From Big Medical Encyclopedia

LASER (an abbreviation from initial letters English. Light Amplification by Stimulated Emission of Radiation - strengthening of light stimulated radiation; synonym optical quantum generator) — the technical device emitting the electromagnetic radiation focused in the form of a bunch in the range from infrared to ultra-violet, having big energy and biological effect. L. were created in 1955 by N. G. Basov, A. M. Prokhorov (USSR) and Ch. Townes (Ch. Townes, the USA) conferred the Nobel Prize of 1964 for this invention.

Fig. 1. Schematic diagram of the solid-state laser: 1 and 4 — the reflecting mirrors of the resonator (the mirror 4 — is translucent); 2 — a flashlight valve of a rating; 3 — a working body (a ruby core); 5 — the condenser; 6 — the power supply.

Bodies of L. the working body, or the active environment, a lamp of a rating, the mirror resonator (fig. 1) are. Laser radiation can be continuous and pulse. Semiconductor L. can work in those and other modes. As a result of strong light flash of a lamp of a rating electrons of active agent pass from a quiet state into excited. Working at each other, they create an avalanche of light photons. Being reflected from resonant screens, these photons, punching the translucent mirror screen, leave a narrow monochromatic light bunch of high energy.

Working body of L. can be firm (crystals of an artificial ruby with additive of chrome, some salts tungsten and molybdenic to - t, different types of glasses with impurity of neodymium and some other elements, etc.), liquid (pyridine, benzene, toluene, naphthalene bromide, nitrobenzene, etc.), gas (mix of helium and neon, helium and vapors of cadmium, argon, krypton, carbon dioxide gas, etc.).

In excited state it is possible to apply the light radiation, a cathode rays, a flow of radioactive particles, chemical reaction to transfer of atoms of a working body.

If to present the active environment as a crystal of an artificial ruby with impurity of chrome, parallel end faces to-rogo are issued in the form of a mirror with internal reflection and one of them translucent, and to light this crystal with powerful flash of a lamp of a rating, then as a result of such powerful zasvet or as it is accepted to call, an optical rating, the bigger number of atoms of chrome will turn into excited state.

Being returned to a ground state, atom of chrome spontaneously radiates a photon which faces the excited atom of chrome, beating out from it other photon. These photons, meeting in turn other excited atoms of chrome, again beat out photons, and this process lavinno accrues. Flow of photons, repeatedly being reflected from mirror end faces, everything increases until the energy density of radiation does not reach the limiting value sufficient for overcoming a translucent mirror, and wavelength to-rogo 694,3 nanometers and duration of an impulse of 0,5 — 1,0 ms with energy from shares to hundreds of joules will escape outside in the form of an impulse of the monochromatic coherent (strictly directed) radiation.

To estimate energy of flash of L. it is possible on the following example: the energy density, total on a range, on the surface of the Sun makes 10 4 W/cm 2 , and the focused beam from L. 1 MW creates a radiation intensity in focus to 10 13 W/cm 2 .

Monochromaticity, coherence, the small angle of discrepancy of a beam, a possibility of optical focusing allow to receive high concentration of energy.

The focused beam of L. it can be directed to the area of several micron. It reaches enormous concentration of energy and extremely high temperature in object of radiation is created. Laser radiation melts steel and diamond, destroys any material.

Laser devices and areas of their use

Special characteristics of laser radiation — the high orientation, coherence and monochromaticity — open almost great opportunities for its use in various areas spiders, technicians and medicine.

Various L are applied to the medical purposes., which power of radiation is defined by problems of operational or therapeutic treatment. Depending on radiation intensity and features of interaction it with different fabrics effects of coagulation, an extirpation, stimulation and regeneration are reached. In surgery, oncology and Ophthalmolum, practice L are applied. tens watts, and for obtaining the stimulating and antiinflammatory effects — L. tens milliwatts.

By means of L. it is possible to transfer at the same time a huge number of telephone negotiations, to carry out communication both in terrestrial conditions, and in space, to make a location of celestial bodies.

Small discrepancy of a beam of L. allows to apply them in surveying practice, construction of large engineering constructions, to landing of airplanes, in mechanical engineering. Gas L. find application for obtaining volume images (holography). In geodetic practice various types of laser svetodalnomer are widely used. L. initiation of chemical reactions, etc. are applied in meteorology, to control of environmental pollution, in measuring and computer facilities, instrument making, to dimensional processing of microelectronic schemes.

In laser technology both solid-state, and gas L find application. pulse and continuous action. For cutting, drillings and weldings of various high-strength materials — staly, alloys, diamonds, hour stones — are issued laser machines on carbon dioxide gas (LUND-100, TILU-1, the Impulse), on nitrogen (Signal-3), on a ruby (LUCh-1M, K-ZM, LUCh-1 P, SU-1), on neodymium glass (Quantum-9, Corundum-1, SLS-10, the Cornel), etc. In the majority of processes of laser technology the thermal effect of light caused by its absorption by the processed material is used. Optical systems are applied to increase in flux density of radiation and localization of a zone of processing. Features of laser technology following: the high density of a radiation energy in a zone of processing giving for a short time necessary thermal effect; the locality of the influencing radiation caused by a possibility of its focusing and light bunches of extremely small diameter; the small heat-affected zone provided with short-term influence of radiation; a possibility of conducting process in any transparent environment, through windows tekhnol. cameras and so forth.

