Excimer lasers: device, application in medicine
In this article we consider the advantages of excimer lasers. To date, medicine has a wide range of all kinds of laser equipment for treating complex diseases in hard-to-reach areas of the human body. Laser operations help to achieve the effect of minimally invasive and painless, which has a huge advantage over those surgical interventions that are performed manually during cavitary operations, which are very traumatic, fraught with high blood loss, and long-term rehabilitation after them.
What is a laser?
A laser is a special quantum generator that emits a narrow light beam. Laser devices open incredible possibilities for transmitting energies to different distances at high speed. The ordinary light, which can be perceived by human vision, is a small bundle of light that spreads in different directions. If these beams are concentrated by means of a lens or a mirror, a large beam of light particles is obtained, but even it can not be compared with a laser beam, which consists of quantum particles,
Excimer lasers are widely used in many areas of human activity with the help of colossal developments of scientists all over the world and have the following varieties:
- dye lasers;
- metal vapor lasers;
- free-electron lasers.
This variety is an ultraviolet gas laser, which is widely used in the field of eye surgery. With this device, doctors perform laser vision correction.
The term excimer means an "excited dimer" and characterizes the type of material that is used as its working fluid. For the first time in the USSR, a similar device was presented in 1971 by scientists VA Danilichev, N. Basov and Yu. M. Popov in Moscow. As a working medium of such a laser, a xenon dimer was used, which was excited by an electron beam in order to obtain radiation with a specific wavelength. After a while, noble gases with halogens were used for this purpose, and this was done in 1975 in one of the US research laboratories by the scientists J. Hart and S. Searles.
People often ask why an excimer laser is used to correct vision.
It was found that the excimer molecule produces laser radiation due to the fact that it is in an excited "attractive" state, as well as in a "repulsive" state. This action can be explained by the fact that xenon or krypton( noble gases) have a high inertia and, as a rule, never form chemical compounds. Electric discharge leads them into an excited state, so that they can form molecules either between themselves, or with halogens, for example, chlorine or fluorine. The appearance of molecules in an excited state creates, as a rule, the so-called population inversion, and such a molecule gives up its energy, which is forced or spontaneous emission. After this, the given molecule returns to the ground state and breaks up into atoms. The excimer laser device is unique.
The term "dimer" is usually used when identical atoms join together, but in most excimer lasers of the present, noble gas and halogen compounds are used. Nevertheless, these compounds are also called dimers for all lasers of similar design. How does an excimer laser work? We will now consider this.
Principle of operation of excimer laser
This laser is the main protagonist of PRK and LASIK.Its working body is an inert and halogen gas. When a high voltage penetrates into the mixture of these gases, one halogen atom and one atom of an inert gas combine to form a diatomic molecule. It is in an extremely excited state and after a thousandth of a second breaks up into atoms, which leads to the appearance of a light wave in the UV range.
This principle of excimer laser action has found wide application in medicine, since ultraviolet radiation affects organic tissues, for example, on the cornea, in such a way that the bonds between molecules that lead to the transfer of tissues from solid to gaseous state are disconnected. This process is called "photoablation".
wave range All existing models of this type operate in the same wavelength range and differ only in the width of the light beam and in the composition of the working fluid. Excimer laser for correction of vision is used most often. But there are other areas of its use.
The first had a diameter of the light beam, which was equal to the diameter of the surface on which evaporation was carried out. A wide range of the beam and its heterogeneity caused the same heterogeneity of the upper layers of the cornea, as well as an increase in temperature on its surface. This process was accompanied by injuries and burns. This situation was corrected by the creation of an excimer laser. In MNTK "Microsurgery of the eye" use it a very long time.
New generation lasers underwent a long process of modernization, during which the diameter of the light beam was reduced, and a special rotational-scanning delivery system was created to the eye of laser radiation. Consider how excimer lasers are used by doctors.
Application in medicine
In a cross-section such a laser beam looks like a spot moving around in a circle, removing the upper layers of the cornea, and also giving it another radius of curvature. In the ablation zone, the temperature does not rise, because the effect is short-lived. As a result of the operation, an even and clear surface of the cornea is observed. Excimer laser in ophthalmology is irreplaceable.
The surgical surgeon determines in advance the amount of energy that will be delivered to the cornea and the depth to which the excimer laser will be exposed. From here, a specialist can plan the progress of the process in advance and assume what result will be obtained after the operation.
