are packaged in bottles. Lenses that need to be replaced more frequently are packaged in blisters.
- daytime (lenses are put on in the morning and removed before bedtime),
- prolonged (lenses are worn for 7 days and not removed at night),
- flexible (lenses are worn for 1-2 days without removing),
- continuous (it is possible to wear lenses continuously for up to 30 days without removing them at night; the mode is allowed only for some silicone hydrogel lenses; its use requires consultation with an ophthalmologist).
Contact lens design:
- Spherical myopia and hypermetropia.
- Toric contact lenses are used to correct myopia and hypermetropia in the presence of astigmatism.
- Multifocal contact lenses are used to correct presbyopia.
Aspherical design can be used in all types of lenses to improve vision quality.
Various materials are used to make contact lenses. Most of them are hydrogel polymers. Silicone hydrogel There are only about 10 materials.
Contact lens material largely determines its properties. The main characteristics of the material include water content And oxygen permeability.
Depending on the water content in lens material they are divided into:
- low water content lenses (<50 %),
- lenses with average water content (about 50%),
- lenses with high water content (>50%).
For hydrogel contact lenses, the higher the water content, the more oxygen they allow to reach the cornea of the eye, which has a positive effect on eye health. However, as the water content increases, hydrogel lenses become too soft and difficult to handle. Therefore, the maximum water content in hydrogel lenses does not exceed 70%. For silicone hydrogel lenses, oxygen transmission is not related to water content.
Contact lens ability let oxygen through characterized by a special coefficient Dk/t (Dk is the oxygen permeability of the lens material, and t is the thickness of the lens in the center). For hydrogel lenses, Dk/t is usually in the range of 20-30 units. This is enough for daytime wear. In order for lenses to be left on the eyes overnight, much higher values are required. Silicone hydrogel contact lenses have a Dk/t of the order of 70-170 units.
Radius of curvature paired with Diameter contact lens affects how the lens “fits” in the eye. Typically lenses are available in one or two radii of curvature. Poor fit of a contact lens due to a discrepancy between the radius of curvature of the lens and the shape of the cornea can lead to refusal to wear contact lenses.
Basic optical parameters contact lens: sphere power (in diopters, with a "+" or "-" sign), cylinder power (in diopters) and cylinder axis position (in degrees). The last two parameters are indicated for toric contact lenses used to correct astigmatism.
Designations for eyes in the recipe: O.D.- right eye, OS- left eye.
The parameters of contact lenses for the left and right eyes of one patient, generally speaking, may not be the same.
Hygiene and contraindications
With the correct medical selection, compliance with all recommendations for wearing time, handling and processing, contact lenses cannot harm vision.
If hygiene rules are not followed or lenses are processed incorrectly, the mucous membrane of the eye may become infected. If the terms of wearing are not observed, regular replacement lenses are worn out regularly, or lenses with low oxygen permeability are used, gradual growth of blood vessels into the cornea of the eye (corneal neovascularization) and other complications are possible, which are often irreversible and are a contraindication to further wearing contact lenses.
Anyone who wears contact lenses should undergo preventive examinations by an ophthalmologist at least once a year.
Wearing contact lenses in frosty weather is not contraindicated.
Colored contact lenses
Manufacturers of contact lenses sometimes emphasize their cosmetic role in advertising.
Colored contact lenses are used to radically change the color of the iris, tint- respectively, to enhance or change the shade. Colored and tinted contact lenses come with both diopters, for correcting vision and changing the shade of the eyes at the same time, and “zero”, for those who want to achieve only a cosmetic effect.
Colored lenses do not affect the color of the perception of surrounding objects, since they are transparent in the center.
Precautionary measures
If the lenses are chosen incorrectly and “float” in the eye, interference and discomfort are inevitable, you should consult a doctor. It is not recommended to wear colored and tinted lenses in the twilight and dark, since the human pupil dilates in insufficient lighting, and the colored part of the lens comes into view, which is perceived as interference, a veil before the eyes.
