Measurements in the peripheral retina using LDF and laser interferometry are mainly influenced by the choroidal circulation

Purpose. Two laser based methods for the assessment of ocular hemodynamics in humans have been investigated: laser Doppler flowmetry (LDF) and laser interferometric measurement of fundus pulsation amplitude (FPA). When the laser with either of the two methods is focused onto the fovea it is obvious that only choroidal blood flow contributes to the signals. When the laser is, however, directed to other parts of the retina the situation is more complex. Whereas the retina shows a pronounced vasoconstrictor response to systemic hyperoxia the effect in the choroid is small. We therefore investigated the effect of 100% O₂ breathing on results as obtained with the above mentioned techniques at different fundus locations. Methods. Twelve healthy subjects were included. Four 15- minutes 100% O₂ breathing periods were scheduled for each subject. During two of these breathing periods LDF was performed at the fovea (ChBFf) and at a fundus location approximately 7.5 degrees nasally to the fovea (ChBFp), respectively. During the other two periods FPA was assessed at the same fundus locations (FPAf, FPAp). Results. ChBFf tended to decrease during 100% oxygen breathing (6 ± 4%), but this effect was not significant. The decrease in ChBFp (10 ± 4%), was comparable. FPAf (10 ± 2%; P < 0.001) and FPAp (13 ± 2%; P < 0.001) decreased significantly during systemic hyperoxia, but again there was no difference in the response obtained at the two fundus locations. Conclusion. When LDF and FPA are applied at the peripheral retina the obtained signal is mainly influenced by the choroidal circulation.