Purpose To identify a possible link between the origin of hypertonic pain syndrome (HPS) in the eyes with terminal stage of glaucoma and the difference of the urea concentrations between vitreous contents and blood serum. Methods 31 patients (31 eyes) with refractory terminal glaucomas of different origins with IOP more 35 mm Hg were studied and operated on. The principle of surgery was drainage of the vitreous space for HPS elimination. Some vitreous contents and venous blood were taken during the surgery and researched for measuring urea concentrations. The samples were centrifuged then the blood serum and the supernatant of the vitreous contents were analyzed (SPOTCHEM‐EZ SP 4430). The patients were divided into 3 groups depending on the intensity of pain syndrome: 1st with strong pain; 2nd ‐ pain was present earlier; but it was absent before the surgery; 3d ‐ pain was never registered. Results A high concentration of urea in vitreous contents was found. Only in 6.45% the urea concentration in blood serum was higher then in vitreous. In 12.9% concentrations were near equal and in 80.64% the urea concentration in vitreous contents was higher than in blood serum. Pain existed in the cases when the difference (the negative gradient) of urea concentrations exceeded 6.1 mmol/L only. Conclusion High concentration of the osmoticaly active urea in the vitreous cavity can be the reason for increase of IOP in some cases of refractory glaucomas. If the negative gradient of the urea concentrations were higher than the critical level, it would be the reason for the development of HPS.