It is prohibited to drive a car wearing colored or tinted contact lenses. and also perform other work that requires increased visual attention and speed of motor reactions.
Swimming and bathing in lenses is only possible if you use sealed swimming goggles or a mask. You cannot go to the sauna or bathhouse while wearing lenses. If you took a shower or swam wearing lenses (without glasses or a mask), you must immediately change them for a fresh pair.
Largest contact lens manufacturers
- Cooper Vision
- Maxima Optics
- Interojo
Production of contact lenses
There are several methods for making lenses: centrifugal molding, turning, casting, as well as methods combining these techniques.
- Turning- “dry” polymerized workpieces are processed on a lathe. Using computer control programs, lenses of complex geometry with two or more radii of curvature are produced. After turning, the lenses are polished, hydrated (saturated with water) to the required parameters and undergo chemical cleaning. At the end of the cycle, the lens is tinted, checked, sterilized, packaged and labeled.
- Casting- a less labor-intensive method than turning. First, a metal matrix mold is made, each set of lens parameters has its own. Plastic copy molds are cast using the matrix, into which a liquid polymer is poured, which hardens under the influence of ultraviolet radiation. The finished lens is polished, hydrated, tinted, sterilized and packaged.
- Centrifugal molding- the oldest method of producing soft contact lenses, but is still used today. The liquid polymer is injected into a mold rotating at a certain speed, where it is immediately exposed to temperature and/or ultraviolet radiation, causing it to harden. The workpiece is removed from the mold, hydrated and subjected to the same processing as during turning.
One example combined method contact lens production - Reversible process III. With this method, the front surface of the lens is obtained by centrifugal molding, and the rear surface is obtained by turning.
Notes
Links
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Lenses made of glass or plastic; are applied to the eyeball to correct various visual impairments, e.g. astigmatism... Big Encyclopedic Dictionary
Helps you see all the colors of the world, while they themselves remain invisible. Gives comfort and self-confidence. They can even radically change their appearance in a matter of seconds.
These are contact lenses. More several centuries ago Great minds around the world began to dream of a magical device that could instantly correct a person's vision.
Leonardo da Vinci, Rene Descartes, Thomas Jung and many other scientists worked for many years to make this dream come true.
The history of creating prototypes of contact lenses for the eyes
The appearance of contact lenses for the eyes was preceded by several large-scale discoveries.
Rene Descartes
In 1637 French physicist, mathematician, physiologist Rene Descartes invented an optical instrument like a telescope.
It was a tube filled with water into which a magnifying glass was inserted. Opposite side the device was applied to the visual organ. Direct contact with the cornea of the eye is the only similarity between Descartes' invention and a contact lens. This tube was quite traumatic and extremely inconvenient in use (the person who used it could not even blink).
Thomas Young
In 1801 English physicist Thomas Young perfected Descartes' invention. The tube invented by Jung was shorter, allowing light rays to be focused on the retina. To mount the device, Jung used wax.
John Herschel
Jung, in turn, inspired the English scientist John Herschel to systematize all the inventions of that time in the field of vision correction.
In 1823 Herschel described the design of the corneal lens in detail. A in 1845— proved the possibility of treating astigmatism using a device in contact with the cornea of the eye.
The scientist called this device "optical capsule" and argued that it should be transparent, made of glass or some jelly-like material and follow the shape of the cornea.
Herschel limited himself to theoretical research, but many of the principles he described formed the basis for the manufacture of modern contact products.
Siegrist and Lonstein
At the end of the 19th century English Lonstein and Siegrist created a device for treating deformed corneas - hydroscope. These were large glasses, similar to a scuba diver's mask. The hydroscope fit hermetically to the face and was in contact with the eyes through the liquid with which it was filled. The glasses were bulky and uncomfortable; wearing them for a long time damaged the skin around the eyes: it softened due to constant contact with water.
When were the first models that rest on the eye invented?
The invention of lenses that stay on the eyes is thanks to several outstanding individuals.
