The influence of posture change on ocular blood flow in normal subjects, measured by laser speckle flowgraphy

Purpose: To investigate, using laser speckle flowgraphy (LSFG), the autoregulation of ocular blood flow (BF) in response to posture change. Methods: This study comprised 20 healthy volunteers (mean age 30.0±8.5). The mean blur rate (MBR) of the ocular circulation in the subjects was assessed in both a sitting and a supine position every 2min over the course of 10min. Baseline measurements of the MBR at the optic nerve head (ONH) and the choroid were taken in a sitting position. Increases in the MBR ratio in a supine position were calculated with reference to this baseline. Intraocular pressure (IOP), systemic blood pressure and heart rate in the brachial artery were also recorded. Results: In the ONH, the MBR ratio increased significantly over the baseline after 2min (104.8±5.0%, p=0.001) and 4min (104.4±5.6%, p=0.005), in a supine position, but decreased to the initial level after only 6min. In the choroid, on the other hand, while the MBR ratio also increased significantly after 2min in a supine position (113.7±8.1%, p<0.001), it kept this significant increase over the time course of 10min. After 10min in a supine position, IOP increased significantly (p<0.001), systolic blood pressure decreased significantly (p<0.001), but diastolic blood pressure did not change significantly compared to the baseline. (p=0.07) Conclusions: ONH and choroidal circulation have significantly different hemodynamics in response to posture change in healthy volunteers. This finding suggests that LSFG enables us to assess the autoregulation of BF in the ONH.