Laser vision correction
How does the excimer laser work in ophthalmology? At the heart of the popular technique today is the so-called computer re-profiling of the cornea, which is the main optical lens of the human eye. The excimer laser, which is acted on by it, smooths the surface of the cornea, removing the upper layers and, thus, eliminating all defects present on it. In this case, normal conditions arise for the eye to get the right images, creating the correctness of the refraction of light. People who have undergone such a procedure, see as anyone who has an initially good vision.
The procedure for re-profiling the cornea does not cause high temperatures on its surface, which can be detrimental to living tissues. And, as most people believe, there is no so-called burning out of the upper layers of the cornea.
The most important advantage of excimer lasers is that their use for vision correction allows to obtain an ideal result and to correct practical all existing corneal anomalies. These devices are so highly accurate that they allow "photochemical ablation" of the upper layers.
For example, if this process is performed on the central area of the cornea, then its shape becomes almost flat, and this helps correct myopia. If in the process of vision correction corneal layers in the periphery zone evaporate, then its shape becomes more rounded, and this, in turn, corrects hyperopia. Astigmatism is corrected by dosing the upper layers of the cornea in various parts of the cornea. Modern excimer lasers, which are widely used in refractive eye microsurgery, guarantee a high quality surface that undergoes photoblation.
Uses in medicine
Excimer lasers, as they are today, appeared quite recently, but already now they help people around the world get rid of vision problems such as myopia, hyperopia, astigmatism. This solution, for the first time in many years of creating such equipment, meets all the requirements of painlessness, maximum safety and efficiency.
Eye diseases that are treated by applying
The field of ophthalmic surgery, which deals with the elimination of anomalies of the human eye, is called refractive surgery, and similar disorders are caused by anomalies of ametropia and refraction.
According to specialists, two types of refraction are distinguished:
- emmetropia, which characterizes normal vision;
- ametropia, consisting in abnormal vision.
Ametropia, in turn, includes several subspecies:
- myopia( nearsightedness);
- astigmatism - getting the eye of a distorted image when the cornea has an irregular curvature, and the light ray flux becomes uneven in different areas of its surface;
- hypermetropia( hyperopia).
Astigmatism is of two kinds - hypermetropic, which is close to farsightedness, myopic, similar to myopia and mixed.
In order to correctly represent the essence of refractive manipulation, it is necessary to know the anatomy of the human eye minimally. The optics system of the eye consists of three main elements - the cornea, the lens, which are the light-refractory parts, and also the retina, which is the light-sensing part. In order for the resulting image to become clear and sharp, the retina is in the focus of the ball. However, if it is in front of the focus, and this happens with farsightedness, or behind it, what happens with myopia, the resulting image becomes fuzzy and significantly blurred.
In humans, the optics of the eye can change during life, in particular from the moment of birth and up to 16-20 years it changes due to the growth and increase in the size of the eyeball, as well as under the influence of some factors that may lead to the formation of certainanomalies. Thus, the patients of the surgeon, engaged in refraction of the eye, most often become adults.
Contraindications to the procedure of vision correction with excimer beam
Eye correction with excimer laser is not shown to all people with visual impairment. Prohibition of the application of this procedure are:
- ophthalmic diseases( glaucoma, cataract, retinal deformation);
- diseases that prevent normal healing of wounds( arthritis, diabetes, autoimmune diseases, etc.);
- heart disease and vascular system;
- retinal detachment;
- age presbyopia;
- pregnancy and breastfeeding;
- children under 18 years;
- spasm of accommodation;
- progressive changes in eye refraction;
- inflammatory processes in the body, including those relating directly to the eye.
Possible complications after application of
All existing techniques for excimer laser treatment today are characterized by high safety and special efficiency. Nevertheless, there are a number of complications that can occur after surgery with the use of similar techniques. These include:
- Partial or abnormal growth of a part of the cornea, after which it is not possible to increase this part again.
- The so-called dry eye syndrome, when the patient has redness and pain in the eye. This complication can occur if the nerve endings that are responsible for the development of tears are damaged in the course of vision correction.
- A variety of vision disorders, for example, double vision or decreased vision in the dark, a violation of the perception of colors or the appearance of a light halo.
- Weakened or softened cornea, which can occur as a few months after surgery, and after a few years.
Excimer laser in dermatology
The effect of a low-frequency laser on the skin is extremely positive. This is due to the following effects:
That is, there is a certain biostimulating mechanism of action of laser radiation with low power.
Successfully treated with excimer laser vitiligo. Pigmented spots on the skin very quickly smooth out.