A comparison between laser interferometric measurement of fundus pulsation and pneumotonometric measurement of pulsatile ocular blood flow. 2. Effects of changes in pCO₂ and pO₂ and of isoproterenol

Purpose. We have shown in the companion paper that, under baseline conditions, there is a high degree of association between laser interferometrically measured fundus pulsation amplitude (FPA) and pneumotonometrically measured pulse amplitude (PA) and pulsatile ocular blood flow (POBF). The present study investigated the effect of high pCO₂, of high pO₂ and of isoproterenol an POBF as assessed with laser interferometry and pneumotonometry. Methods. Pneumotonometry and laser interferometry were performed in young healthy subjects during breathing of 100% O₂ (n = 10; hyperoxia) and of 5% COP + 95% air (n = 8; hypercapnia). In addition these parameters were studied during stepwise increasing doses of isoproterenol, a β-receptor agonist (n = 8). Results. Inhalation of 5% CO₂ + 95% air increased FPA (24 + 12%, p < 0.001) PA (26 ± 13%, p < 0.001) and POBF (15 ± 8%, p = 0.002). Inhalation of 100% O₂ decreased FPA (-5 + 7%, p = 0.027), but did not change PA or POBF. The effect of 100% O₂ inhalation on FPA in the optic disc was more pronounced (-11% to -20%) than in the macula. Isoproterenol caused a dose-dependent increase in FPA, PA and POBF (p < 0.001). The association between the induced changes in FPA and PA or POBF was highly significant. Conclusions. The present study shows that FPA can be taken as a valid relative measure of pulsatile choroidal blood flow. Our results in the optic disc indicate that FPA at the neuroretinal rim and at the cup is influenced by retinal and choroidal circulation.