Changes in Pulse Waveforms in Response to Intraocular Pressure Elevation Determined by Laser Speckle Flowgraphy in Healthy Subjects

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.