Adolf Fick
1888 is the date of invention of the first products that can truly be called contact lenses. Such a product was described by a famous Swiss doctor Adolphe Gaston Evgeny Fick. It was made of glass and weighed about 0.5 grams. The scientist did a lot of work to bring his idea to life.
He started from the manufacture of corneal optical products(which cover only the cornea of the eye), and a little later he created scleral(which are partially adjacent to the sclera).
The scientist preferred the latter, since they were more securely attached to the eye. Manufacturing was a very painstaking process, they cast on the basis of plaster casts of cadaveric eyes.
First, Fick tested them on animals, and then decided to “try them on” on people, and tested them on himself. He studied in detail the effect of his invention on the eye, described in detail the adaptation period and compiled a very detailed manual for the use of his lenses.
In 1896 Adolf Fick's textbook was published, where it was described eight directions development of the science of vision correction. Fick lenses used to treat astigmatism and keratoconus.
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Eugene Calt
March 20, 1888 Frenchman Eugene Calt announced the invention of special corneal lens products for the treatment of keratoconus. In fact, Kalt lenses could not be called corneal, because they also had an opaque part that rested on the sclera. Kalt's invention It stayed firmly on the eye, but caused irritation to the eyelids.
August Müller
German inventor August Müller did not know about the discoveries of Adolf Fick, so he began work on creating contact lenses literally from scratch. And he tested his inventions before his own eyes. In 1889 Müller was the first to manufacture products using the method of casts from the visual organs.
Photo 1. One of the first prototypes of scleral contact lenses. The products were made of glass.
This technology was adopted by many of his followers. And he was also the first to think over the problem of lack of oxygen under the lens eyepiece. Müller tried to solve this issue by filling the space between the lens and the cornea with water, but the water caused swelling of the cornea.
Carl Zeiss
In 1913 The factory of the German inventor began mass production of contact products Carl Zeiss. Zeiss produced polished products, which were better tolerated by the eye than Müller lenses. Corneal lenses were not very successful because they did not fit well on the eye. There were no such problems with scleral ones.
In the 20s of the twentieth century The factory began producing different sets from which doctors could choose lenses individually for each patient. Of course, this selection was quite approximate.
In what year did the method of vision correction with lenses appear?
In 1938 Americans D. Mahler and T. Obrig began a new chapter in the history of vision correction.
They decided to use it to make scleral lenses synthetic plastic polymethyl methacrylate, or for short PMMA.
This made it possible to make lenses almost weightless. Now they fit perfectly on the eye and did not slip, unlike glass ones.
This advantage of PMMA allowed the transition to the production of corneal types. AND in 1947 plastic corneal lenses appeared with a diameter of 1.2 centimeters. They were much lighter and more comfortable than scleral ones. With its obvious advantages plastic also had disadvantages: it caused severe discomfort and irritated the cornea of the eye.
In the sixties of the twentieth century German ophthalmologist Otto Wichterle patented a new material for making lenses - synthetic polymers. Thanks to him, the lenses became not only very light, but also soft. Now they were practically not felt on the eye. Patient confidence in this type of vision correction has increased significantly.
The state of lens products in the modern world
Nowadays, ophthalmology has reached the highest level, and the choice of contact lenses is huge. You can choose rigid types: they are either gas-permeable or gas-tight. Or stick to more popular soft lenses. There are two varieties soft types: hydrogel- very elastic, elastic and smooth, and silicone hydrogel- allow air to pass through well and keep their shape.
Photo 2. Modern soft contact lenses. The products are very light, almost not felt on the eyes.
There are several types of products that differ in the mode of wearing and replacement period. Modern types of lens eyepieces are distinguished even by purpose. In addition to optical ones, designed to correct vision, there are also cosmetic ones, designed to change eye color.
Attention! The main advantage of a contact lens over glasses is no distortion of objects.
When were colored eye lenses invented?
For the first time such decorative lenses appeared in 1981. The corporation began producing them CIBI Vision. It is interesting that initially colored products were produced not to change the appearance, but for more convenient handling, because such a product is more difficult to lose than a transparent one.