Power of radiation of L., the systems of targeting and communication applied to instrumentations, it is small, about 1 — 80 MW. For pilot studies (measurement of flow rates of liquids, studying of crystals, etc.) powerful L are used., generating radiation in pulsed operation with a peak power from kilowatts to hectowatts and lasting impulse 10 - 9 — 10 - 4 sec. For processing of materials (cutting, welding, an insertion of openings, etc.) various H.p. by a power output from 1 to 1000 watts and more are applied.

Laser devices considerably increase efficiency of work. So, laser cutting gives considerable economy of raw materials, the instant punched hole of openings in any materials facilitates work of the driller, the laser method of production of chips improves quality of products etc. It is possible to claim that L. became one of the widespread devices used to the scientific, technical and medical purposes.

The mechanism of action of a laser beam on biol, fabrics is based that energy of a light bunch sharply increases temperature on a small body part. Temperature in the irradiated place, according to J. P. Minton, can rise to 394 ° and therefore patholologically the changed site instantly burns down and evaporates. Thermal impact on surrounding fabrics at the same time extends to very small distance since width of the direct monochromatic focused bunch of radiation is equal

to 0,01 mm. Under the influence of laser radiation there is not only a coagulation of proteins of living tissue, but also its explosive destruction from action of a peculiar shockwave. This shockwave is formed as a result at high temperature the intercellular lymph instantly turns into gaseous state. Features biol, actions depend on wavelength, duration of impulses, power, energy of laser radiation, and also on structure and properties of the irradiated fabrics. Coloring (pigmentation), thickness, density, a degree of admission blood of fabrics, them fiziol, a state and existence in them patol, changes matter. The more the power of laser radiation, the more deeply it gets and the stronger works.

In pilot studies influence of light radiation of various range on cells, fabrics and bodies was studied (skin, muscles, bones, internals and dr). results to-rogo differ from thermal and beam influences. After immediate effect of laser radiation on fabrics and bodies in them there are limited centers of defeat of various area and depth depending on character of fabric or body. At gistol, studying of the fabrics and bodies which were affected by L., in them it is possible to define three zones morfol, changes: zone of a superficial coagulative necrosis; zone of hemorrhage and hypostasis; zone of dystrophic and necrobiotic changes of a cell.

Lasers in medicine

Development of pulse L., and also L. continuous action, capable to generate light radiation with a big energy density, created conditions for wide use of L. in medicine. By the end of the 70th of 20 century laser radiation began to be applied to diagnosis and treatment in various fields of medicine — surgery (including traumatology, cardiovascular, abdominal surgery, neurosurgery, etc.)> oncology, ophthalmology, stomatology. It is necessary to emphasize that a founder of modern methods of laser microsurgery of an eye is the Soviet ophthalmologist the academician of the USSR Academy of Medical Sciences M. M. Krasnov. Perspectives of practical use of L were outlined. in therapy, physical therapy, etc. Spectrochemical and molecular researches biol, objects are already closely connected with development of laser issue spectroscopy, an absorbing and fluorescent spektrofotometriya with use of the L reconstructed on frequency., laser spectroscopy of combinational light scattering. These methods along with sensitization and the accuracy of measurements reduce a run time of analyses that provided sharp expansion of volume of researches for diagnosis of occupational diseases, control of use of medicamentous means, in the field of forensic medicine, etc. In combination with a fiber optics laser methods of spectroscopy can be applied to raying of a chest cavity, a research of blood vessels, photography of internals for their studying funkts, departures and detection of tumors.

Studying and identification of big molecules (DNA, RNA, etc.) and viruses, immunol, researches, studying of kinetics and biol, activities of microorganisms, microcirculation in blood vessels, measurement of speeds of flows biol, liquids — the main ranges of application of methods of laser Rayleigh and Doppler spectrometry, highly sensitive the express - the methods allowing to perform measurements at extremely low concentrations of the studied particles. By means of L. make microspectral analysis of fabrics, being guided by character of the substance which evaporated under a radiation effect.

Dosimetry of laser radiations

Due to the fluctuations of power of an active body of L., especially gas (e.g., helium - neon), in the course of their operation, and also according to requirements of the accident prevention carry systematically out radiation control by means of the special dosimeters calibrated on standard reference measuring instruments of power, in particular the IMO-2 type, and certified by the public metrological service. The dosimetry allows to define effective therapeutic doses and density of the power causing biol, efficiency of laser radiation.

Lasers in surgery

the First range of application of L. in medicine there was a surgery.


Ability of a beam of L. to cut fabrics allowed to implement it in surgical practice. The bactericidal effect, coagulating properties of «a laser scalpel» formed a basis for its use at operations on went. - kish. a path, parenchymatous bodies, at neurosurgical operations, at the patients suffering from the raised bleeding (hemophilia, a radial illness, etc.).

