PURPOSE: To highlight the effect of ascent to high altitude on intraocular pressure (IOP) in a patient with primary open-angle glaucoma, who had previously undergone trabeculectomy in 1 eye. METHODS: Case report. RESULTS: A 66-year-old mountaineer with primary open-angle glaucoma and previous right trabeculectomy performed self-tonometry using a rebound tonometer (Icare HOME) before and during an expedition in the Himalaya. In the nonoperated eye, there was a statistically significant increase in IOP as the patient ascended to 5000 m over 8 days (R=0.790, P=0.001), consistent with recent literature. IOP increased by 1.73 mm Hg with each 1000 m increase in altitude. In the trabeculectomized eye there was no significant increase in IOP (R=0.219, P=0.172). CONCLUSIONS: Filtration surgery may be protective against IOP fluctuations associated with ascent to high altitude. Self-tonometry complements standard glaucoma care by providing opportunities for IOP monitoring outside office hours and in remote locations.