Laser damage to human eyes and skin

by:LASERRPAIR     2020-06-06
??????The application of laser in medicine has been expanded, and the field of application continues to expand. If you do not pay attention to the safety protection of the laser during the application process, it may cause accidental injuries. Accidents in clinical applications have been reported. While giving full play to and using the laser, safety protection must be carried out. First, laser damage to the eyes Laser wavelength and eye damage: Among the laser damage, the eye damage in the body is the most serious. Lasers with wavelengths in visible light and near-infrared light have a low absorption rate and high transmittance of the refractive medium of the eye, and the focusing ability (ie, light-gathering power) of the refractive medium is strong. When high-intensity visible or near-infrared light enters the eye, it can pass through the refractive medium of the human eye and accumulate light on the retina. At this time, the laser energy density and power density on the retina are increased to thousands or even tens of thousands of times. And lose the role of light. The coagulation and denaturation of proteins caused by overheating when the laser converges on the photoreceptor cells is irreversible damage. Once damaged, it can cause permanent blindness of the eyes. Different laser wavelengths have different effects on the eyeball, and the consequences are also different. The damage of the far infrared laser to the eye is mainly cornea. This is because the laser of this wavelength is almost completely absorbed by the cornea, so the corneal damage is the most serious, mainly causing keratitis and conjunctivitis. Fear of light, tearing, hyperemia of eyes, decreased vision, etc. In case of far-infrared light damage, the injured eye should be covered and protected to prevent infection and symptomatic treatment. Ultraviolet laser damage to the eye is mainly the cornea and the lens. Almost all the ultraviolet laser in this band is absorbed by the lens of the eye, while COSCO mainly absorbs the cornea, which can cause the lens and cornea to be cloudy. Second, the relationship between incident laser intensity and eye damage The degree of laser damage to the eyes is not only related to lasers of different wavelengths (CO2 laser 10.6 μm; Nd: Yag laser 1.06 μm, He-Ne laser 632.8 nm), but also related to the total light energy, energy density and power density of the laser entering the eye United. Among the types of lasers, when the visible or near-infrared laser power density is very low, it does not cause acute eye damage. The main reason is that due to the low power density of the laser, the retinal tissue gradually heats up after receiving the laser photon energy, but on the one hand, the heat is transferred to the surrounding tissue through molecular vibrations, and then to the outside of the eye; on the other hand, the heat can be transferred Give the microvessels densely packed in the choroid of the bottom of the omentum, and then circulate outside the eye as the blood circulates in the microvessels. Therefore, the temperature of the retina to the whole eye does not increase significantly, or slightly changes in temperature, and it is still in a range that is completely harmless to the eye. The damage to the retina depends on the power and time. For example, when the power density of the visible or near-infrared continuous laser is increasing, the heat accumulation speed on the retina is greater than the heat dissipation speed, or the power density is not very high, but the retina absorption time is too long. The temperature of the part where the retina receives photon flow must rise, that is, the longer the irradiation time, the greater the temperature rise, and the greater the temperature rise. If it exceeds the normal eye temperature by more than 10 ° C, it will cause retinal damage. 1. Pupil size and degree of damage pupil size has a certain proportional relationship with the degree of injury. A reduced pupil can reduce the amount of laser light entering the fundus. The larger the pupil, the greater the amount of laser light entering the eye, and the greater the degree of fundus damage, the more irreversible. Therefore, pupil reduction has certain significance for protecting the fundus retina and preventing laser beam damage. 2. The change of the pupil is different from the environment. In a dark room, the pupils are spread apart. In debugging in such an environment, those who use lasers must carefully protect their eyes. Therefore, when the pupil of the eye is outside the maximum state, although the amount of light entering is small, it is also the easiest to damage the retina of the eye. In addition to reducing the amount of light entering the pupil, the amount of laser light outside the pupil can be absorbed by the iris, and the heat can be diffused and transferred by the microvessels of the iris. The eyes of the average person, when adapting to a dark environment, have a pupil diameter of 7 to 8 mm, which can be reduced to only 1.5 mm under visible strong light, and usually have a pupil diameter of about 2 to 3 mm during the day. Therefore, the light transmission area between the largest pupil and the smallest pupil differs by more than 20 times. 3. The incidence angle of laser in eye injury Due to the special anatomy and special physiological relationship of the eyeball, laser damage to the retina is closely related to the angle of the incident eye. The reason is that the eyeball itself is a condenser lens system. When the incident laser beam enters the eye parallel to the visual axis, it is focused into a small spot in the central fovea of ??the fundus macular area, and its energy density is 3 to 4 times higher than that of the cornea . The fovea of ??the macular area is the most sensitive and important area of ??the visual function of the eye. Once damaged, the visual function will change to varying degrees. In severe cases, you will be blind for life. Because the damage of vision is caused by laser photons, the photoreceptor cells are degenerated and necrotic, causing irreversible damage. During the day, the color vision of the human eye is completely obtained by the photosensitization of the macula. Although the area of ??the macula only accounts for a small part of the total area of ??the retina, the diameter of the fovea is only about 0.5mm. But the reflected field of view (the total area that the eyes can see clearly in front of the gaze) accounts for a large proportion. On the physiological structure, the central fovea of ??the macula is composed of 20,000 to 30,000 long and thin pyramidal photoreceptor cells. The distribution density of photoreceptor cells is very high, mainly responsible for