Factors associated with choroidal blood flow regulation in healthy young subjects

PURPOSE. To analyze regulation of subfoveal choroidal blood flow (FLOW) during isometric exercise in healthy subjects in dependence of intraocular pressure (IOP), mean arterial pressure (MAP), ocular perfusion pressure (OPP), age, sex, fasting glucose, cholesterol, triglycerides, creatinine, and C-reactive protein levels and hematocrit. METHODS. We retrospectively analyzed results obtained in 261 healthy subjects who underwent a period of 6 minutes of isometric exercise during which FLOW was measured continuously and MAP was measured every minute. From these data, OPP and choroidal pressure/flow curves were calculated. Subjects were grouped into tertiles with regard to the dependent variables, and pressure/flow relationships were compared. RESULTS. Choroidal blood flow started to increase at OPP values of approximately 65% dependent on the MAP/IOP tertile. A significant increase of FLOW from baseline was noted at 67.7 ± 2.1% in the lowest MAP tertile, at 67.7 ± 2.0% in the second MAP tertile, and at 61.8 ± 2.0% in the highest MAP tertile (P ¼ 0.01). At the three IOP levels, FLOW started to increase at an OPP increase of 69.8 ± 2.1%, 70.1 ± 2.2%, and 65.4 ± 1.9% above baseline, respectively (P ¼ 0.03). Choroidal pressure/flow curves were independent of the other variables. CONCLUSIONS. The present analysis indicates that FLOW regulation during isometric exercise is dependent on absolute MAP as well as IOP levels. This indicates that regulation depends on pressure levels at both the arterial and the venous side of the choroidal circulation and highlights the complexity of FLOW regulation during changes in OPP that cannot be simply characterized by classical autoregulation models.