OBJECTIVE Measurement of the intraocular pressure (IOP) is an important tool for glaucoma diagnostics in children or patients with impaired cooperation. General anesthesia (GA) may significantly influence the IOP. This study aimed to evaluate the reduction of IOP during GA. METHODS The IOP was measured in 229 patients in a recumbent position in the non-operated eye prior to and 5 min after the beginning of GA with a dynamic contour tonometer (DCT). RESULTS The average IOP decreased from 19.9 ± 3.7 mmHg prior to GA to 14.1 ± 3.5 mmHg 5 min after beginning GA (p < 0.0001, IOP decrease 30 %). The GA caused a decrease of up to 2 mmHg in 6.1 %, 2-4 mmHg in 18.8 %, 4-6 mmHg in 21.0 %, 6-8 mmHg in 36.6 %, 8-10 mmHg in 13.6 %, 10-12 mmHg in 2.2 % and more than 12 mmHg in 1.7 % of the eyes. The ocular pulse amplitude (OPA) decreased from a mean of 3.4 ± 1.5 mmHg to 1.9 ± 1.0 mmHg (p < 0.0001, OPA decrease 41 %) under GA. CONCLUSIONS A significant decrease of IOP (mean 6 mmHg) occurs during GA and under extreme conditions up to 13.8 mmHg. A decrease of OPA of 1.5 mmHg should be taken into consideration for patients under general anesthesia and under extreme conditions up to 7 mmHg.