With success are applied helium - neon and carbon dioxide L. at some surgical diseases and damages: infected, it is long not healing wounds and ulcers, burns, an obliterating endarteritis, the deforming arthrosis, fractures, autotransplantation of skin on burn surfaces, abscesses and phlegmons of soft tissues, etc. Scalpel and Pulsar laser machines are intended for cutting of bones and soft tissues. It is established that the radiation of L. stimulates processes of regeneration, changing duration of phases of a current of a wound process. E.g., after opening of abscesses and processing of walls of cavities of L. time of healing of wounds in comparison with other methods of treatment due to reduction of contamination of a wound surface is considerably reduced, accelerations of clarification of a wound from it is purulent - a necrotic lot and formation of granulations and epithelization. Gistol, and tsitol, researches showed strengthening of reparative processes owing to increase in synthesis of RNA and DNA in cytoplasm of fibroblasts and the maintenance of a glycogen in cytoplasm of neutrophilic leukocytes and macrophages, reduction of quantity of microorganisms and number of microbic associations in wound separated, decrease biol, to activity of pathogenic staphylococcus.


Center of defeat (wound, ulcer, burn surface, etc.) conditionally divide into fields. Each field daily or in 1 — 2 day is irradiated by L. low power (10 — 20 MW) within 5 — 10 min. Course of treatment of 15 — 25 sessions. If necessary in 25 — 30 days it is possible to conduct a repeated course; usually they are not repeated by more than 3 times.

Lasers in oncology

In 1963 — 1965 in the USSR and the SET were made the animal experiments which showed that the radiation of L. it is possible to destroy the intertwined tumors. In 1969 in Ying-those problems of oncology of AN of USSR (Kiev) the first department of laser therapy onkol was open, a profile, equipped with special installation, with the help a cut treated patients with tumors of skin (fig. 2). Further attempts of distribution of laser therapy of tumors and other localization became.


Fig. 2. The laser machine for treatment of tumors: 1 — the light guide for pulse radiation; 2 — the light guide for continuous radiation; 3 — an exhaust system of products of combustion of fabrics.
Fig. 3. A shin of the patient with a melanoma of skin (1 — before laser therapy, 2 — after treatment).

L. apply at treatment of skin benign and malignant tumors, and also some pretumor conditions of female generative organs. Impact on deeply located tumors demands usually their exposure since during the passing through fabrics laser radiation is considerably weakened. Thanks to more intensive light absorption the pigmented tumors — melanomas, hemangiomas, a pigmental nevus, etc. — give in to laser therapy easier, than not pigmented (fig. 3). Methods of use of L are developed. for treatment of tumors of other bodies (a throat, genitalias, a mammary gland, etc.).

Contraindication to use of L. the tumors located about eyes are (because of danger of damage of an organ of sight).


Fig. 4. The patient with pigmental papillomatous a nevus: 1 — before laser therapy; 2 — in 5 weeks after radiation; 3 — in three months.

There are two methods of use of L.: radiation of a tumor for the purpose of a nekrotization and its excision. During the performing treatment with the purpose to cause a necrosis of a tumor make: 1) processing of an object small doses of radiations, iod action of which the site of a tumor collapses, and its other part nekrotizirutsya gradually; 2) radiation by high doses (from 300 to 800 J/cm 2 ); 3) multiple radiation, to-rogo results total death of a tumor. At treatment by method of a nekrotization radiation of skin tumors is begun with the periphery, gradually progressing to the center, usually taking a borderland of normal fabrics 1,0 — 1,5 cm wide. Radiation of all mass of a tumor since unirradiated sites are a source of a regrowth is necessary. The size of a radiation energy is defined by type L. (pulse or continuous action), spectral region and other parameters of radiation, and also features of a tumor (pigmentation, sizes, density, etc.). At treatment of not pigmented tumors it is possible to enter into them the colored compounds strengthening absorption of radiation and destruction of a tumor. Owing to a nekrotization of fabric on site of a skin tumor the black or dark gray crust is formed, edges disappears in 2 — 6 weeks (fig. 4).

At excision of a tumor by means of the laser the good haemo static and aseptic effect is reached. The method is in a stage of development.


Fig. 5. A face of the patient with a carcinoma cutaneum of a forehead (1 — before laser therapy, 2 — after treatment).

L. any tumor available to radiation can be destroyed. At the same time there are no side effects, in particular in the hemopoietic system that gives the chance to treat the patients of advanced age weakened patients and children of early age. At the pigmented tumors only tumor cells selectively collapse, than the sparing influence and favorable results in the cosmetic relation is provided. Radiation can be focused precisely and, therefore, strictly to localize intervention. Haemo static action of laser radiation gives the chance to limit blood losses). The successful result at cancer therapy of skin, on 5 years' observations, is noted in 97% of cases (fig. 5).

Complications: a carbonization

of fabrics at their section.

Lasers in ophthalmology

Traditional pulse unmodulated L. (usually on a ruby) were used till 70th for cauterizations on an eyeground, napr, for the purpose of formation of chorioretinal commissure at treatment and prevention of amotio of a retina, at small tumors etc. At this stage the area of their use was approximately the same that at the photocoagulators using usual (polychromatic, incoherent) a ray of light.

Fig. 1. Argon laser photocoagulator of Model-800 («Coherent Radiation», USA).
Fig. 2. The domestic laser Yataghan-2 ophthalmologic machine (a ruby lazer with passive modulation of good quality).

In the 70th in ophthalmology with success new types L were applied. (tsvetn. fig. 1 and 2): gas L. constant action, the modulated H.p. «huge» impulses («cold» L.), L. on dyes and some other. It considerably broadened area a wedge, uses of L. on an eye — active intervention on internal covers of an eye without opening of his cavity became possible.

The big practical importance the following areas present a wedge, to laser ophthalmology.

