This study aimed to investigate changes in Schlemm's canal, intraocular pressure and ocular blood circulation following the activation of the sympathetic nervous system. Twenty healthy volunteers were enrolled in this study. The cold pressor test (CPT) was adopted. Cross-sectional area of Schlemm's canal (SCAR), superficial and deep retinal vessel densities (s-RVD;d-RVD), pupil diameter (PD), intraocular pressure (IOP), mean ocular perfusion pressure (MOPP) and heart rate variability (HRV) were measured at three time-points: baseline (T0) and 5 min (T1) and 10 min (T2) after the CPT. After cold stimulation, LF/HF index (the ratio of low frenquency and high frenquency) increased significantly. IOP decreased from 16.9 +/- 1.9 mmHg at baseline to 16.4 +/- 2.7 mmHg at T1 and to 15.2 +/- 2.7 mmHg at T2. The nasal cross-sectional area of SCAR (SCAR-n) increased from 6283.9 +/- 2696.2 mu m(2) at baseline to 8392.9 +/- 3258.7 mu m(2) at T1 and to 10422.0 +/- 3643.8 mu m(2) at T2. The temporal cross-sectional area of SCAR (SCAR-t) increased from 6414.5 +/- 2218.7 mu m(2) at baseline to 8610.8 +/- 2317.1 mu m(2) at T1 and to 11544.0 +/- 4129.2 mu m(2) at T2. The expansion of Schlemm's canal was observed after the CPT might be caused by sympathetic nerve stimulation, subsequently leading to decreased IOP.