Although laser has been widely used in all aspects of the medical field, the application in the field of ophthalmology is the most extensive and in-depth. This is because the eyeball itself is an optical system, and the light can reach the various layers of the eyeball through the refractive interstitium. Due to the consistency of the wavelength and good directionality of the laser, lasers of different wavelengths can be applied, and the target can be accurately aimed at Different tissues of the eyeball play a role, so it is first used in ophthalmology in the medical field, and the X circumference is the most extensive, and has formed a branch of laser medicine – laser ophthalmology.

1. The effect of lasers of different wavelengths on eye tissue Different parts of the eye tissue have obvious differences in the absorption of lasers of different wavelengths due to different pigments. It has a high absorption rate, and the less it is absorbed by the refractive interstitium and other tissues on its path, the better. In general, melanin has a higher absorption rate for light with shorter wavelengths, but the difference is not very large; oxygenated hemoglobin has a high absorption rate for blue, green, and yellow light, but basically does not absorb red light and infrared light. ; Lutein has a higher absorption rate of blue light. Therefore, blue, green, and yellow light are often used in the iris, angle tissue, retinal pigment epithelium and neovascular membrane, etc. Among them, blue light can not be used in the macula because it can be absorbed in large quantities by lutein, so as to avoid damage to the retinal neuroepithelial layer. ; Although red and infrared light can only rely on the absorption of melanin, they can penetrate the thin hemorrhage to reach the inner layer of the choroid and the retinal pigment epithelium, and are not absorbed by lutein and have less scattering, so they are often used in the refractive chamber. The quality is not clear, the retina has thin hemorrhage, macular tissue, etc., but the effect on the non-pigmented or depigmented area is poor, and it is easy to damage the deep fundus tissue due to its strong penetration. Ultraviolet light with a wavelength shorter than 295 nm is mostly absorbed by the corneal tissue and cannot reach the intraocular tissue, so it is currently only used for corneal surgery.
2. The principle of laser treatment of eye diseases After the laser acts on the eyeball and is absorbed by the tissue, a series of changes will occur in the eyeball tissue, which is the basis of laser treatment. ①. Photothermal effect refers to the process that biological tissue absorbs laser energy and converts its light energy into heat energy. It is the most common method in laser treatment of eye diseases. Due to the difference in the level of local tissue response induced by heat, there are also a series of reactions such as thermally induced warming, coagulation, vaporization, perforation and cutting. It is related to the absorption rate of the laser energy of the corresponding wavelength and the duration of the laser irradiation. Photothermal effects can also lead to secondary physical and chemical reactions such as pressure and chemical effects. ②, Photochemical effect refers to the chemical reaction caused by biological tissue absorbing laser energy and converting light energy into chemical energy. There are four main types: photolysis, photooxidation, photopolymerization and photosensitization. Commonly seen in ophthalmic treatment are photolysis and photosensitization. In the former, the ArF excimer laser with a wavelength of 193 nm is used as a “cold light knife” to decompose the chemical bonds of biomolecules and “cut” the cornea. A typical example of the latter is the treatment of retinoblastoma with photodynamic therapy. ③、Electromagnetic field effect Light is a changing electromagnetic wave, and a series of biological effect processes caused by the electromagnetic interaction between biological tissue and light band are called electromagnetic field effect of light. The main one is the effect of strong electric field. For ordinary light, the biological effect of its electric field cannot be noticed due to the low optical power density. However, the laser makes the light energy highly concentrated in space, such as using Q-switching, mode-locking and other technologies, and making it highly concentrated in time, which can generate a considerable electric field intensity, thereby causing obvious biological effects. ④, Photo-induced pressure effect Laser with a certain power density can also produce photo-induced pressure effect, which can be caused by various reasons, such as laser radiation, thermally induced vaporization recoil, thermally induced expansion, expansion-induced ultrasound, field Caused by scattering, fieldstriction, etc. This light-induced pressure can act on the eye to produce biological effects. ⑤. Principle of vaporization, cutting