Argon laser trabeculoplasty

Indications for laser trabeculoplasty

It is proved that laser trabeculoplasty effectively reduces intraocular pressure in uncontrolled open-angle glaucoma, both primary and secondary. Such treatment is better suited for primary open-angle glaucoma, glaucoma with normal intraocular pressure, pigmentary glaucoma and pseudoexfoliation glaucoma. With juvenile glaucoma and secondary glaucoma, for example, neovascular and inflammatory, the results of laser trabeculoplasty are generally worse. The necessary conditions are transparency of the eyes and good visibility of the trabecular network. The opacity of the cornea and the developed peripheral anterior sinuschi can interfere with the operation of the laser. To conduct laser trabeculoplasty, one must possess the technique of gonioscopy and clearly recognize the structures of the anterior chamber angle.

Method of laser trabeculoplasty

Since the introduction into practice in 1979 of Witter and Wise of argon laser trabeculoplasty (ALT), its methodology has undergone only minor changes. To the trabecular network, 50 μm points with an energy of up to 1000 mV are applied, sufficient to cause a minimal discoloration of the pigment. To destroy the tissue, the minimum amount of energy is used.

Laser coagulants should be applied at the border of the pigmented and unpigmented part of the trabecular network. Can be carried out as one operation with the application of about 100 points along the entire circumference of 360 °, and two operations, when in semicircles of 180 °, 50 points are applied. In the course of this operation, Goldman's single- or three-mirror goniolins or Rich's goniolins are used.

To minimize the probability of occurrence of transient peaks of intraocular pressure, local a-adrenoagonists (apraclonidine and brimonidine) are prescribed before and after surgery. To prevent inflammation after laser treatment, topical glucocorticoid is used 4 times a day for a week.

1 hour after the operation, the patient is measured by intraocular pressure. When the peak of intraocular pressure occurs, inhibitors of carbonic anhydrase or hyperosmotic drugs are administered orally. The patient is re-examined after 1 week and 1 month after the intervention. During the final examination, a conclusion is made about the effectiveness of laser therapy.

Mechanism of action of laser trabeculoplasty

The developed theories of reducing intraocular pressure when using laser therapy are not confirmed. Probably, the degree of pigmentation of the trabecular network is crucial in the successful outcome of laser trabeculoplasty. Expressed pigmentation is a good precursor of a successful operation. Histologically, it has been shown that thermal action by an argon laser causes melting and deformation of trabecular beams. According to the first theory, these contract burns in the angle region mechanically contribute to a wider opening of the trabecular beams, thus facilitating the outflow of moisture. According to the second theory, laser irradiation stimulates the division of endothelial cells of the trabecular network. Since these cells perform the role of phagocytes in the angle region, it was believed that endotheliocytes purify intratrabecular spaces from detritus, which may be a cause of disturbed outflow of intraocular fluid in glaucoma.

Effectiveness of laser trabeculoplasty

After argon laser trabeculoplasty intraocular pressure, as a rule, decreases by 20-30% of the initial level. Not all patients have a reaction to laser trabeculoplasty. Positive prognostic factors of a satisfactory response: pronounced pigmentation of the trabecular network, age (older patients) and diagnosis (pigmentary glaucoma, primary open-angle glaucoma and exfoliative syndrome).

Over time, the effect of argon laser trabeculoplasty is damped. In long-term studies (5-10 years), the absence of the effect of argon laser trabeculoplasty was observed in 65-90% of cases. Repeated operation after complete circular argon laser trabeculoplasty gives at best a short-term effect with 80%

Fading within a year. Due to structural damage to the outflow system with argon laser trabeculoplasty, repeated treatment can lead to paradoxical persistent elevation of intraocular pressure. When the argon laser was repeated, the angle of the anterior chamber in animals was used by Gaasterland to create an experimental model of open-angle glaucoma. If there is a need for rapid or significant (ie, more than 30% of the pre-treatment pressure level) for reducing intraocular pressure, argon laser trabeculoplasty is not a method of choice. To achieve these goals, it is better to use drug therapy or a filtration operation.

Currently, the US algorithm for the treatment of glaucoma: drug treatment in the beginning, then argon laser trabeculoplasty and, finally, filtering operation. Such an algorithm is only recommendatory in nature, the treatment should be individual for each patient in order to ensure an optimal result. There are studies that re-examined the effects of certain treatments for open-angle glaucoma. During the GLT study, argon laser trabeculoplasty and drug therapy were compared as an initial step in the treatment of a newly diagnosed primary open-angle glaucoma. After 2 years, 44% of patients who underwent only argon laser trabeculoplasty underwent a control compared with only 20% of patients treated with timolol. In a subsequent study with an average follow-up of 7 years, 20% of patients undergoing argon laser trabeculoplasty and 15% of patients taking timolol underwent control. Despite the fact that in the design of this study there were methodological shortcomings, it confirmed that, at least for certain patients, argon laser trabeculoplasty can be the initial stage of therapy.

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