[Ocular blood flow regulation in glaucoma - examination with the ocular pressure flow analyzer (OPFA)]

Abstract

Background: The results of studies of ocular blood flow (BF) regulation of patients with primary open-angle glaucoma (POAG), normal-tension glaucoma (NTG) and ocular hypertension (OH) are presented.

Methods and patients: Examinations were carried out with the "OPFA", a newly developed ocular pressure flow analyzer (producer: tpm Lüneburg) on 92 patients with newly diagnosed glaucomas, among whom 48 patients had POAG, 22 NTG and 22 OH, and compared with age-matched groups of healthy subjects. The OPFA uses pneumatic coupling through special scleral suction cups to record ocular pulses with highly sensitive transducers and a suction pump for simultaneously increasing intraocular pressure (IOP). Following local drop anaesthesia on both eyes, IOP is artificially raised to suprasystolic values. While continuously lowering IOP, the ocular pulse is then recorded with increasing ocular perfusion pressure. We obtain the relative ocular pulse blood volume by correlating the ocular pulse amplitudes with a calibration volume of 1 µl. This enables us to collect reproducible data on intra- and inter-individual pulse blood volume (PVoc). The ocular perfusion pressure pulse blood volume curve characterizes the respective individual ocular circulation as well as systolic and diastolic ocular perfusion pressures.

Results: In healthy subjects, the ocular pulse blood volume remains stable over a certain range of ocular perfusion pressure (ppoc) changes. After exceeding a critical point (CP), the ocular pulse blood volume drops. We refer to the difference between the CP and IOP as the autoregulatory capacity (AC). In patients with POAG and in patients with NTG, the AC was reduced significantly compared with the groups of healthy subjects. The mean AC of patients with OH remained within the normal range. The ROC curves showed at an optimal cut-off value for POAG a sensitivity of 75.0 % and a specificity of 97.9 %, for NTG a sensitivity of 77.3 % and a specificity of 100 %. In patients with POAG and OH, the ocular arterial pressures were elevated. In patients with NTG they remained unchanged compared with the healthy subjects. The ocular perfusion pressures did not change in POAG as well as in NTG and OH.

Conclusions: In patients with POAG and in patients with NTG the ocular BF regulation was impaired and detected by the OPFA device with a high level of reliability. Ocular arterial blood pressures were increased as a result of vascular regulation to keep up the ocular perfusion pressure and to maintain ocular perfusion.