Regulation of Choroidal Blood Flow During Forced Increase in IOP and Arterial Blood Pressure

Abstract

Abstract: : Purpose: The present study aimed at investigating choroidal blood flow regulation during simultaneous changes in intraocular pressure (IOP) and systemic arterial blood pressure. IOP was increased in stepwise increments using the suction cup method. Changes in systemic arterial blood pressure were induced by isometric exercise (squatting). Methods: 13 healthy young male subjects participated in this study. Choroidal blood flow (ChBF), mean arterial blood pressure (MAP), IOP and pulse rate were assessed at baseline and during squatting for 6 minutes with stepwise increase in IOP during the last 4 minutes. Changes in IOP were applied every 1 minute. Measurements of ChBF were performed by laser Doppler flowmetry. The IOP was measured with an applanation tonometer. Ocular perfusion pressure was calculated as OPP=2/3*MAP-IOP. For ChBF and OPP percent changes from baseline were calculated and all data are presented as mean ± SD. Results: During the first 2 minutes, isometric exercise induced an increase in OPP of +37% ± 18% while ChBF remained stable (+3% ± 6%). When IOP was artificially increased during the squatting period, a decrease in ChBF was observed (-10% ± 17%, -16% ± 19%, -19% ± 20% and -32% ± 20%, where the average IOP was 32 ± 5, 41 ± 5, 50 ± 4 and 60 ± 2 mmHg, respectively). Conclusions: Our data confirms previously published observations that the choroid shows some regulatory capacity during changes in OPP. Throughout the experiment changes in ChBF were dependent on IOP values but showed only little association with MAP.

Keywords: choroid • intraocular pressure