1. It is known that vascular diseases of an eyeground leave (and in a number of the countries already came out) on top among the reasons of an incurable blindness. Among them the diabetic retinopathy has a wide spread occurance, edges develops almost at all patients with diabetes lasting disease of 17 — 20 years.

Patients usually lose sight as a result of repeated intraocular hemorrhages from the changed vessels neogenic patholologically. By means of a laser bunch (the best results are yielded gas, napr, argon, by L. constant action) coagulations are exposed as the changed vessels with sites of transudation, and zone of the neogenic vessels especially subject to a gap. The successful result remaining for a number of years is noted approximately at 50% of patients. Usually coagulate also not affected areas of a retina which have no paramount funkts, values (pan-retinal coagulation).

Fig. 7 and 8. Laser therapy of the central dystrophy of a retina at occlusion of a nizhnevisochny artery and vein and hemorrhage to the macular area: fig. 7 — an eyeground before treatment (visual acuity — 0,1); fig. 8 — an eyeground after laser therapy; vessels of a koagulirovana (visual acuity — 0,8).
Fig. 9. An eyeground in the remote terms after a pan-retinal lazerkoagulyation concerning thrombosis of the central vein of a retina (visual acuity — 0,8).

2. Fibrinferments of retinal vessels (especially veins) also became available direct to lay down. to influence only with L. Lazerkoagulyation's use promotes activation of blood circulation and oxygenation in a retina, to reduction or elimination of trophic hypostasis of a retina which without to lay down. influences usually comes to the end with heavy irreversible changes (tsvetn. fig. 7 — 9).

3. The degeneration of a retina, especially in a stage of transudation, in some cases successfully gives in to a lazerterapiya, edges are represented by almost only way of active intervention in this patol, process.

4. Focal inflammatory processes on an eyeground, periphlebites, limited manifestations of an angiomatosis in some cases also successfully recover by means of a lazerterapiya.

Fig. 4 and 5. Puncture ruby lazer of a perednekamerny epithelial cyst of an iris of the eye: fig. 4 — a perednekamerny epithelial cyst of an iris of the eye (a blue spot at the left above); fig. 5 — an iris of the eye directly after a puncture a ruby lazer (the cyst is replaced with cicatricial fabric — at the left above).
Fig. 6. Area of a pupil after «laser discission» of a crystalline lens at a cataract: laser radiation led to a rassasyvaniye of lenticular masses.

5. Secondary cataracts and membranes in the field of a pupil, tumors and cysts of an iris of the eye thanks to L. for the first time became object of nonsurgical treatment (tsvetn. fig. 4 — 6).

Fig. 6. An eye after laser corectomy (the zone of corectomy is designated by an arrow).
Fig. 7. Scheme of a lazergoniopunktura: 1 — the gonioscopy lens sending a laser beam to an anterior chamber of an eye; 2 — a pupil; 3 — a cornea; 4 — an iris; 5 — a corner of an anterior chamber; 6 — a ciliary body; 7 — a crystalline lens; the arrow showed the direction of a laser beam.
Fig. 3. Trabekulopunktura a ruby lazer at an open angle glaucoma.

6. At uzkougolny to glaucoma (see). L. for the first time instead of a classical method of the choice corectomies (see) allowed to carry out nonsurgical corectomies» and by that to turn surgery into the out-patient procedure. Sovr, techniques of laser corectomy, in particular developed in the USSR by M. M. Krasnov with soavt, a method of two-stage corectomy by means of two L., allow to reach corectomy almost at 100% of sick (fig. 6); its hypotensive effect (as well as at surgical intervention) considerably depends on timeliness of the procedure (in late stages in a corner of an anterior chamber commissures — the so-called goniosinekhiya demanding additional corrective actions develop). At a so-called open angle glaucoma by means of a method of a lazergoniopunktura it is possible to avoid operational treatment approximately at 60% of patients (fig. 7 and tsvetn. fig. 3); for this purpose in the Soviet Union for the first time in the world the basic equipment of a lazergoniopunktura by means of modulated pulse («cold») L. Vozmozhna also a lazerkoagulyation of a ciliary body for decrease in intraocular pressure due to reduction of products of intraocular liquid is developed. Favorable action of L is proved. on the course of virus processes in a cornea, especially on some forms of a herpetic keratitis which treatment represented a difficult problem.

With the advent of new types L. and new techniques of its use on an eye of a possibility of laser therapy and laser microsurgery in ophthalmology constantly extend. In connection with comparative novelty of laser methods character of the long-term results of treatment of a number of diseases (diabetic damages of eyes, inflammatory and dystrophic processes in a retina, etc.) needs further specification.

From additional materials

the Laser in treatment of glaucoma. The purpose of laser influence at glaucoma (see) is normalization of intraocular pressure (see). The essence and the mechanism of hypotensive action of laser radiation can be various depending on a form of glaucoma and features of the used laser source. The greatest distribution to Ophthalmolum. to practice received argon lasers of continuous action and pulse laser sources on a ruby and yttrium-alyuminiye-vom to the grenade. In a laser source on a ruby the active environment is the crystal of a ruby enriched with trivalent ions of chrome (A1203:

Sg3+), and in a laser source on yttrium - aluminum garnet —

a crystal yttrium - aluminum garnet, activated by trivalent ions of neodymium (Y3A15012:


At closed-angle glaucoma by means of the laser create a through hole in an iris of the affected eye (a laser iridotomy) therefore outflow of intraocular liquid improves.

