Nocturnal intraocular pressures in patients with normal-tension glaucoma and sleep apnea syndrome

Background: About half of all normal-tension glaucoma patients and about on e third of all primary open-angle glaucoma patients have sleep apnea syndro me. If sleep apnea syndrome causes some cases of glaucoma, the optic nerve damage could result from repetitive nocturnal hypoxias or from repetitive i ntraocular pressure elevations at the end of the apneas. In this study, we determined the intraocular pressure at the end of long apneas. Patients and methods: In three patients having sleep apnea syndrome and nor mal-tension glaucoma we recorded in a sleep laboratory during at least six hours of sleep the respiration (oxymetry, nasal and oral air flow, and indu ctive plethysmography). The intraocular pressure was measured with a pneuma tonometer at predetermined times and compared to the values measured at the end of prolonged apneas. Results: The intraocular pressure during normal respiration was in the firs t patient 19.5 +/- 1.0 mm Hg OD and 19.3 +/- 1.7 mm Hg OS, in the second pa tient 25.0 +/- 4.2 respectively 25.5 +/- 4.9 mm Hg and in the third one 22 +/- 1.0 respectively 21.3 +/- 1.3 mm Hg. At the end of prolonged apneas the intraocular pressure was in the first patient 19.0 +/- 0.0 mm Hg OD and 19 .5 +/- 0.7 mm Hg OS, in the second patient 26.5 +/- 0.6 and 26.8 +/- 0.1 mm Hg and in the third one 20.0 +/- 0.0 respectively 21.0 +/- 0.0 mm Hg. The difference between intraocular pressures during normal respiration and at t he end of prolonged apneas was not significant (p > 0.1 for each comparison , paired t-test). Conclusions: We did not find an increase of intraocular pressure at the end of prolonged apneas compared to periods of normal respiration in patients with sleep apnea syndrome and normal-tension glaucoma. If sleep apnea syndr ome causes some cases of glaucoma, it seems more probable that the the opti c nerve is damaged by the repetitive hypoxias. Alternatively, an unknown fa ctor might induce both, sleep apnea syndrome and normal-tension glaucoma.