Glaucoma is one of the main causes of irreversible blindness in the Russian Federation and it is the leading cause of visual impairments among working age population. The primary goal of glaucoma therapy is to preserve the visual function, which is mainly achieved through persistent normalization of IOP by instillation of hypotensive drugs, laser therapy and/or surgery/ In this clinical study safety and efficacy of a glaucoma surgical technique implying valve cyclodialysis ab externo with implantation of a non-absorbable collagen implant (NACI) (Xenoplast, Dubna-Biofarm, Russia) in the supraciliary space were evaluated. All patients exhibited moderate and severe primary open-angle glaucoma (POAG). The efficacy assessment criterias were intraocular pressure (IOP) dynamics, use of hypotensive medications, need for repeat surgical intervention and complications. A total of 26 patients (26 eyes) were operated upon and under observation. Twelve months after surgery, 34% IOP decrease from the baseline level was observed: from 29.5 ± 6.8 to 18.8 ± 4.3 mmHg. The amount of hypotensive medications used reduced from 2.8 ± 0.9 to 0.6 ± 0.9. Applying the criteria recommended by the World Glaucoma Association, complete success was registered in 73.1% of patients and partial success — in 26.9% patients. No surgery ended in a failure through the follow-up period. Post-operatively, one patient developed hyphema, 2 patients had some blood elements in aqueous humor and 1 patient had shallow anterior chamber (AC). The suggested surgical technique proved to be an efficient and safe way to decrease IOP and reduce the number of hypotensive medications and had a minimal number of complications associated with the surgery, therefore it can be recommended as a method of choice in patients with advanced stage POAG.