A new invasive method of measuring pulsatile ocular blood flow

Abstract

Abstract Purpose The purpose of this study is to demonstrate proof of principle of a new rigidity based invasive technique to assess pulsatile ocular blood flow in a wide range of clinically relevant IOP levels. Methods An invasive manometric dynamic measurement procedure is employed, using a computer controlled device, comprising a pressure transducer and a microdosimetric pump. The anterior chamber is cannulated under topical anaesthesia with drops with a 21 gauge needle and the initial IOP is recorded. The IOP is artificially set to 10 mmHg and the eye is infused with predetermined volumes of BSS in a stepping sequence. After each infusion step, the IOP is continuously recorded for 2 sec, in order to calculate the pulsatile change in IOP. Ocular rigidity is measured from the pressure volume relationship in the stepping sequence. Pulsatile Ocular Blood Flow (POBF) is obtained through algorithms converting the IOP readings to the corresponding change of ocular volume derived from the rigidity diagram. Forty eyes of 40 cataract patients were measured with this technique. The study was approved by the Institutional Board and performed under the patient’s informed consent. Systemic blood pressure and pulse rate were monitored during the measurement. Results There were no complications related to the procedure. The average Friedenwald’s Rigidity Coefficient was 0.0206 mmHg/μL (SD=0.0054). The corresponding POBF was 888(SD=185) μL/min at 15mmHg decreasing to 548(SD=146) μL/min at 40mmHg. Conclusion The invasive method described is safe and effective. It can provide accurate estimates of POBF by incorporating the individual eye’s measured rigidity coefficient. Moreover, POBF can be estimated in relation to the IOP.