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Background The influences of intraocular pressure (IOP) elevations on the pulse waveform in the optic nerve head (ONH) were evaluated using laser speckle flowgraphy (LSFG) in normal subjects. Methods This prospective cross-sectional study was conducted at the Nagoya University Hospital. An ophthalmodynamometer was pressed on the sclera to increase the IOP by 20 mmHg or 30 mmHg for 1 min (experiment 1, 16 subjects) and by 30 mmHg for 10 min (experiment 2, 10 subjects). The mean blur rate (MBR) and the eight pulse waveform parameters determined using LSFG were measured before, immediately after and during an IOP elevation, and after the IOP returned to the baseline pressure. Results A significant elevation in the IOP and a significant reduction in the ocular perfusion pressure (OPP) were found after applying the ophthalmodynamometer (both, P < 0.001). The blowout score (BOS) reduced significantly (P < 0.001), and the flow acceleration index (FAI; P < 0.01) and resistivity index (RI; P < 0.001) increased significantly immediately after increasing the IOP by 20 or 30 mmHg (experiment 1). The BOS reduced significantly (P < 0.001), and the FAI (P < 0.01) and RI (P < 0.001) increased significantly after the IOP elevation by 30 mmHg in both experiment 2 and 1. However, the BOS and RI recovered significantly at time 10 compared to that in time 0 (immediately after IOP elevation) during the 10-min IOP elevation (P < 0.001 and P = 0.008, respectively). Conclusions In conclusion, the BOS, FAI, and RI of the pulse waveforms changed significantly with an acute elevation in the IOP. The change should be related to the larger difference between the maximum and minimum MBRs during the IOP elevation.

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Background: To determine whether autoregulation of the blood flow is present in the blood flow on the optic nerve head (ONH) by intraocular pressure (IOP) elevations using pulse waveform parameters determined by laser speckle flowgraphy (LSFG) in normal subjects.Methods: We conducted this prospective cross sectional study at the Nagoya University Hospital. An ophthalmodynamometer was pressed on the sclera to increase the IOP by 20 mmHg or 30 mmHg for 1 min (Experiment 1, 16 subjects) and by 30 mmHg for 10 min (Experiment 2, 10 subjects). The mean blur rate (MBR) and the eight pulse waveform parameters determined by LSFG were measured before, immediately after and during an IOP elevation, and after the IOP returned to the baseline pressure.Results: A significant elevation of the IOP and a significant reduction in the ocular perfusion pressure (OPP) were found after applying the ophthalmodynamometer (both, P<0.001). The blowout score (BOS) (P<0.001) was significantly reduced, and the flow acceleration index (FAI; P<0.01) and resistivity index (RI; P<0.001) was significantly increased immediately after increasing the IOP by 20 or 30 mmHg (Experiment 1). During the IOP elevation throughout the 10 min, the BOS and the RI significantly recovered to the baseline at time 10 compared to time 0, (P <0.001 and P = 0.008, respectively) (Experiment 2).Conclusions: Our results indicate that the blood flow on the ONH is autoregulated by several mechanisms for changes in the OPP induced by an elevation of the IOP in normal subjects.