Feasibility of conjunctival hemodynamic measurements in rabbits: reproducibility, validity, and response to acute hypotension.

OBJECTIVE: To evaluate the feasibility of conjunctival hemodynamic measurements based on assessment of reproducibility, validity, and response to acute hypotension.
METHODS: Image sequences of the conjunctival microvasculature of rabbits were captured using a slit lamp biomicroscope under a steady-state condition, after topical administration of phenylephrine, and after intravenous administration of esmolol. Venous hemodynamic parameters (diameter, blood velocity, blood flow, and wall shear stress) were derived.
RESULTS: Conjunctival venous diameters ranged from 9 to 34 μm and blood velocities ranged from 0.08 to 0.95 mm/s. Coefficients of variation of venous diameter and blood velocity measurements were, on average, 6% and 14%, respectively. Automated and manual measurements of venous diameter and velocity were highly correlated (R = 0.97; p < 0.001; n = 16). With phenylephrine administration, diameter and velocity were reduced by 21% and 69%, respectively. Following esmolol administration, blood pressure was reduced with a concomitant decrease in velocity, followed by recovery to baseline. Venous blood velocity, flow, and WSS were correlated with blood pressure (R ≥ 0.52; p ≤ 0.01).
CONCLUSIONS: The feasibility of quantifying alterations in microvascular hemodynamics in the bulbar conjunctiva was established. The method is of potential value in evaluating microcirculatory hemodynamics related to cardiovascular function.