As the indication to a laser iridotomy serve periodically repeating bad attacks of increase in intraocular pressure with its datum level in the mezhpristupny period, and also continuous increase in intraocular pressure in the absence of sinekhialny changes in a corner of an anterior chamber of an eye; apply three kinds of a laser iridotomy: the layer-by-layer, single-step and combined laser iridotomy. At all three methods of laser influence choose the most thinned site in a stroma of peripheral department of an iris (see).

The layer-by-layer laser iridotomy is carried out by means of the argon laser. At the same time consistently put impulses in one point that leads to gradual formation of deepening in a stroma of an iris, and then — a through hole. In the course of treatment carry out

from 1 to 4 sessions. For performance of a single-step laser iridotomy use the short-pulse laser. At one application of the focused laser impulse on a surface of an iris the through hole is formed (see the Coloboma). The combined laser iridotomy combines elements of a layer-by-layer and single-step iridotomy and is carried out in two stages. At the first stage make coagulation of an iris the radiation of the argon laser for the purpose of formation during the subsequent 2 — 3 weeks of the site of an atrophy and thinning of a stroma. At the second stage carry out single-pulse perforation of an iris the radiation of the short-pulse laser.

At an open angle glaucoma by means of the laser recover permeability of the struck drainage system; at the same time use a laser goniopuncture (create artificial openings in trabeculas and an internal wall a helmet mova of the channel) and a laser trabeku-loplastika — coagulation of trabeculas or the forefront of a ciliary (ciliary) body that leads to a tension of trabeculas and expansion of inter-trabecular spaces. Treatment by the laser is shown in cases of inefficiency of medicamentous therapy or intolerance of the applied pharmaceuticals, during the progressing of a disease.

At a laser goniopuncture as a laser source use the short-pulse laser. Consistently put 15 — 20 laser impulses in one row focused on a surface of trabeculas in a projection of a shlemmov of the channel; intervention is carried out in the lower half of a corner of an anterior chamber of an eye.

At a laser trabekuloplastika as a laser source use the argon laser. On all circle of a shlemmov of the channel put from 80 to 120 impulses in the form of the dot line on border between the shlemmovy channel and a front boundary ring of Shvalbe (see Gonioskopiya) or two parallel rows on the forefront of a ciliary body (laser trabekulo-spazis).

Can be complications of laser treatment of glaucoma slight bleeding from the vessels of an iris destroyed by a laser impulse; a long slow iritis (see the Iridocyclitis) without explicit a wedge, manifestations, with education in late terms of plane back synechias; the reactive increase in intraocular pressure developing after an incomplete laser iridotomy; damage of an endothelium of a cornea is in rare instances observed (see) laser radiation at indistinct focusing of a laser bunch on a surface of an iris. Observance of necessary preventive measures (a right choice of the place of influence and the correct technical performance of a method) does the frequency of these complications minimum.

The forecast at laser treatment of glaucoma favorable especially in an initial stage of a disease: normalization of intraocular pressure and stabilization of visual functions is in most cases observed.

See also Glaucoma.

Laser photocoagulation in treatment of a diabetic retinopathy. Conservative methods of treatment of a diabetic retinopathy (see) are ineffective. In treatment of this disease in the last decade actively use the laser. Laser photocoagulation of extensive sites of an ischemic retina leads to its destruction and the termination of growth of neogenic vessels.

Laser photocoagulation at patients with a diabetic retinopathy is shown at emergence of the first symptoms of ischemia of a retina revealed by method of a fluorescent angiography (see): patol. to a pronitsaa

bridge of retinal capillaries; emergence of the not perfusing sites of a retina located outside area of a macula lutea; for the first time the found signs of a neovaskulya-rization on an optic disk and on the course of the main branches of the central arteries and veins of a retina. In later stages of process which are characterized by the expressed glial proliferation, laser photocoagulation is contraindicated. For treatment of a diabetic retinopathy the most widespread laser source is the argon laser photocoagulator. Pan-retinal laser photocoagulation is considered an optimum technique, at a cut of coagulation subject the big surface area of a retina — from the central departments to the equator, and if necessary and the extreme periphery. Intact keep only macular area with a papillomakulyar-ny bunch and an optic disk. Ikhmpulsa put bucketed, equal to a half of diameter of a laser spot. Normal vessels of a retina do not coagulate. In process of removal from the center of an eyeground to the periphery diameter of a focal spot of a laser beam is increased. Pan-retinal photocoagulation is carried out in 3 — 4 sessions with intervals between them from 2 to 7 days. Total number of laser coagulations for one eye can reach 2000 — 2500. Perhaps also use of direct coagulating laser impact on neogenic vessels — direct focal laser photocoagulation. Bunches of neogenic vessels coagulate by drawing on them a large number of impulses before complete cessation of a blood-groove in them.

Quite often combine pan-retinal and focal laser photocoagulation.

The most widespread complication of laser treatment of a diabetic retinopathy (to 10% of cases) are retinal apoplexies (see) and a vitreous (see) — a partial or full hemophthalmia (see), burdening the course of a diabetic retinopathy, reducing visual acuity and complicating further use of laser photocoagulation. The reactive hypostasis of macular area of a retina or development of her acute ischemia, wrinkling of a vitreous (owing to its excess heating) leading to irreversible decrease in visual acuity is possible.

