Background:Although the pathogenesis of glaucoma is not fully understood ,an elevated intraocular pressure (IOP) is a major factor contributing to its development and progression. The aim of this study was to investigate the changes in the retinal blood flows of the macula and optic nerve head (ONH) after an acute elevation in the intraocular pressure (IOP) observed using optical coherence tomography angiography (OCTA). Methods: This was a prospective comparative study of subjects with narrow anterior chamber angles who underwent laser peripheral iridotomies (LPIs). The IOP was measured before and one hour after the LPI. The retinal blood flows of the macula and ONH were measured using OCTA at the baseline and one hour after the LPI. Results: A total of 64 eyes of 51 individuals were enrolled in this study, and 58 eyes of 43 individuals finally completed the study with a mean IOP rise of 10.5 ± 7.6 mmHg after the LPI. Based on the magnitude of the rise in the IOP, we divided the subjects into three groups: group A = IOP rise ≤ 10 mmHg, group B = 10 mmHg < IOP rise ≤ 20 mmHg, and group C = IOP rise > 20 mmHg. The vessel density did not differ after the acute IOP elevation in either the macular region or papillary region in group A or group B (p > 0.05), but there was a significant difference in group C (p < 0.05). However, when the subjects were not separated into groups, the vessel densities of the ONH and macular region did not differ between the measurements obtained at the baseline and one hour after the LPI (p>0.05). Conclusion: In these normal subjects, an acute mild or moderate IOP elevation for one hour after the LPI did not affect the blood flow in the macula or ONH, as examined using OCTA. However, when the IOP rise was greater than 20 mmHg, the macular and papillary blood flows decreased significantly.