Laser coagulation

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The laser or photocoagulation (doctors in jargon abbreviated as "LK") is a surgical treatment method for thermal denaturation of tissue which is preferably in the ophthalmology is used, there frequently than routine procedure in certain diseases of the retina . There are also a number of other areas of application beyond ophthalmology. The process began in 1949 with sunlight coagulation by Gerhard Meyer-Schwickerath and its further development by means of xenon photocoagulation, in which "normal" but highly intense flashes of light were still used. Today the green / green-blue argon laser, as well as krypton or dye laser, are mostly used in everyday clinical practice . The frequency-doubled neodymium-YAG laser, which is also used in ophthalmology, is usually used for interventions in the middle sections of the eye ( lens , iris ).

Physical basics

The absorption of the laser beams in the retinal pigment epithelium and the choroid (choroidea) by the biological light filter melanin leads to the development of heat in this area. The result is thermal cell necrosis (cell death) due to denaturation of the affected area, which first appears as white, fluffy foci and over time as dark pigmented scarring. The retinal laser coagulation is always a treatment method that destroys the retina, but this is definitely wanted and the destroyed retinal areas are usually so small or arranged in such a way that they are not perceived by the patient.

procedure

Laser coagulation on the retina is usually carried out on an outpatient basis. After placing a contact glass on the locally anesthetized cornea , the practitioner first seeks the therapy area with the help of a low-energy target beam. The therapeutic laser pulse is then triggered separately by the practitioner and is between 50 and approx. 300 ms long for retinal applications.

Applications in ophthalmology

Retinal holes and degenerations

Retinal holes can be caused by the vitreous or severe myopia . If there is only one hole and no significant retinal detachment , the edges of the hole can be "welded" to the substrate using LK and thus prevent retinal detachment. To be on the safe side, hole precursors (thinned areas of the retina in the peripheral retina, so-called degenerative areas) are surrounded by LK and thus secured.

Diabetic macular edema

The pumping activity of the retinal pigment epithelium is stimulated by fine foci of coagulation close to the center of the retina (paracentral LK). This can reduce the swelling of a diabetic macular edema and usually prevent further loss of vision. Laser focus sizes of approx. 100 µm are used. Coagulation can only be limited to areas with a particularly large number of edema- related vessel changes (focal paracentral LN) or, in the case of diffuse macular edema, the entire macula with the exception of the fovea can be coagulated with a laser dot matrix (so-called grid LN).

In ischemic maculopathy, coagulation does not make sense, as the residual vessels that are still intact can be destroyed and the clinical picture would progress. However, if there are large areas of ischemia, an LN of these (fovea-remote) areas can be useful in order to avoid proliferative retinopathy.

Severe non-proliferative and proliferative diabetic retinopathy

In the clinical pictures of severe non-proliferative and proliferative diabetic retinopathy , it is important to switch off the retinal areas that are undersupplied with blood by laser coagulation. Therefore, larger (approx. 500 µm diameter) and more herds are used. In addition, the entire retina with the exception of the macula is coagulated (panretinal LK). The individual foci should be set in a non-overlapping manner with a distance of about one focal point in order to avoid visual field defects . In the case of severe non-proliferative retinopathy, large-scale coagulation with initially approx. 1000 foci must be carried out. If there is no improvement or even further development in the ophthalmoscopic image or in angiography, up to 4000 or, in individual cases, more foci must be added. The other eye should also be examined for need for treatment. No more than 700 to 800 foci should be lasered per session in order to avoid side effects such as serous retinal detachment or changes in intraocular pressure and deterioration in night vision.

If a patient with macular edema and proliferation has to be lasered paracentrally and panretinally, then the paracentral LN should always be performed first, since the panretinal LN alone can worsen the macular edema with a significant loss of visual acuity.

In some patients with massive proliferative diabetic retinopathy there is a risk of retinal detachment (tractive amotio retinae) due to extensive LN in the long term due to scarred shrinkage of the proliferation. Scarring of the proliferation is definitely desired by the practitioner, but the shrinkage and the associated problems are not. Even so, there is usually no alternative; in such patients, the scarred proliferation membranes may have to be surgically removed by a vitrectomy .