Prevention of the described complications of laser photocoagulation consists in a right choice of indications, careful observance of the equipment of a method. During the performance of these conditions laser photocoagulation more than at a half of patients with a diabetic retinopathy leads to permanent improvement.

See also diabetes mellitus.

Bibliograkopyan V. S. Laser methods of treatment of primary glaucomas, Vestn. oftalm., No. 6, page 19, 1982; Acre

pyan V. S. and Drozdov H. M. Medical and preventive value of laser corectomy in clinic of primary angular glaucoma, in the same place, No. 1, page 10, 1977; they, Single-pulse laser corectomy, in the same place, No. 4 of page 15, 1981; Krasnov M. M. Laser microsurgery of an eye, in the same place, No. 1, page 3, 1973; Krasnov of M. M. Lazeropunktur of a corner of an anterior chamber at glaucoma, in the same place, No. 3, page 27, 1972; about N e, Microsurgery of glaucomas, M., 1980;

Krasnov M. M., etc. Laser treatment of primary open angle glaucoma, Vestn. oftalm., No. 5, page 18, 1982; Bass M. S., Perkins E. S. a. Wheeler of Page B. Experimental results with a pulsed dye laser, Advanc. Ophthal., v. 34, p. 164, 1977; Bass M. S. a. o. Single treatment laser iridotomy, Brit, J. Ophthal., v. 63, p. 29, 1979; Diabetic retinopathy study. Sixth and seventh reports from the diabetic retinopathy study,

Invest. Ophthal. Vis. Sci., v. 21, N 1, pt 2, 1981; The diabetic retinopathy study research group, Photocoagulation treatment of proLiferative diabetic retinopathy, Ophthalmology, v. 85, p. 82, 1978;

The diabetic retinopathy study research group, Preliminary report on effects of photocoagulation therapy, Amer. J. Ophthal., v. 81, p. 383, 1976; Hager H.

Besondere mikrochirurgische Eingriffe, 2. Etst Er-fahrungen mitdem Argon-Laser-Gerat 800, Klin. We. Augenheilk., Bd 162, S. 437, 1973; L’Esperance F. A. a. James W. A. Diabetic retinopathy, clinical evaluation and management, St Louis, 1981; Perkins E. S. Laser iridotomy, Brit. med. J., v. 1, p. 580, 1970; Perkins E. S. a. Brown N. W. A. Iridotomy with a ruby laser, Brit. J. Ophthal., v. 57, p. 487, 1973; Wise J. B, Glaucoma treatment by trabecular tightening with argon laser, Int. ophthal. Clin., v. 21, p. 69, 1981; W about

r-the n D. M. a. Wickham M. G. Argon laser trabeculotomy, Trans. Amer. Acad. Ophthal. Otolaryng., v. 78, p.

371, 1974. V. S. Akopyan.

Lasers in stomatology

Experimental and theoretical justification of use of L. in stomatology researches of features of the mechanism of influence of radiations of various types L were. on teeth (see. Teeth, damages ), jaws and mucous membrane of an oral cavity.

Diagnosis of diseases of teeth and jaws by means of L. has considerable advantages in comparison with a X-ray analysis. L. use for transillumination (raying) by means of flexible fiber glass light guides for detection of microcracks of enamel of teeth (including on proximal hardly accessible surfaces of crowns of teeth), a subdingival dental calculus, definition of a condition of a pulp of tooth (denticles, mummification, a necrosis, etc.), a condition of roots of milk teeth, rudiments of crowns and roots of second teeth at children. Laser light sources apply in photo-pletizmografii (see. Pletizmografiya ), for diagnosis of diseases of a pulp of tooth, a parodont and jaws. The laser holography is carried out for diagnosis and assessment of efficiency of treatment of the inborn and acquired deformations of the person and in funkts, diagnosis stomatol, diseases, for interpretation and the analysis reogramm, polyarogramm, photoplethysmograms, miogramm, etc.

Prevention of initial stages of caries and not carious damages of teeth (erosion, wedge-shaped defects, etc.) carry out by «glazing» of the damaged sites of enamel of tooth in garnet, carbon dioxide and other L., working in the mode of modulation of the good quality of radiation (low power in an impulse and the high frequency of impulses) allowing to avoid an adverse effect of high temperatures on a pulp of tooth, crazing of enamel and dentine. Same L. use for a provarivaniye of seams between a seal and enamel of tooth that warns a recurrence of caries, and ultra-violet L. — for hardening of sialant (adhesives) at a covering of fissures of chewing teeth at children.

At interventions on jaws (cutting of a bone, windowing, a compact osteotomy, imposing of bone seams on fragments of jaws at their changes, an osteolasty, etc.) apply garnet, carbon dioxide and other L. S the help of the same L. prepare teeth, carry out the emergency opening of a pulp cavity at pulpitises, periodontitis operations of a radectomy, vesicotomy and a cystectomy, a maxillary sinusotomy, an alveolotomiya, a resection of jaws concerning bone, napr, adamantinomas, odontomas, and other tumors of jaws. For operations on soft tissues, including at plastics of a red border of lips and face skin, at operational treatment of diseases of sialadens, hemangiomas and other tumors of maxillofacial area use laser «scalpel».

