Blue-green laser: the lowest penetration depth, acting with the inner and outer layers of the retina, mainly absorbed by the RPE, such as argon laser.
Green laser: Tissue penetration is stronger than blue light, absorbed by hemoglobin and RPE, 57% by RPE, and 47% by the choroid.
Yellow laser: the diffusion of the retinal nerve fiber layer is very little, the penetration force is strong, the yellow laser is absorbed by the RPE layer and the choroid inner layer to occupy 50% each.
Red light and infrared lasers: the most penetrating, mainly acting in the middle and outer layers of the choroid laser. The red laser is gradually increased by the choroid with increasing wavelength.
Absorption wavelengths of the different tissues
1. The penetration of the laser wavelength from 400 to 950 n m in the eye can reach 95%. RPE and choroid were observed at wavelengths from 450 to 630 n m
Is that the absorption rate can reach 70%. As the wavelength increases, the absorption rate quickly decreases rapidly, so the argon laser (blue-green) laser and 532 laser are the most commonly used laser spectra in the eye.
2. Light absorption characteristics of hemoglobin:
At the wavelength of 400 to 600nm (blue to yellow part), hemoglobin has a high absorption rate, while the wavelength above 600nm (red and near infrared) is very absorbed by hemoglobin, so the laser above 600 n m (red) can be used for subretinal hemorrhage.
3. Absorption characteristics of lutein:
Lutein is the photoreceptor pigment of cone cells. It has a high absorption peak for the wavelength below 480nm, which is easy to cause the damage of lutein. In order to avoid damage, the cone cells with above green wavelength is safer, among which 810 laser has the least damage.
Classification of ophthalmic lasers
Ophthalmic laser is divided into three categories: gas, liquid and solid-state laser, among which the gas laser is also divided into molecules (CO2 molecules), atoms (helium-neon atoms) and ion (argon ion and krypton ion) laser. Liquid laser has a dye laser. Solid-state laser has a ruby shock
Light, Nd: YAG laser, semiconductor laser. There are two application pathways: intraocular and extraocular pathways. Intraocular laser is used as an intraocular laser during the vitreous surgery. There are two ways to use the extraocular laser, one is through the pupil, the other is transscleral.
Principles of the fundus photocoagulation therapy
The principle of photocoagulation therapy for fundus disease is that the laser is absorbed by the pigment of the fundus. Thermal energy changes the tissue in which it acts for therapeutic purposes. The fundus absorption of the laser material is mainly melanin, followed by the hemoglobin of lutein. The tissue containing melanin in the fundus is the retinal pigment epithelium and the choroid. The absorption curves of these pigments and hemoglobin at different wavelengths are the basis for laser photocoagulation. Fundus pigment absorption after laser heat energy can make tissue coagulation, necrosis and inflammation, and then computer to achieve tissue adhesion, can also directly make the retinal neovascular and microhemangioma closed, directly destroy the retinal tissue producing neovascular growth factor and tumor tissue on the retina and choroid.
Four elements of laser photocoagulation
The four elements of laser technology refer to the wavelength, spot size, exposure time and output power, which is very important and can not be ignored in the completion of fundus laser treatment technology, is very related to the treatment effect, and is the key to ensure the realization of effective retinal spot.
The principle of wavelength selection
The choice of wavelength is mainly determined by the site and nature of the lesion. When there are a variety of wavelength lasers, the most appropriate laser wavelength can be selected, but when only a single wavelength laser, the choice does not exist, which can play the function of other parameters.
Argon laser (blue-green laser): it mainly acts on the inner and outer layers of the retina. Such as sugar mesh, vein occlusion, EALES, retinal fissure and other to choose the wavelength above green, clinical use of green light.
Green light and yellow light: they mainly act on the RPE layer and the inner choroidal layer. The retinal oedema in the macular area mostly chooses the yellow wavelength to reduce the loss of pyramidal cells; or you can also choose the green light if there is no yellow light.
Orange, red, and infrared light: mainly acting in the outer layer of the choroid. Such as choroidal neovascularization choice of deeper penetrating red wavelength. Photocoagulation of retinal microaneurysms often occurs on the tumor body, and should be selected in yellow and red.
