Colour Doppler ultrasonography of the ophthalmic artery: flow parameters in normal subjects - The significance of the resistance index

Background. The aim of this study was to assess the flow characteristics in ophthalmic arteries and to detect their possible relationships to those in the common and internal carotid arteries. Methods. Sixty healthy subjects (age range 20-74 years) with normal vascula r findings, stratified by age and sex were recruited to the study. A colour Doppler ultrasound examination of the neck arteries was performed, followe d by a colour Doppler ultrasound examination of the 120 ophthalmic arteries included. Peak systolic velocity, end diastolic velocity and resistance in dex (RI) of the common carotid, internal carotid and ophthalmic arteries, a s well as the insonation depth of the ophthalmic arteries were measured. Results. The mean values (standard deviation) of the measured parameters fo r the ophthalmic arteries were: insonation depth: 38.38 mm (2.60 mm), peak systolic velocity: 34.71 cm/sec (6.38 cm/sec), end diastolic velocity: 7.95 cm/sec (1.70 cm/sec), resistive index: 0.77 (0.04). The resistance index o f the ophthalmic arteries was, in all cases, greater than that of the ipsil ateral common carotid artery which in turn, was greater than that of the in ternal carotid. The value of the index in the ophthalmic arteries, when the circulation is normal in the extra- and intracranial arteries is rarely lo wer than 0.70. Conclusions. When an inversion of the ratio between the resistance index of the ophthalmic artery and that of the common carotid or an index value low er than 0.70 in the ophthalmic artery is observed, further investigation is needed as this situation cannot be considered normal. The resistance index seems to be the most reliable parameter for the estimation of normal circu lation in ophthalmic arteries.