and drilling High power density continuous wave laser acts on biological tissue, and is absorbed by biological tissue to cause heat. When the temperature reaches 100 °C, the water content of the tissue reaches 60% to 80%. The liquid begins to boil and steam pressure appears, but because the surface is closed, like a pressure cooker, when the laser energy is continuously absorbed, the temperature and air pressure in the tissue increase rapidly until the elastic limit of the sealed tissue is exceeded, and the steam breaks through the surface and sprays out. Tissue fragments are also carried out by the airflow. Generally speaking, “vaporization” refers to the cauterization of lesions and vegetations, that is, surface vaporization. If it is linear vaporization, it is called cutting, and if it is point vaporization, it is called perforation. For a specific tissue that absorbs the corresponding energy, the depth at which the vaporization takes place is compared to the time and power density of the laser irradiation. The main cause of vaporization is photothermal effect, but photochemical decomposition can also cut tissue, and the penetration of ophthalmic treatment is mainly due to pressure or high electric field breakdown of laser. ⑥. The principle of penetration The principle of penetration of pulsed laser can be due to the effect of photothermal heating, or it can be due to the effect of photoelectric field and photoinduced pressure. When using the Ar+ laser, it is used that it can penetrate the refractive quality to the iris, and is absorbed by this pigment and water-rich tissue, producing heat to the level of vaporization, and the resulting vaporization pressure causes the tissue at the point of action to form a micro-explosion. , so as to achieve the purpose of “light cutting” the iris. ⑦、Principle of coagulation After the laser is irradiated to the biological tissue, it is mainly due to the photothermal effect, that is, the biological tissue absorbs the laser energy and converts the light energy into heat energy. Part of it is due to photochemical action to generate thermal energy, which damages the irradiated tissue and causes coagulation. Since the eyeball is a refractive system, most of the laser energy in the visible X-ray range can reach the fundus through the eye refractive interstitium, and be absorbed by the fundus pigment tissue, oxidized hemoglobin, etc., thereby producing photocoagulation, and then forming tissue mechanization and adhesion. Clinically, this kind of coagulation and adhesion is used, and then it is used in the sealing of retinal breaks and the sealing of diseased blood vessels.
3. Lasers commonly used in ophthalmology treatment There are many types of lasers used in the medical field. The main ones commonly used in ophthalmology treatment are ruby (rudy) laser, argon ion (Ar+) laser, krypton ion (Kr+), dye (dye) Solid, gas and liquid lasers such as lasers, neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers, and argon fluoride (ArF) excimer lasers are used in continuous, pulsed and Q-switched methods to treat the pigmented membrane of the eye. Dozens of eye diseases related to the refractive interstitium and other parts. Ruby laser is a red visible light solid-state laser with a wavelength of 694.3nm. It can be used for various fundus diseases, such as retinal tears, peripheral retinal degeneration, diabetic retinopathy, etc. Q-switched ruby laser can perform light ablation to treat corneal cicatricial opacity, pupillary membrane closure and atresia, pre-lens pigment, iris cyst, and peripheral iridectomy for angle-closure glaucoma. Because red light is not easily absorbed by oxidized hemoglobin, the treatment of intraocular hemorrhage or vascular disease is not as good as argon ion laser. Argon ion and krypton ion lasers are two similar gas lasers. The former can generate continuous blue light with a wavelength of 488.0 nm and a green light with a wavelength of 514.5 nm, while the latter can generate green light with a wavelength of 520.8 nm and a red light with a wavelength of 568.2 nm. Since these five spectral lines can be strongly absorbed by pigment tissue without damaging the refractive medium transparent to visible light, it can be applied to all indications of ruby laser. In particular, the four spectral lines of blue and green light of argon ion laser and green and yellow light of krypton ion laser can be strongly absorbed by oxidized hemoglobin, so it can also be used to treat intraocular blood vessels and hemorrhagic diseases. Because the yellow and red light of the krypton ion laser is not absorbed by lutein, the damage to the upper layer of the retinal nerve is small, so it is better to treat macular degeneration. The red light can also act on the pigment epithelium through the hemorrhage of the superficial retina, which cannot be replaced by other wavelengths of laser light. The main feature of the dye laser is that its output wavelength