In 1984 CIBI Vision began producing lenses to change the color of light eyes. People with dark eyes were given the opportunity to try on a different shade only in 1991.
Contact lenses- small lenses made from transparent materials, worn directly on the eyes to correct vision (that is, to increase visual acuity), with the exception of decorative and cosmetic contact lenses - they can not only correct vision, but also decorate the eyes.
Contact lenses, according to experts, are worn by about 125 million people (2%) in the world.
People wear contact lenses for functional or optical reasons. Compared to glasses, contact lenses generally provide better peripheral vision and do not collect moisture such as rain, snow, condensation or sweat (extreme weather). This makes them ideal for sports and outdoor activities. In addition, there are conditions such as keratoconus and aniseikonia that are generally corrected better with contact lenses than with glasses.
More than 40% of contact lens wearers are young people aged 12 to 25 years. And among those who put on contact lenses for the first time, the proportion of young people under the age of 35 is almost 90%, with 70% of them being women.
Difference from glasses
The main optical difference: the lenses leave visible objects without distortion (distortion) due to their close location to the eye. Glasses change the shape and size of objects.
Story
The idea of using contact correction was first expressed by Leonardo da Vinci in 1508. In the archive of his works, they found drawings of a ball filled with water, through which a person with poor eyesight could see better. In his notes there are also diagrams of lenses - a prototype of modern contact lenses. In 1637, Rene Descartes published his work, in which he presented drawings of an optical device. This device consisted of a glass tube filled with water, a magnifying glass was attached to one end, and the other end was placed against the eye. Subsequently, the English physicist Thomas Young improved Rene Descartes' device by using a shorter tube, thereby compensating for the deficiencies of refraction. In 1888, the German physiologist Adolf Gaston Eugen Fick described the first glass lens with optical power. The first lens was made and introduced into medical practice in 1889 by the German ophthalmologist and inventor August Müller. He defended his doctoral dissertation on the topic “Glasses and corneal lenses.” August Müller used the first lenses to correct vision for myopia.
Until the 1960s, contact lenses were made only from organic glass (PMMA). Rigid PMMA lenses were uncomfortable to wear, caused a sensation of a foreign body in the eye and did not allow oxygen to reach the cornea, which is necessary for its normal functioning.
At the beginning of 2016, Alcon released the world's first fourth generation contact lenses - water-gradient contact lenses, with moisture content up to 100% and oxygen permeability 156 Dk/t
Types of contact lenses
There are various classifications of contact lenses: according to the material from which they are made, according to the frequency of replacement (the period after which the lenses are replaced with new ones), wearing mode (daytime, flexible, extended, continuous), design (spherical, toric, multifocal), degree transparency (transparent, colored, decorative).
In general, contact lenses are divided into two large groups:
- Soft contact lenses
- Hard contact lenses.
Soft contact lenses are worn by approximately 90% of the world's contact lens wearers. Soft contact lenses, in turn, are divided into 2 classes: hydrogel lenses and silicone hydrogel lenses.
Rigid contact lenses are used mainly for vision correction in difficult cases (for example, with high degrees of astigmatism, keratoconus) and in orthokeratology. Rigid lenses allow you to achieve increased visual acuity due to the fact that they retain their shape. Such lenses are made from polymers that provide a high degree of oxygen transmission to the cornea of the eye, which is why they are called rigid gas permeable contact lenses. [ ]
Colored and tinted contact lenses
Colored contact lenses are used to radically change the color of the iris, tint- respectively, to enhance or change the shade. Colored and tinted contact lenses come with both diopters, for correcting vision and changing the shade of the eyes at the same time, and “zero”, for those who want to achieve only a cosmetic effect.
Colored lenses do not affect the color of the perception of surrounding objects, since they are transparent in the center.
It is not recommended to wear colored contact lenses in the twilight and dark, since the human pupil dilates in insufficient light, and the colored part of the lens comes into view, which is perceived as interference, a veil before the eyes.
