Changes in Choroidal Blood Flow and Morphology in Response to Increase in Intraocular Pressure.

Purpose The purpose of this study was to determine the effects of an elevation in IOP on the choroidal blood flow and morphology. Methods We studied 27 healthy subjects. The mean blur rate (MBR) determined by laser speckle flowgraphy was used to measure the choroidal blood flow. The subfoveal choroidal thickness (SFCT) was measured in the optical coherence tomographic images of the macular region. The luminal and stromal areas of the choroid were determined by the binarization method before, during, and after the IOP was elevated 20 and 30 mm Hg with pressure using an ophthalmodynamometer. Results The ocular perfusion pressure (OPP) was significantly reduced by the elevation of the IOP by 20 (-52.0%, P < 0.001) and 30 mm Hg (-77.9%, P < 0.001). The percentage reduction in the macular choroidal MBR was -32.5% at an IOP elevation of 20 mm Hg (P < 0.001) and -46.6% at an IOP elevation of 30 mm Hg (P < 0.001). The SFCT was reduced by -3.8% (P = 0.014) and -7.7%, (P < 0.001) during an elevation of IOP of 20 and 30 mm Hg, respectively. The luminal area of the choroid was reduced during an elevation of the IOP of 20 (P = 0.001) and 30 mm Hg (P < 0.001). However, the stromal area did not change significantly. There was no significant correlation between the reduction ratio of OPP and other factors during the elevation of 20 mm Hg, but the correlation between the reduction ratio of OPP and the choroidal MBR during the elevation of 30 mm Hg was significant. The choroidal MBR had recovered significantly at 7 (P = 0.037) and 10 minutes (P = 0.022) compared with that immediately after the IOP elevation of 30 mm Hg. Conclusions The choroid can autoregulate its blood flow in response to experimental changes in the OPP induced by IOP elevations.