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

Abstract

Background/aims: Vascular insufficiency due to abnormal autoregulation has been 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 elevated 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 elevated to approximately 25, 30, 40, and 50 mm Hg. Additional measurements were performed immediately after pressure release. Systolic and diastolic flow velocities 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 increased linearly with each incremental increase in IOP (p < 0.001). Changes in end 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 PCA blood flow velocities in response to acute large elevations in IOP.

Figure 1

(A) The colour Doppler spectrum from the temporal short posterior ciliary artery in one subject shows the characteristic baseline waveform. (B) The waveform was maintained after the scleral suction cup was applied, but the peak systolic and end diastolic flow velocities decreased while Pourcelot's resistivity index increased. This continued with IOP increased to 40 mm Hg, and (C) 45 mm Hg. Spectral tracing below baseline in some patients suggests possible reversal of flow. (D) Following release of the suction cup there was a dramatic increase in peak systolic and end diastolic flow velocities with a decrease in Pourcelot's resistivity index. The IOP also decreased below baseline values.

Figure 2

During a continuous scan with constant position of the eye and colour Doppler probe, the peak systolic and end diastolic velocities decreased immediately after an acute increase in IOP as indicated by the arrow. The shape of the waveform remained constant.

Figure 3

(Left) Average peak systolic flow velocity (SD) significantly decreased from the baseline value after placement of the scleral suction cup (p<0.001). There was a significant linear decrease with the incremental increases in IOP (p<0.001). (Right) Three measurements made immediately after release of scleral suction and within the following 10 minutes show a significant increase in peak systolic flow velocity and a decrease in IOP to below baseline.

Figure 4

(Left) Average end diastolic flow velocity (SD) significantly decreased from the baseline value after placement of the scleral suction cup (p<0.001). There was a significant linear decrease with the incremental increases in IOP (p<0.001). (Right) There was a significant increase immediately and up to 10 minutes following release of scleral suction.

Figure 5

(Left) Average Pourcelot's resistivity index (SD) significantly increased from baseline after placement of the scleral suction cup (p<0.017). There was a significant linear increase with the incremental increases in IOP (p<0.001). (Right) There was a significant decrease immediately and up to 10 minutes following release of scleral suction.