Wet age-related macular degeneration

The macular degeneration is a disease of the central retina when it comes to a vessel growth beneath the retina. With the LN you can specifically burn these vessels, but the retina is always damaged, which can lead to impaired vision or the appearance of black spots ( scotomas ). The immediate center of the retina, the fovea, must never be coagulated with the argon laser, as this would lead to an irreversible and massive loss of visual acuity. There are other therapeutic methods ( photodynamic therapy , injection therapies with e.g. Avastin) for the treatment of new blood vessels under this area of ​​the retina .

Retinopathy of premature infants

In premature retinopathy , too , timely laser coagulation of the peripheral parts of the retina can prevent the disease from progressing to the point of complete retinal detachment.

Alternatives

Since laser coagulation takes place through light, the lens, cornea and vitreous body in the eye must be sufficiently clear and must not be clouded. Cloudiness can be caused, for example, by a cataract (cataract) or by dense vitreous hemorrhage.

In such a case, so-called cryocoagulation is used, in which a probe at a temperature of around −70 ° C is held against the eye under local anesthesia. The conjunctiva and cornea are not damaged, but the retina, just like with laser coagulation, is obliterated (cold-induced cell necrosis) and forms scars in the desired areas. The results are almost the same as with laser coagulation, but the procedure is more complex and not as easy to dose as LK. This method is used more often in rubeotic secondary glaucoma and in very peripheral retinal holes .

Applications outside of ophthalmology

In addition to the application on the eye described here, laser coagulation is also used for various other indications, including in the areas of dermatology , prenatal medicine and urology .

See also

literature

Individual evidence

  1. ^ Entry on laser coagulation in the Flexikon , a Wiki of the DocCheck company
  2. ↑ G. Meyer-Schwickerath : light coagulation. A method of treating and preventing retinal detachment. In: Albrecht von Graefe's Archives for Ophthalmology. Volume 156, Number 1, 1954, pp. 2-34, PMID 14349833 .
  3. ↑ G. Meyer-Schwickerath: Coagulation of the retina with sunlight. in: Reports of the German Ophthalmological Society, Vol. 55 (1949), pp. 256-259
  4. ↑ G. Peeva, P. Chaveeva, E. Gil Guevara, R. Akolekar, KH Nicolaides: Endoscopic Placental Laser Coagulation in Dichorionic and Monochorionic Triplet Pregnancies. In: Fetal Diagnosis and Therapy . Volume 40, number 3, 2016, pp. 174-180, doi: 10.1159 / 000443792 , PMID 26910557 (review).
  5. ↑ J. Akkermans, SH Peeters, FJ Klumper, E. Lopriore, JM Middeldorp, D. Oepkes: Twenty-Five Years of Fetoscopic Laser Coagulation in Twin-Twin Transfusion Syndrome: A Systematic Review. In: Fetal Diagnosis and Therapy . Volume 38, number 4, 2015, pp. 241-253, doi: 10.1159 / 000437053 , PMID 26278319 (review).
  6. ^ J. Heisterkamp, ​​R. van Hillegersberg, JN Ijzermans: Interstitial laser coagulation for hepatic tumors. In: British Journal of Surgery . Volume 86, Number 3, March 1999, pp. 293-304, doi: 10.1046 / j.1365-2168.1999.01059.x , PMID 10201768 (review).
  7. ↑ JN Kabalin: Laser coagulation prostatectomy: evolution of clinical practice and treatment parameters. In: Journal of Endourology. Volume 9, number 2, April 1995, pp. 93-99, doi: 10.1089 / end. 1995.9.93 , PMID 7543332 (review).
  8. ↑ D. Jocham: Superficial bladder cancer: primary treatment with TUR with or without laser-coagulation. In: Recent results in cancer research. Advances in cancer research. Progres dans les recherches sur le cancer. Volume 126, 1993, pp. 135-142, PMID 8456184 (review).