At present, there are many kinds of lasers commonly used in the treatment of fundus diseases. Different lasers have different wavelengths, different modes of action and depth of action. Therefore, there are many different classification methods.

It can be divided into four categories: gas lasers, liquid lasers, solid-state lasers and semiconductor lasers. Among them, semiconductor lasers have low cost, small size, stable performance, and are widely used in clinical practice. Currently commonly used lasers are:

1. Argon ion laser: two wavelengths of laser can be generated after being excited: argon blue-green laser; argon green laser (wavelength 514nm).
2. Krypton ion laser: It belongs to gas laser. Three wavelengths can be generated by optical tuning: krypton green laser (wavelength 530nm); krypton yellow laser (wavelength 568nm); krypton red laser (wavelength 647nm).
3. Dye laser: It belongs to liquid laser. It can excite three spectral lasers of yellow (560-580nm), yellow-orange (580-610nm) and red (610-640nm).
4. Ruby solid-state laser: wavelength 694.3nm.
5. Frequency-doubling Nd: YAG (Fd-Nd: YAG) laser: It is an infrared laser with a wavelength of 1064 nm that is excited by a semiconductor laser to stimulate the Nd: YAG lens, and then frequency-doubling the KTP lens to produce a green wavelength of 532 nm. laser.
6. 689nm semiconductor laser: red wavelength laser, strong penetrating power, currently only used for dynamic therapy.
7. 810nm semiconductor laser: It is a near-infrared laser.

1. Continuous wave laser: Continuous wave laser is widely used in the treatment of fundus diseases at present. It not only has stable output power, but also stable retinal spot reaction during retinal photocoagulation. It is an ideal laser for the treatment of fundus diseases.
2. Quasi-continuous wave laser: From the microscopic concept, it belongs to the pulse wave category, and from the macroscopic concept, it belongs to the continuous wave category, so it is called quasi-continuous wave laser. The pulse width of quasi-continuous wave laser is different, and the effect of different width is different. When the pulse width is less than 10-5 seconds, sometimes the retinal spot reaction has the properties of pulse wave laser spot, that is, retinal hemorrhage and bubbles are easily generated.
3. Pulse wave laser: The output power of pulse wave laser is unstable, and the intensity of the retinal spot response is also unstable. Common complications are the formation of bubbles in the spot, bleeding, and even massive bleeding into the vitreous. Such lasers have been rarely used in fundus treatment.

Lasers with different wavelengths have different characteristics, and the depth and biological effects on the retina and choroid are also different. In the clinical application of lasers, the wavelength laser that has good refractive interstitial penetration and can be well absorbed by the target tissue is selected first. Fundus lasers can be classified according to wavelength and are roughly divided into green, yellow, red and infrared lasers.

There are mainly argon ion lasers, which emit lasers with a wavelength of 514 nm; frequency-doubling Nd:YAG lasers, which emit lasers with a wavelength of 532 nm; and krypton green ion lasers, which emit lasers with a wavelength of 530 nm.

1. Green wavelength laser characteristics:
① Absorption characteristics: It can be absorbed by various pigmented tissues of the fundus, and the absorption rate of oxygenated hemoglobin is 85%; the absorption rate of retinal pigment epithelium (RPE) and choroidal melanin is 73%; the absorption rate of lutein is very small.
② Penetration: The penetration is weak, and it is not easy to penetrate the lens and vitreous with moderate opacity.
③ Scattering: easy to scatter, so that the light energy is easily attenuated.

2. Green wavelength laser application:
Green wavelength laser is the most commonly used laser for retinal photocoagulation treatment, and is mainly suitable for most retinal diseases that require fundus laser treatment in the transparent state of the refractive interstitium.

3. Matters needing attention: It can be partially absorbed by lutein, resulting in macular damage; when there is extensive hemorrhage in the fundus, the retinal neuroepithelium can be damaged after the hemoglobin is absorbed, and can cause proliferative changes.

Yellow wavelength lasers mainly include 568nm krypton ion lasers and 577nm semiconductor lasers.

1. Yellow wavelength laser characteristics:
① Absorption characteristics: melanin is well absorbed; easily absorbed by hemoglobin, microangioma can be closed with small energy; not absorbed by yellow pigment (including lutein), little damage to the macula, can be used for macular diseases such as neovascular membrane, macula Treatment of edema, etc.
② Penetration: Penetration is stronger than green light, can penetrate opacity refractive media (such as lens opacity), mainly acts on the RPE layer and the choriocapillary layer; laser treatment for the macula can effectively avoid side damage ; Good absorption of hemoglobin, can directly photocoagulate abnormal retinal choroidal vessels.
③ Scattering: The light scattering of yellow laser light is small, and it is not easy to damage the retinal neuroepithelial layer.

2. Yellow wavelength laser application:
① All fundus diseases that can be treated by green laser.
② It can be used for fundus laser treatment under the opacity of refractive medium.
③ It is especially suitable for laser treatment of macular degeneration, such as macular edema, microaneurysm, choroidal neovascularization, etc.
④ Abnormal retinal choroidal blood vessels and vascular diseases. Precautions: Absorption by intravitreal hemoglobin (hemoglobin), or absorption by superficial retinal hemorrhage, can produce proliferative lesions.

Red wavelength lasers are mainly include krypton ion lasers with a wavelength of 647 nm, ruby lasers with a wavelength of 694 nm and semiconductor lasers with a wavelength of 689 nm.

1. Red laser features:
① Absorption characteristics: more absorbed by melanin, but the absorption rate of melanin to red laser is lower than that of yellow and green laser; less absorbed by lutein (7%), it can be used to treat subretinal lesions in the macula, such as the macula Extrafoveal choroidal neovascularization; it is rarely absorbed by oxygenated hemoglobin, and red wavelength laser can be used for retinal photocoagulation treatment when there is mild vitreous hemorrhage and retinal hemorrhage. It is not used to treat vascular diseases such as hemangiomas.
② Penetration: It has strong penetrating power and can effectively penetrate the lens and vitreous with mild opacity. It can be appropriately applied to retinal photocoagulation when the refractive interstitial opacity is present, but it is not the first choice for retinal photocoagulation. Its action site can reach the middle layer of choroid, which increases the secondary damage of retinal photocoagulation and the pain of patients during treatment. It is mostly used for retinal outer layer and choroid diseases.
③ Scattering: less scattering in the eye and less damage to nerve fibers.

2. Red wavelength laser application:
① Laser treatment of retinopathy in the state of refractive interstitial opacity.
② Laser treatment of subretinal lesions.
③ Precautions: The action site is deep, which can easily lead to choroidal atrophy and hyperpigmentation.

Infrared light semiconductor laser with wavelength of 810nm.

1. Characteristics of infrared wavelength laser:
① Absorption characteristics: only absorbed by melanin.
② Penetration: The penetration is stronger and can reach the middle layer of the choroid.
③ Scattering: less light scattering in the eye.

2. Infrared wavelength laser application: mainly used for transpupillary hyperthermia treatment of choroidal diseases. Matters needing attention: The laser response is slow, the spot is large and deep, the side damage is severe and the pain is strong when used for retinal laser treatment. It is not recommended for panretinal photocoagulation treatment.