Basic parameters of soft contact lenses
Contact lenses are characterized by the following main parameters:
- Material
- Radius of Curvature (BC, BCR)
- Lens Diameter (D, OAD)
- Optical power
- Cylinder axes
- Lens Center Thickness
- Wearing mode
- Replacement frequency
- Design
- 1 day (one-day contact lenses),
- 1-2 weeks,
- 1 month (monthly replacement lenses),
- 3 or 6 months,
- 1 year (traditional lenses).
Long-term wear lenses without replacement (6-12 months) are packaged in bottles. Lenses that need to be replaced more frequently are packaged in blisters.
- daytime (lenses are put on in the morning and removed before bedtime),
- prolonged (lenses are worn for 7 days and not removed at night),
- flexible (lenses are worn for 1-2 days without removing),
- continuous (it is possible to wear lenses continuously for up to 30 days without removing them at night; the mode is allowed only for some silicone hydrogel lenses; its use requires consultation with an ophthalmologist).
- night (put on 15 minutes before bedtime and take off in the morning. During the day, the patient sees perfectly without lenses, subject to an 8-hour sleep regimen and wearing it every day.)
- Spherical myopia and hypermetropia.
- Toric contact lenses are used to correct myopia and hypermetropia in the presence of astigmatism.
- Multifocal contact lenses are used to correct presbyopia.
To improve the quality of vision, aspherical design can be used in all types of lenses.
Various materials are used to make contact lenses. Most of them are hydrogel polymers. Silicone hydrogel There are only about 10 materials.
Contact lens material largely determines its properties. The main characteristics of the material include water content And oxygen permeability.
Depending on the water content in lens material they are divided into:
- low water content lenses (<50 %),
- lenses with average water content (about 50%),
- lenses with high water content (>50%).
For hydrogel contact lenses, the higher the water content, the more oxygen they allow to reach the cornea of the eye, which has a positive effect on eye health. However, as the water content increases, hydrogel lenses become too soft and difficult to handle. Therefore, the maximum water content in hydrogel lenses does not exceed 70%.
For silicone hydrogel lenses, oxygen transmission is not related to water content.
Contact lens ability let oxygen through characterized by a special coefficient Dk/t (Dk is the oxygen permeability of the lens material, and t is the thickness of the lens in the center). For hydrogel lenses, Dk/t is usually in the range of 20-30 units. This is enough for daytime wear. In order for lenses to be left on the eyes overnight, much higher values are required. Silicone hydrogel contact lenses have a Dk/t of the order of 70-170 units.
Radius of curvature paired with Diameter contact lens affects how the lens “fits” in the eye. Typically lenses are available in one or two radii of curvature. Poor fit of a contact lens due to a discrepancy between the radius of curvature of the lens and the shape of the cornea can lead to refusal to wear contact lenses.
Basic optical parameters contact lens: sphere power (in diopters, with a "+" or "-" sign), cylinder power (in diopters) and cylinder axis position (in degrees). The last two parameters are indicated for toric contact lenses used to correct astigmatism.
Designations for eyes in the recipe: O.D.- right eye, OS- left eye.
The parameters of contact lenses for the left and right eyes of one patient may not be the same.
Terms of use
If the lenses are chosen incorrectly and “float” in the eye, interference and discomfort are inevitable, you should consult a doctor. If the radius of curvature is too large, the lenses seem to “float” slightly in the eye, and if they are too small, they “get stuck” in one position, become fixed and do not provide this part of the cornea with the necessary oxygen supply. In both cases, the lenses should be changed: correctly fitted lenses may move slightly with some blinking (that is, they are not rigidly fixed), but most of the time they will remain in place in the center of the cornea. Long-term wearing of lenses with a small radius of curvature leads to oxygen starvation of the cornea and increases the risk of keratitis, since pathogens do not survive with sufficient oxygen.
It is believed that everyone who wears contact lenses needs to undergo preventive examinations by an ophthalmologist at least once a year.
Possible complications
The use of contact lenses can lead to the following types of complications:
- infectious diseases (