Although lasers have been commonly used in all aspects of medicine, they are most widely and deeply used in the field of ophthalmology. This is because the eye itself is an optical system, light can reach all layers of the eye through the refractive interstitium, because the laser has the advantages of consistency of wavelength, good directionality, etc., can be applied to different wavelengths of laser, targeting different tissues of the eye accurately to play a role, so in the field of medicine first applied to ophthalmology, and the widest range, has formed a subdiscipline of laser medicine -Laser ophthalmology. I, laser treatment of eye diseases 1, the role of different wavelengths of laser on eye tissue Different parts of the eye tissue, due to the different pigments contained, there are significant differences in the absorption of different wavelengths of laser, the choice of laser treatment, the first consideration should be that the laser has a high absorption rate in its target tissue, and the path it passes through the refractive interstitial and other tissues on its absorption the less the better. In general, melanin has a higher absorption rate for shorter wavelengths of light, but the difference is not great; oxygenated hemoglobin has a high absorption rate for blue, green and yellow light, while it basically does not absorb red light and infrared light; lutein has a high absorption rate for blue light. Therefore, blue, green and yellow light are commonly used in iris, atrial angle tissue, retinal pigment epithelium and neovascular membrane, among which blue light can be absorbed by lutein, so it cannot be used in macular area to avoid damage to retinal neuroepithelium; red light and infrared light can only depend on melanin absorption, but can penetrate the thin bleb to reach the inner layer of choroid and retinal pigment epithelium, and is not absorbed by lutein, scattering less Therefore, it is often used for refractive interstitial unclear, retinal thin hemorrhage, macular area tissue, etc., but the effect is poor for non-pigmented or depigmented area, and it is easy to damage the deep fundus tissue due to strong penetration. Ultraviolet light with wavelength shorter than 295nm is mostly absorbed by corneal tissue and cannot reach intraocular tissue, so it is only used for corneal surgery at present. 2.The principle of laser treatment for eye diseases After the laser acts on the eye and is absorbed by the tissue, a series of changes will occur in the eye tissue, which is the basis of laser treatment. Photothermolysis is the process of converting light energy into heat after laser energy is absorbed by biological tissues, and is the most common method of laser treatment for eye diseases. The factors affecting the response level of ocular tissues are not only related to the laser power density, but also to the absorption rate of the corresponding wavelength of laser energy by the irradiated tissue and the duration of laser irradiation. Photothermolysis can also lead to secondary physicochemical reactions such as pressure and chemical effects. Photochemistry refers to the chemical reactions caused by the absorption of laser energy by biological tissues and the conversion of light energy into chemical energy. There are four main types: photolysis, photo-oxidation, photopolymerization and photosensitization. Photolysis and photosensitization are commonly seen in ophthalmic treatment. The former is the use of the ArF excimer laser with a wavelength of 193 nm as a “cold light knife” to break down the chemical bonds of biomolecules and “cut” the cornea. A typical example of the latter is the treatment of retinoblastoma with photodynamic therapy. Light is a changing electromagnetic wave, and a series of biological effects caused by the electromagnetic interaction between biological tissues and light wavelengths is called the electromagnetic field effect of light. Which is mainly strong electric field effect. For ordinary light, the biological effect of the electric field is not noticed because the optical power density is very low. But the laser makes the light energy is highly concentrated in space, such as the use of Q-switching, mode-locking and other technologies, but also make it highly concentrated in time, it can produce a considerable electric field strength, thus causing obvious biological effects. The laser with certain power density can also produce photopressure, which can be caused by various reasons, such as laser radiation, thermal vaporization recoil, thermal expansion, expansion ultrasound, field scattering and field stretching. This photopressure can act on the eye to produce biological effects. ⑤, vaporization, cutting, perforation principle High-power density continuous-wave laser acts on biological tissue and is absorbed by biological