is continuously adjustable, and it can be output continuously or in pulses. At present, the Rhodamine 6G pulsed dye laser, with wavelengths of 585.0 nm and 555.0 nm, is currently used in clinical practice. Because the wavelength of dye lasers is difficult to be continuously tunable in practical applications, and the output is not very stable, the characteristics of continuously tunable lasers have not really been exerted at present, and there are not many clinical applications. The wavelength of Nd:YAG laser is 1064nm, which is an invisible infrared light, which is not absorbed by the pigmented tissue in the eye, so it is used to treat the lesions of the non-pigmented tissue of the anterior segment. The Nd:YAG laser in the Q-switched mode can concentrate a considerable amount of energy in a very short period of time, and use the effects of photochemical, photoelectric field, and light discharge pressure to complete the penetration of transparent tissue. Because of its extremely short duration, it does not cause thermal damage, and is mainly used for cataract capsulotomy, peripheral iridotomy, and vitrectomy. There is also a frequency-doubling Nd:YAG laser that changes the output wavelength to 532nm through crystal conversion. Since it is green light, the application X range is the same as the aforementioned green light. Because it is a solid-state laser, the stability is better than that of a gas laser, and it is small in size and light in weight. Among the excimer lasers used in ophthalmology clinics is the argon fluoride (ArF) laser, which outputs far-ultraviolet light with a wavelength of 193 nm. Acts as a “cold knife” to break biomolecular bonds. Using this kind of knife to perform light resection, its cutting accuracy can reach μm level, the X circumference of the incision edge is only nm level, and because there is no thermal effect, it will not damage adjacent tissues. Therefore, it has been used in corneal surgery, such as corneal flexion. Photosurgery, corneal scar removal, etc. Subepithelial excimer laser keratectomy (Lasek) [l] Method: 20% ethanol infiltrates the corneal epithelial cell marked area, and the corneal epithelial cell layer in the marked area is completely uncovered. The corneal epithelium layer resets. 〔2〕Advantages Less postoperative pain and faster recovery than PRK. [3] Problems At present, opinions are still inconsistent, and other complications of PRK may still exist due to the ablation of the anterior elastic layer.

Lasers are not only used for the treatment of eye diseases, but also play a great role in examining and diagnosing eye diseases, such as refraction tables that use lasers for optometry and multiple inspections; Corneal topograph; with confocal laser fundus examination system, it includes confocal laser fundus tomography system, confocal laser Dochener fundus flowmeter, confocal laser fundus angiography system, which is the most advanced fundus examination system at present, its functions are:

1. Confocal laser fundus tomograph is the use of confocal laser scanning microscopy for the diagnosis of eye diseases. This technology enables ophthalmologists to accurately obtain topographic maps of different areas of the patient’s fundus, which can be used to diagnose the optic nerve head in the diagnosis of euoptic eye. Analysis, macular degeneration examination, retinal detachment assessment, ocular tumor analysis and follow-up research, fundus pathological research of diabetes, especially suitable for quantitative recording and analysis of disease changes during treatment and follow-up research.
2. Confocal Laser Fundus Angiography System Using advanced confocal laser scanning technology, digital angiography images of sodium fluorescein and indo-indocyanine green (ICG) can be acquired individually or simultaneously, and are high-quality three-dimensional real-time images. Early and late image quality is excellent. Confocal laser scanning technology ensures spatial and axial measurement accuracy. It detects and draws light from the focal plane and its vicinity, while reflected or scattered light outside the focal point is blocked from detection. Therefore, this confocal technique has two outstanding advantages of obtaining three-dimensional angiographic information and high resolution of angiographic images.
3. Confocal laser Doppler fundus flowmeter It combines two complex detection methods—confocal laser scanning laser Doppler blood flow into one, and can obtain the blood flow perfusion map of the fundus retina or optic disc non-invasively . Two-dimensional scanning of the retina or optic disc using an infrared laser. The optical Dopping effect refers to the change of the frequency of the reflected light and the divergent light produced by the moving object to the illuminating light. The reflected light of these frequency changes interferes with the opposing light of the fixed object, resulting in a detectable instantaneous light intensity change.