Most in stomatology were widely adopted highly effective helium - neon L. for treatment of inflammatory diseases of a mucous membrane of an oral cavity (herpetic and hron, recurrent aphthous stomatitis, herpes of lips, a glossodynia, a glossitis, red flat depriving, a mnogoformny exudative erythema, Melkersson's syndrome — Rosenthal, etc.). periodontosis. It is noted that laser radiation is followed by stimulation of healing of postoperative wounds, burns of a mucous membrane of an oral cavity and face skin, trophic ulcers of an oral cavity, etc.

Complications. Laser radiation at the wrong and careless use it can do big harm to both the patient, and medical staff — to cause hemorrhage from vessels, to lead to a burn of eyes, a necrosis, damage of bones, vessels, parenchymatous bodies, blood and closed glands. Prevention of complications in many respects depends on the correct possession of a technique of treatment, selection of patients and an optimal variant of the technology of treatment.

Occupational health during the work with lasers

the Hygienic characteristic of the production factors accompanying operation of laser machines.

Kliniko-gigiyenichesky and pilot studies showed that laser radiation is among biologically active physical. factors can also constitute danger to the person. This circumstance defines need of development of actions for occupational health and the accident prevention during the work with laser machines and the organizations current and precautionary a dignity. supervision of their implementation and operation.

In the mechanism biol, actions of H.p. as continuous radiation on the first place thermal effect acts. In process of shortening of an impulse and increase in power of radiation value of mechanical effect increases. The pilot studies concerning the mechanism of action showed that biol, the effect depends on the wavelength of radiation, energy, duration of an impulse, frequency of following of impulses, character of radiation (direct, specularly or diffuzno reflected), and also from anatomo-fiziol, features of the irradiated object.

At action of laser radiations of rather big intensity along with morfol, shifts of reflex character arise changes of fabrics directly in the place of radiation various funkts. It is established also that at the persons servicing laser machines at influence of laser radiations of small intensity develop funkts, changes in c. N of page, cardiovascular, endocrine systems, in the visual analyzer. Experimental data and observations in public demonstrate that funkts, shifts at the same time can have the expressed character and lead to disturbance of health. Therefore gigabyte. actions shall consider an opportunity not only the damaging action of laser energy, but also to recognize that this factor is an inadequate irritant for an organism even at small intensivnost. As showed I. R. Petrov's works, A. I. Semenova, etc., biol, effect of influence of laser radiation can amplify at repeated influences and at a combination with other factors of the production environment.

Direct contact of medical staff with L. is periodic and makes from 3 to 40 hours a week. During the performance of additional experimental works operating time with L. can increase twice. The engineers and technicians who are engaged in setup and an adjustment of L., can be exposed to direct action of direct laser radiation. Doctors and nurses are affected by the radiation reflected from fabrics. Levels of radiation in workplaces of medical staff can make 4*10 - 4 — 1*10 - 5 W/cm 2 also depend on reflective abilities of the irradiated fabrics.

At use helium - neon H.p. a power output 40 — 50 mt power flux density in workplaces of personnel can make 1,5*10 - 4 — 2,2*10 - 4 W/cm 2 . At a power output of lasers 10 — 25 mt power flux density decreases on 2 — 3 orders. At production of diamond dragged and to a punched hole of openings in hour stones by means of neodymium H.p. energy in an impulse to 8 — 10 J the flux density of energy at the level of eyes of workers makes 3*10 - 4 — 3*10 - 5 J/cm 2 and 5*10 - 5 — 2*10 - 6 J/cm 2 . High densities of energy diffuzno of the reflected radiation can be created in workplaces at use of powerful carbon dioxide L. for cutting of a steel sheet, cutting of fabrics, skin and so forth.

In addition to possible adverse action direct, specularly or diffuzno the reflected laser radiation, the light energy from flashlight valves of a rating reaching in some cases 20 kJ can exert an adverse effect on function of sight of working. At the same time brightness of flash of a xenon lamp makes apprx. 4*10 8 nt (cd/m 2 ) lasting impulse of 1 — 90 ms. Influence of radiation of lamps of a rating is possible at their time shielding or at an insufficient ekranirovka, hl. obr. during the testing of a duty of flashlight valves. Cases of the spontaneous category of razekranirovanny lamps since at the same time the personnel do not manage to take precautionary measures are the most dangerous. At the same time perhaps not only the disturbance of visual adaptation remaining within several minutes but also organic lesions of various departments of an eye. Subjectively the category of a razekranirovanny lamp is perceived as «an intolerable slepimost». The radiation spectrum of flashlight valves contains also long-wave UV rays which can affect personnel only during the work with open or insufficiently screened flashlight valves, causing additional, specific, reaction of an eye.

It is also necessary to pay attention to a number of the nonspecific factors accompanying work with the laser. Because laser radiation constitutes the greatest danger to eyes, special attention should be paid on illumination of jobs and rooms. Kind of work with L., as a rule, demands big visual tension. Besides, in the conditions of low illumination biol, the effect of impact of laser radiation on a retina amplifies since at the same time the area of a pupil of an eye and sensitivity of a retina will significantly increase. All this dictates need of creation enough high levels of lighting of production rooms during the work with L.