visual functions. The visual function of daylight is lost after being injured. In addition, there is no blood vessel and nerve distribution in the central fovea of ??the retina, so the heat diffusion function of this part is very poor. Once the injury, the hope of repair is very slim. The fovea is the weakest part of the retina. It is more likely to be damaged than other parts of the retina after being exposed to laser light, so direct laser light is very dangerous. When the laser light enters the eye slightly away from the visual axis, the focused spot will not fall on the macular area, but on the peripheral retina. Therefore, if the incident angle is different, the damage will be different. Even if the energy entering the eye is the same as that under direct irradiation, the damage caused is much lighter. The reason is that the photoreceptor cells on the site other than the macula are much less densely distributed than the macular area, and the retina outside the macula is thicker, receives the same energy per unit area, and its temperature rise is much smaller. In addition, the retina outside the macular area is densely covered with microvessels, and some heat can be taken away from the blood circulation, which reduces the possibility of temperature increase. The higher the temperature, the heavier the damage; conversely, the smaller the temperature increase, the less likely the damage. The main effect of laser on the acute damage to the retina is caused by thermal effects. The incident angle of the laser is not synchronized with the visual axis. The larger the deviation angle, the less damage to the retina. The iris can block the deviated laser without entering the fundus. Because the central fovea of ??the macula plays a very important role in visual function, and this part is most susceptible to damage, the danger of looking directly at the laser beam is much greater than that of entering the eye at an angle off the visual axis. Must be absolutely avoided. Fourth, fundus pigment content and damage relationship There is a specific relationship between the amount of pigment in the fundus and the degree of laser damage. Pigment tissue is very easy to absorb laser energy, so the amount of pigment directly affects the laser's moderate damage to the retina. It is reported in the literature that there is a positive correlation between the skin tone of the body and the pigments in the fundus. Those with heavy black skin have more pigments in the fundus; those with white skin have less pigments in the fundus. Therefore, the more pigment content, the stronger the absorption of laser light, the greater the degree of damage. The eye tissue will be injured after absorbing energy exceeding its own injury threshold. The more you exceed, the more damage you will receive. V. Laser damage to the skin Due to the physiological structure, human skin has very sensitive functions such as touch, pain and temperature, which constitute a complete protective layer. And the skin is composed of multiple tissue layers, with different cells in each layer. When the laser shines on the skin, if the energy (power) is too large, it can cause skin damage. Of course, the lesion can be repaired by tissues. Although the function is reduced, it does not affect the overall functional structure, and the damage to the eyes is much lighter. . But it must also be highly valued. The threshold of laser damage to the skin is also very high, the output energy of various lasers varies greatly, and the range of high-power lasers currently used is very wide. The degree of laser damage to the skin is related to factors such as the dose of the laser, the wavelength of the laser, the skin tone, the moisture of the tissue, and the thickness of the cuticle of the skin. The previous three factors are the main factors. Laser dose and degree of skin damage: After a lot of practice, the greater the laser power density (or energy density) used when irradiating the skin, the greater the damage to the skin, and the two are positively related. After the skin absorbs laser energy that exceeds the safety threshold, the skin on the exposed area will appear thermally induced erythema, blisters, coagulation and thermally induced carbonization, boiling, combustion and thermally induced vaporization with increasing dose. Therefore, the mechanism of laser damage to the skin is mainly caused by the thermal effect of the laser. After the skin absorbs laser energy, the local skin temperature rises within a short period of time, and the degree of temperature rise is different, causing different damage. In particular, infrared lasers are prominent, such as CO2 lasers (vapor lasers). The skin has a high absorption rate of 10.6 μm wavelength infrared lasers and low transmittance. The skin absorbs CO2 lasers strongly, causing the local temperature of the skin to rise rapidly. High, very easy to cause damage. The severity of laser damage to the skin is determined by the skin's absorption rate of the laser, and the skin's absorption rate of the laser is determined by the wavelength of the laser. The higher the skin's absorption rate of a certain wavelength of laser, the more serious the damage will be. For example, when the skin's absorption rate of ultraviolet laser and infrared laser is very high, these two types of lasers are the main band lasers that damage the skin. The main effect of infrared laser on the skin is thermal burns. This kind of laser irradiates the skin, and the power is relatively small, causing the capillaries to dilate, and the skin is red and fever. As the laser power density increases, the degree of thermal damage also increases. On the contrary, the effect of ultraviolet laser on the skin is mainly light. When irradiated with ultraviolet laser light on the skin, it can cause skin erythema and aging, and can cause severe carcinogenesis when overdose. Ultraviolet light waves that are most harmful to the skin are between 270 and 290 nm, and wavelengths larger or smaller than 270 to 290 nm are relatively less harmful. VI. Skin color and laser damage The darker the color of the skin, the more melanin particles the cells in the skin contain. The pigment particles can convert laser energy of various wavelengths into thermal energy. After absorbing the laser energy, a local heat source is formed and quickly spreads around Heat energy, which causes cell and tissue destruction and death. The more melanin particles contained in the skin, the more heat sources will be formed, and the higher the efficiency of converting light energy into heat energy, resulting in a greater protein coagulation denaturation rate and greater cell death rate. The lighter the skin, the lighter the damage.
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