Comprehensive assessment of retinal, choroidal and retrobulbar haemodynamics during blood gas perturbation

Background: A study was performed to evaluate the effect of isoxic hypercap nia on ocular haemodynamics using colour Doppler imaging (CDI), scanning la ser Doppler flowmetry (SLDF) and ocular blood flow (OBF) tonography. Methods: Measurements were taken for one eye of each of 14 healthy subjects (mean age 27+/-6 years) during breathing of room air and then during isoxi c hypercapnia (breathing CO, and room air). Using CDI, blood flow velocitie s and resistance indices were determined for the ophthalmic artery (OA), ce ntral retinal artery (CRA) and short posterior ciliary arteries (SPCAs). Us ing SLDF, a 10x10 pixel frame was used to measure blood flow, volume and ve locity in each quadrant of the peripapillary retina. Pulsatile ocular blood flow (POBF) was measured using the OBF tonograph. Results: Using CDI, peak systolic and end diastolic velocities increased an d resistance index decreased significantly in the SPCAs during hypercapnia. Using SLDF, blood flow, volume and velocity increased significantly during hypercapnia in the superior temporal quadrant of the peripapillary retina. No significant difference was observed between baseline and hypercapnia fo r POBE Conclusions: Isoxic hypercapnia resulted in an increase in peripapillary re tinal and SPCA blood flow parameters as determined by SLDF and CDI respecti vely. This implies the presence of autoregulatory activity in these vascula tures. These findings may be of significance in the pathogenesis of ocular disease such as glaucoma where autoregulation is thought to be compromised.