Factors associated with retrobulbar hemodynamic measurements at variable intraocular pressure

The authors determine those clinical variables that influence color Doppler measurements at spontaneous and artificially elevated intraocular pressure (IOP).

Color Doppler peak systolic velocity (PSV), end diastolic velocity (EDV), and Pourcelot ratio (PR) were measured in the central retinal artery (CRA) and posterior ciliary artery (PCA) at spontaneous IOP and artificially elevated IOP of 30 mmHg, 40 mmHg, and after release of suction-induced pressure elevation in 33 eyes of 33 patients. Those with varied ocular and systemic backgrounds were enrolled to facilitate determination of relationships between these hemodynamic measures at elevated IOP and multiple patient characteristics including the degree of glaucomatous damage.

Intraocular pressure elevation reduced velocity and increased Pourcelot ratio in both vessels at 30 mmHg and at 40 mmHg. On release of suction-induced IOP elevation, velocity increased above the velocity measured at spontaneous IOP (hyperemic response). Blood pressure consistently correlated with velocity and with PR in both vessels at all IOP levels tested. The change in velocity with IOP challenge decreased with age, and increased with vertical cup-to-disc ratio in the CRA, and decreased with ocular beta-blocker use in the PCA.

Because blood pressure and age relate to velocity, studies comparing cohorts with respect to disease or drug effects should be matched for these variables. While it is clear that the presence of glaucoma and use of beta-blockers correlate with vascular parameters, from this study it is not possible to distinguish pathogenic factors from pathologic results of disease or drug effects.