A clinical study of hydrodynamic parameters of the eye in primary open-angle glaucoma and low-tension glaucoma

   PURPOSE. To quantify the outflow of intraocular fluid along various pathways depending on the stage of the disease in typical primary open-angle glaucoma (POAG) and low-tension glaucoma (LTG) cases, and compare the obtained results.   METHODS.  This study involved 30 patients (57 eyes) with POAG at various stages, aged 58 to 80 years old (mean age 67 ± 8.0 years). The comparison group included 33 patients (62 eyes) with LTG at various stages aged 51 to 80 years old (mean age 69 ± 10.4 years). All subjects had no history of previous laser or surgical interventions on the studied eye. The controls were 15 clinically healthy individuals (30 eyes) of the same age group. On the first day, electronic tonography was performed using tonograph TNC- 100-S with a 4-minute recording of the curve. On the next day, tonography was per-formed with simultaneous blockade of the  drainage outflow pathway using a perilimbal vacuum — compression ring according to the method by Prof. N.V. Kosykh.   RESULTS. The overall ease of outflow coefficient (EOC) in POAG has a pronounced tendency to decrease with stage advancement. Its decrease in the II and III stages of the disease is 35 % and 30 %, respectively. The EOC for the uveoscleral pathway with POAG decreases in the II and III stages of the disease and amounts to 33.3 % and 25 %, respectively. The ratio of uveoscleral outflow in POAG increases by 3.3 % and 6.5 % in the II and III stages, respectively. With stage I and II LTG, this indicator is stable and remains at a fairly high level, and in the III stage it decreases by 33.3 % compared to stage II. The ratio of uveoscleral out-flow in LTG increases by 21 % in the II stage and by 11 % in the III stage of the disease.   CONCLUSION. The rate of fluid outflow along the uveoscleral pathway is higher in LTG than in POAG. The ratio of uveoscleral outflow to overall outflow is greater in LTG in comparison with POAG. In this respect, it can be concluded that preservation of IOP within the limits of the average norm in LTG may be associated with a more pronounced function of the uveoscleral outflow pathway.