Glass surgery wavelength selection: preferred blue-green light (488~532nm); if the retinal surface has blood, choose red light wavelength.
Choose the appropriate wavelength to achieve effective light spots and reduce complications
spot size
The actual spot size is proportional to the energy size, and is proportional to the exposure time. The closer the laser head is away to the retina, the smaller the spot is. The farther the laser head is away from the retina, the larger the laser spot is. Laser spot continuously surrounded the crack hole for 2 to 3 circles.
Argon laser retinal photocoagulation spot classification
The classification standard of continuous wave argon laser excitation retinal photocoagulation spot should be firmly kept in mind, because this is fundamentally different from the pulse wave ruby laser classification of Noyori, but some people in the domestic literature have mistakenly applied the Noyori pulse wave ruby laser classification to the argon laser retinal spot. Tso divides retinal photocoagulation spots with argon laser into 4 levels according to clinical and histopathology: Grade I spot: laser spots are only light gray, 24-hour histological changes in the acute phase are mainly vacuoles and edema of retinal pigment epithelial cells, and mild edema in optic extracellular segments and choroidal capillaries. After 1-3 months, the light spot was locally replaced by the regenerated depigmented RPE cells, appearing normally in both the outer and inner cell segments. Spot is RPE expansion, the purpose of laser is to destroy the decompensated RPE cells, stimulate the surrounding normal RPE cell hyperplasia, form a new depigmented RPE cells cover the spot area, grade I spot reaction does not form scar. Grade I spot response mainly treats RPE leakage lesions, such as mesplasmic and cystoid macular edema.
Grade light spot: the laser spot is gray-white with a peripheral light gray ring. The white center is caused by nuclear necrosis of the optic cell, because of the RPE layer necrosis damage of the optic cell range, so there is a peripheral pale gray ring. The acute 24-hour histology of the laser spot changes the RPE, the optic cells and the outer nuclear layer had necrosis, the inner core layer was normal, and the choroidal capillary thrombosis in the corresponding optical spot area was formed. After 1 – 3 months, necrotic RPE cells disappear, depigmented RPE cells on the glass membrane, macroxi cells are still in the subretinal space, and Muller's cell process enter the subretinal space to form a new outer membrane, but the optic nucleus is no longer present, and there is no scar formation in the chororetina., Laser spots do not invade the inner retinal layer, so they can not block the leaky retinal blood vessels. It is not suitable for sealing the retinal fissure and lattice degeneration areas, because the adhesion between the retinal neuroepithelium and the pigment epithelium is unstructural, and after a period of time, new gaps are created.
Grade light spot: the laser reaction spot is thick white, the outer two light gray rings are histologically changed to RPE and the inner and outer nuclear layer necrosis, the white center is the core layer necrosis, and the two outer white gray rings are the necrosis of the outer nuclear layer and RPE layer respectively. The healing phase shows moderate RPE proliferation and extension into the retina; astrocytes and Muller's cells reach the subretinal space, form chorioretinal scars with proliferating RPE cells, and capillary obstruction in the inner core layer and choroidal capillary layer. Retinal grade burn spots have light, medium, and heavy three grades. In mild cases, the core layer damage is light, glial cell proliferation is light, and the chororetinal scar formed is weak; moderate glial cells and RPE proliferation form strong chororetinal scar, and severe retinal burns are heavy, so that RPE cells cannot be covered on the glass membrane to form proliferation. Grade spots are the most valuable spot response for retinal vasoproliferative lesions. Vascular obstructive ischemic proliferative retinopathy such as diabetic retinopathy, retinal vein obstruction, retinal vasculitis should reach the retinal grade photocoagulation spot, and I and grade light spot can not cure this kind of lesion, is ineffective light spot.
