Effect of acute intraocular pressure changes on short posterior ciliary artery haemodynamics

Background/aims-Vascular insufficiency due to abnormal autoregulation has b een proposed as a major factor in the development of glaucoma. The anterior optic nerve is primarily perfused by the short posterior ciliary arteries. The autoregulatory capacity of these vessels in response to acutely elevat ed intraocular pressure (IOP) was examined in normal human subjects. Methods-Colour Doppler imaging was performed on the short posterior ciliary arteries of 10 normal subjects at baseline and during four incremental IOP elevations. Using a scleral suction cup placed temporally, IOP was elevate d to approximately 25, 30, 40, and 50 mm Hg. Additional measurements were p erformed immediately after pressure release. Systolic and diastolic flow ve locities were measured and Pourcelot's resistivity index was calculated. Results-Systolic and diastolic flow velocities decreased linearly with each incremental increase in IOP (p<0.001). Pourcelot's resistivity index incre ased linearly with each incremental increase in IOP (p<0.001). Changes in e nd diastolic velocity, peak systolic velocity, and Pourcelot's resistivity index were Linearly related to changes in IOP. Conclusion-The normal healthy eye is not able to autoregulate to maintain P CA blood flow velocities in response to acute large elevations in IOP.