tissue to cause heat, and when the temperature reaches 100℃, the liquid in the tissue with water content of 60% to 80% begins to boil and vapor pressure appears, but because the surface is closed, as if it were a pressure cooker, when the laser energy is continuously absorbed, the temperature and air pressure in the tissue increase rapidly until it exceeds When the elastic limit of the sealed tissue is exceeded, steam is ejected through the surface, and the tissue fragments are also carried out by the airflow. The term “vaporization” generally refers to the cauterization of lesions and superfluous organisms, i.e., surface vaporization, which is called cutting if it is linear vaporization or perforation if it is punctiform vaporization. For specific tissues that absorb the appropriate energy, the depth at which vaporization is performed is in contrast to the duration and power density of the laser exposure. The cause of vaporization is mainly photothermal, but photochemical decomposition can also cut the tissue, while the penetrating cut used in ophthalmic treatment is more mainly due to the pressure effect or high electric field breakdown of the laser. The penetrating principle of pulsed laser can be due to photothermolysis, photocall field and photopressure. The Ar+ laser is used to penetrate the iris through the refractive mass and is absorbed by the pigment- and water-rich tissue, generating heat to the level of vaporization, and the resulting vaporization pressure causes micro-explosions in the tissue at the point of action, thus achieving the goal of “phototomy” of the iris. (7) Principle of coagulation After the laser irradiates biological tissues, it is mainly due to photothermolysis, which means that the biological tissues absorb the laser energy and convert the light energy into heat energy. Partly due to the photochemical effect, heat energy is generated, which causes damage to the irradiated tissue and leads to coagulation. Since the eye is a refractive system, most of the laser energy in the visible range can reach the fundus through the refractive interstitium and be absorbed by the pigmented tissues and oxidized hemoglobin in the fundus, resulting in photocoagulation and tissue mechanization and adhesions. Clinically, this coagulation and adhesion effect is used to close retinal fissures and lesions of blood vessels. 3, now the ophthalmology commonly used in the treatment of lasers in the field of medicine used in a very large variety of lasers, commonly used in ophthalmic treatment are mainly ruby (rudy) laser, argon ion (Ar +) laser, krypton ion (Kr +), dye (dye) laser, neodymium-doped yttrium aluminum garnet (Nd: YAG) laser and argon fluoride (ArF) excimer laser and other solid, gas and liquid lasers. Continuous, pulsed and Q-modulated modalities are used to treat dozens of related eye diseases in areas such as the uvea and refractive interstitium at the base of the eye. The ruby laser is a solid-state laser with a wavelength of 694.3 nm red visible light. It can be used for various types of fundus diseases such as retinal fissures, peripheral retinal degeneration, diabetic retinopathy, etc. The Q-modulated ruby laser can be used for phototomy, treatment of corneal scar clouding, pupil closure and atresia, pre-crystalline pigmentation, iris cysts, and peripheral iridotomy for closed-angle glaucoma. Because red light is not easily absorbed by oxidized hemoglobin, it is not as good as argon ion laser for the treatment of intraocular hemorrhage or vascular disease. Argon ion and krypton ion laser is two similar gas lasers, the former can produce continuous wavelength of 488.0 nm blue light and 514.5 nm green light, the latter can produce wavelength of 520.8 nm green light and 568.2 nm red light. Since all five spectral lines are strongly absorbed by pigmented tissues without damaging the refractive medium, which is transparent to visible light, they are suitable for all indications of the ruby laser. In particular, the blue and green light of the argon ion laser and the green and yellow light of the krypton ion laser are strongly absorbed by oxidized hemoglobin, so they can also be used to treat intraocular vascular and hemorrhagic diseases. Because the yellow and red light of the krypton ion laser is not absorbed by lutein, the damage to the upper retinal nerve layer is smaller, so it is better used to treat macular lesions. The red light can also penetrate the superficial retinal hemorrhage and act on the pigment epithelium, which cannot be replaced by other wavelength lasers. The main feature of the dye laser is that its output wavelength is continuously adjustable and can be either continuous or pulsed. At present, it is used to treat closed-angle glaucoma, secondary glaucoma, iris bulging, congenital pupillary residual membrane, etc. The