Grade spot: laser reaction spot is strong white center peripheral stain white ring, histologically whole-layer retinal necrosis including the inner boundary membrane, so a strong white center, and the white ring of peripheral stain is the diffuse necrosis of RPE and optic cells, and the retinal blood vessels in the nerve fiber layer and core layer are also solidified and blocked. After 1-3 months, the whole layer of retinal atrophy, the thin glial layer polar cap damage area, often the RPE without proliferation, the chorioretinal scar does not form, and the inner boundary membrane is also ruptured. Grade burning spots are suitable for the treatment of chorioretinal tumors.
exposure time
In the macular area, 0.1s was selected, and the exposure time of the macular area (middle periphery to far periphery) was often 0.2~0.3s.
Note: When the power is high, the exposure time is short, it is easy to lead to perforation.
laser power
As for the energy setting, we should always start with the minimum energy, because there are many factors affecting the laser intensity: gas, liquid or silicone oil in the glass incision, the retina, and the state of the machine may affect the laser reaction, so the spot reaction shall prevail.
When the spot size and exposure time are fixed, the power should be put in a small position, such as 50mW, and gradually the power should be increased, such as 100,200, until the white reaction range appears.
Avoid small light spots, short time, high energy
1 Whole retinal photocoagulation (PRP)
Total retinal photocoagulation: This method is also known as bombing photocoagulation, such as PDR (proliferative sugar mesh), ANR (acute retinal necrosis), CRVO (central vein obstruction) need glass cutting surgery to remove blood or proliferators, intraoperative surgery is suitable for total retinal photocoagulation. Methods: Glass cutting removes blood accumulation or proliferator, For all retinas except the macular region of the temporal superior and inferior vascular arches, Diffuse photocoagulation is performed as much as possible from 500um around the nipple, Different size of light spots were applied by different regions, The Time and Energy, Generally can first photocoagulation after the pole part, The quadrants is then performed in entially, Spot spacing is generally 1-1.5 spot size, Time from 0.05-0.1 seconds, Energy from small to large, With the degree of occurrence stage light spot, Direct photocoagulation of the input blood vessels of the neovasculature, fused, moderately intensity 500um spots, PRP general line 1600-3000 points, Do not photocondense large blood vessels and areas of preretinal bleeding, Do not photocondense within the macular center at 1PD, Do not proceed at the chororetinal pigment scar either.
2 Local and direct photocoagulation
Local direct photocoagulation: localized photocoagulation is mainly used for retinal peribiopsitis, porous retinal detachment, Coats disease, eyeball wall foreign body removal source, retinal incision and drainage, and macular hole with high myopia. According to the sensitivity of the retina of different patients to laser irradiation, the output energy and duration are constantly adjusted, and the distance and Angle between the laser probe and the retina are adjusted, so that the mild retinal response to laser irradiation is better. During operation, attention should be paid to the spot density, between rows and 1~l.5 Spot diameter.
3 Photocoagulation of macular area
For the intraoperative findings of a clinically significant macular oedema (CSME), diffuse macular oedema, focal photocoagulation, grille-like photocoagulation or modified grille photocoagulation can be used. The method is to shoot 2-3 rows of 100um outside about 500um (i. e. outside the avascular zone), 100um apart (i. e., a spot diameter). Then the whole diffuse leaky macular area was hit with a 200um spot, 200UM apart for 0.1 seconds, to generate the energy of the grade I spot.
Note: When the macular area photocoagulation should be avoided from the fovea, from the inside and outside.
Advantages of intraocular photocoagulation
Glass surgery combined with intraocular photocoagulation has the following advantages:
(1) Photocoagulation in close proximity to the retinal surface can significantly reduce the loss of laser light in the ocular refractive interstitium, so the energy required is relatively low.
(2) Complete total retinal photocoagulation needs only about 1 000 photocoagulation point, (conventional total retinal photocoagulation outside eyes need 3 or 4 times, and need the number of photocoagulation point about more than 2000, also are reported as long as accurate grasp the laser energy, laser spot size and quantity, in vitrectomy for one-time total retinal photocoagulation treatment, the effect is safe and reliable.
(3) The size of the optical coagulation spot and the laser energy can be adjusted by adjusting the distance between the optical fiber head and the retina, and the method is simple and flexible. Laser spots have uniform pigmentation and large light spots.