Operation of laser machines can be followed by noise. Against the background of the stable noise reaching 70 — 80 dB sound impulses in the form of cottons or clicks due to impact of a laser beam on the processed material or due to work of the mechanical locks limiting duration of an impulse of radiation take place. During the working day the amount of cottons or clicks can reach many hundreds and even thousands, and levels of the volume of 100 — 120 dB. Categories of flashlight valves of a rating, and also, perhaps, and process of interaction of a laser beam with the processed material (a plasma torch) are followed by formation of ozone, contents to-rogo can vary over a wide range.

Clinical manifestations of the general influence of laser beams. In a problem of providing safe working conditions with L. a specific place is held by an organ of sight. Transparent environments of an eye freely pass radiations of the optical range including a visible part of a range and near area of infrared radiation (0,4 — 1,4 microns) and focus them on an eyeground owing to what energy density on it increases many times over. Weight of injury of a retina and a choroid depends on parameters of radiation. Expressiveness patomorfol. changes and the wedge, a picture of disorders of function of sight can be various — from insignificant funkts, the changes revealed instrumentalno before total loss of sight. The most typical damage are chorioretinal burns. Patol, changes in front departments of an eye can arise at more considerable levels of energy of laser radiation. Emergence of similar pathology at use of L. in technology and in medicine it is practically excluded. However in connection with growth of power of L. and development of new ranges of radiations (ultra-violet, infrared) the probability of damage of front departments of an eye increases.

Burns of skin can arise at influence of big levels of energy of laser radiation, about several J/cm2. The available data demonstrate that at impact on skin of laser radiation of small intensity in an organism there are the general funkts, and biochemical, changes.

At accidental radiation of eyes and skin laser energy of big density the victim shall see immediately a doctor for diagnosis of defeat and rendering medical aid. The principles of first-aid treatment in these cases same, as well as at burns of eyes and skin of other etiology (see. Eye, burns ; Burns ).

Preventive actions against defeat by laser beams

Protective and a gigabyte. actions for prevention of adverse action of radiations of L. and other concurrent factors shall include actions of collective character: organizational, technical. planning, sanitary and hygienic and also to provide individual means of protection.

The requirement of assessment before operation of the laser machine of the major adverse factors and features of distribution of laser radiation is obligatory (both direct, and reflected). By tool measurement (as a last resort in the settlement way) levels of radiation determine the probable directions and sites on which are possible dangerous to an organism (exceed PDU).

For providing safe working conditions, in addition to strict observance of collective actions, use of individual protection equipment — the points, guards, masks having the spectral and selection transparency, and special protective clothes is recommended. An example of domestic safety spectacles from laser radiations in a spectral range with the wavelength of 0,63 — 1,5 microns are the points made of blue-green SZS-22 glass, providing protection of eyes against radiations of ruby and neodymium L. During the work with powerful L. protective guards and masks are more effective, gloves from suede or skin are put on hands. Carrying aprons and dressing gowns of various flowers is recommended. The choice of means of protection shall be made individually in each case by qualified specialists.

Medical overseeing working with the laser. The works connected with service of laser machines are included in lists of works with harmful working conditions, and working are subject to medical examinations preliminary and periodic (once a year). In surveys participation of the oculist, therapist, neuropathologist is obligatory. At a research of an organ of sight apply a slit lamp.

In addition to medical inspection, carry out a wedge, blood test with definition of hemoglobin, erythrocytes, reticulocytes, thrombocytes, leukocytes and ROE.

Bibliography: Alexandrov M. T. Use of lasers in experimental and clinical stomatology, the Medical paper. zhurn., section 12 — Stomatology, No. 1, page 7, 1978, bibliogr.; Gamaley N. F. Lasers in an experiment and clinic, M., 1972, bibliogr.; Kavetskiyr. E., etc. Lasers in biology and medicine, Kiev, 1969; To about r y t of N y y D. L. Laser therapy and its use in stomatology, Alma-Ata, 1979; Krasnov M. M. Laser microsurgery of an eye, Vestn, oftalm., No. 1, page 3, 1973, bibliogr.; Lazarev I. R. Lasers in oncology, Kiev, 1977, bibliogr.; Osipov G. I. and Pyatin M. M. Injury of an eye by a laser beam, Vestn, oftalm., No. 1, page 50, 1978; P l of e of t of N of e in S. D., etc. Gas lasers in experimental and clinical oncology, M., 1978; P r about-honchukov A. A. Achievements of quantum electronics in experimental and clinical stomatology, Stomatology, t. 56, No. 5, page 21, 1977, bibliogr.; Semenov A. I. Influence of radiations of lasers on an organism and measures of prevention, Gigabyte. work and the prof. having got sick., No. 8, page 1, 1976; Means and methods of quantum electronics in medicine, under the editorship of R. I. Utyamy-shev, page 254, Saratov, 1976; Khromov B. M. Lasers in experimental surgery, L., 1973, bibliogr.; Khromov B. M., etc. Laser therapy of surgical diseases, Vestn, hir., No. 2, page 31, 1979; L’Esperance F. A. Ocular photocoagulation, stereoscopic atlas, St Louis, 1975; Laser applications in medicine and biology, ed. by M. L. Wolbarsht,< v i — z? N. Y. — L., 1971 — 1977, bibliogr.

V. A. Polyakov; V. I. Belkevich (tekhn.), H. F. Gamaley (PMC.), M. M. Krasnov (oft.), Yu. P. Paltsev (gigabyte), A. A. Prokhon-chukov (ostomies.), V. I. Struchkov (hir.).