wavelength of the dye laser is 585.0nm and 555.0nm. Because the wavelength of dye laser is difficult to be continuously adjustable in practical application, and the output is not very stable, the characteristics of continuously adjustable laser are not really played out at present, and there are not many clinical applications. The Nd:YAG laser has a wavelength of 1064 nm, which is an invisible infrared light that is not absorbed by the pigmented tissue in the eye, and is therefore used to treat lesions without pigmented tissue in the anterior segment of the eye. The Nd:YAG laser in Q modulation mode can concentrate a large amount of energy in a very short period of time and use photochemistry, photocall field, and photodischarge pressure to complete the transparent tissue transmutation. It is mainly used for cataract capsulotomy, peripheral iridotomy, vitreous mechanization strip release, etc. Because of its extremely short time, it does not produce thermal damage. There is also a frequency doubled Nd:YAG laser that changes the output wavelength to 532nm through crystal conversion. Because it is a solid-state laser, the stability is better than gas lasers, and the volume is small and light. Excimer laser is mainly used in ophthalmology clinic is the argon fluoride (ArF) laser, its output wavelength is 193nm far ultraviolet light, its biological should be mainly used in photochemical effect of photolysis, as a “cold knife” to break the bond of biological molecules. With this kind of knife to perform phototomy, its cutting accuracy can reach the μm level, and the damage range of the knife is only up to the nm level, and it will not damage the neighboring tissues because there is no thermal effect. Therefore, it is now used in corneal surgery, such as corneal refractive surgery, corneal scar removal, etc. Subepithelial excimer laser keratomileusis (Lasek) (l) Method 20% ethanol is used to infiltrate the marked area of corneal epithelial cells, the marked area is uncovered in a complete sheet, and the uncovered layer of corneal epithelial cells is reset after subepithelial excimer laser keratomileusis is performed. (2) Advantages Postoperative pain is less than PRK and recovery is faster. (3) The problems are not yet agreed, because the anterior elastic layer is ablated, other complications of PRK may still exist. Laser examination and diagnosis of eye diseases Laser is not only used for the treatment of eye diseases, but also plays a great role in the examination and diagnosis of eye diseases, such as refractive examinations using laser for optometry and multiple examinations; corneal topographer using laser for corneal refractive performance examination; and confocal laser fundus examination system, which includes confocal laser fundus tomography system, confocal laser Doppler fundus flowmetry, and confocal laser fundus imaging system, which are the most advanced fundus examination systems, and their roles are respectively: 1. Confocal laser fundus tomograph is the use of confocal laser scanning microscopy for ophthalmic diagnosis, and this technology enables ophthalmologists to accurately obtain topographic maps of different areas of the patient’s fundus, which are useful for optic nerve head analysis in Yukon eye diagnosis, examination of macular degeneration, retinal detachment It is particularly suitable for quantitative recording and analysis of changes in disease during treatment and for follow-up studies. 2.Confocal laser fundus imaging system The advanced confocal laser scanning technology is used to obtain digital angiographic images of sodium fluorescein and indole indocyanine green (ICG) alone or simultaneously, and they are high-quality three-dimensional real-time images with excellent quality of early and late fluorescein images. Confocal laser scanning technology ensures spatial and axial measurement accuracy. It detects and images light emitted in and around the plane of focus, while reflected or scattered light outside the focus is blocked and not detected. Therefore, this confocal technique has two outstanding advantages of acquiring three-dimensional imaging information and high resolution of imaging images. 3.Confocal laser Doppler fundus flowmetry It combines two complex detection methods – co-laser scanning laser Doppler flow – into one, which can non-invasively obtain the perfusion map of the retina or optic disc in the fundus. Two-dimensional scanning of the retina or optic disc is performed using an infrared laser. The optical Doppler effect refers to the change in frequency of the reflected and evanescent light produced by a moving object in response to irradiated light, and the interference of this frequency-changing reflected light with the opposing light from a stationary object, resulting in detectable transient light intensity changes