(4) Photocoagulation in the eyes with the removed vitreous, can reduce the postoperative intraocular reaction, especially the vitreous reaction.
(5) Photocoagulation difficulties caused by postoperative corneal edema, difficult to have large pupil dispersion, aggravated cataract, intraocular reaction or fresh bleeding can be avoided.
(6) Because the intraoperative whole retinal photocoagulation has a control effect on PDR, the vitreous bleeding can be absorbed in the near future, so that the probability of repeated bleeding is significantly reduced.
(7) Operate under direct vision, direct photocoagulation of the lesion, the lesion display is clear and accurate positioning
Disadvantages of intraocular photocoagulation
(1) Restricted photocoagulation in the peripheral retina of the crystalline eye (especially the upper peripheral fundus)
(2) Photocoagulation may be difficult when retinal proliferation thickened
(3) Compared with the extraocular laser photocoagulation, the photocoagulation spot is large and greatly damaged
(4) Laser light can cause retinal cracks
Adverse reactions of intraocular photocoagulation
(1) Fundus laser photocoagulation on blood-retinal barrier: laser photocoagulation can cause retinal pigment epithelial cell necrosis, degeneration and inflammation, making the close link between retinal pigment epithelium, and it falls off from the Bruch membrane, resulting in blood-outer retinal barrier damage, and small impact on blood-inner retinal barrier. Disruption of the blood-retinal barrier causes the context
Blood components inside the membrane leak into the retina, and produce a series of adverse reactions such as choroidal neovascular membrane formation and proliferative vitreoretinopathy during the subsequent repair process. The time to repair when photocoagulation disrupting the blood-outer retinal barrier is related to the amount of laser used and the extent of photocoagulation. It is generally thought to repair within 14 days.
When the energy of the laser is large and the exposure time is short, the Bruch membrane will be directly destroyed by the blasting action of the laser, thus damaging the integrity of the connection between the retinal pigment epithelial cells, and causing the damage of the outer barrier between the retina and blood.
(2) Choroidal neovascularization membrane formation: laser photocoagulation has a therapeutic effect on the subretinal choroidal neovascularization membrane, but it will also cause its formation. The formation of choroid neovascularization membranes is also associated with the expansion of laser spots. The choroidal neovascular membrane can denature the neuroepithelium in contact with it. If in the macular area, it can cause vision loss.
(3) Formation of proliferative vitreoretinopathy: laser closure of the retinal cracks, and the formation of the preretinal membrane was found in the macular area. Vitoretinal proliferative lesions in preterm infants with laser photocoagulation. Severe preretinal membrane and traction were found to occur in the photocoagulation zone, and severe retinal detachment occurred later on.
(4) Choroidal leakage: the destruction of the outer retinal barrier caused by laser photocoagulation and the damage caused by the choroidal blood vessels caused by the absorption of light energy by the choroidal membrane itself prompted the blood components to enter the retina, forming choroidal leakage. Photocoagulation causes the leakage of the choroid in the ciliary body to cause changes in the anterior segment, such as a narrowing of the atrial angle and a shallow anterior chamber. The extent of this leakage is related to the pigment of the species. This leakage can cause a narrowing of the anterior chamber angle in patients with a short ocular axis.
(5) Change of the vitreous body: after the laser photocoagulation of the retina in the corresponding location of the photocoagulation spot.
(6) Maclastoid oedema: laser photocoagulation can cause proliferative vitreoretinopathy, and then traction of the macular area retina, causing macular cystoid oedema.
(7) Refractive change: hyperopia (macular forward) or myopia (choroid detachment in the periphery of the crystal-iris diaphragm forward push, anterior chamber and flattening of myopia)
(8) Elevated intraocular pressure: the choroidal leakage in the ciliary body will narrow the atrial Angle
(9) Visual field defect: the abnormal ERG of the retina occurs at the laser photocoagulation site occurs, and the damage of the retina by a large area of photocoagulation can cause the visual field defect.
Some are the adverse reactions at different tissue sites, some are performed at different time stages, and the most basic photocoagulation adverse reaction is the disruption of the blood-retinal barrier.
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