Quantitative assessment of conjunctival microvascular circulation of the human eye

Abstract

Accessibility to the bulbar conjunctival microvasculature provides a means to assess blood supply to the cerebral cortex and thus optimize therapeutic interventions designed to prevent or reduce the risk of cerebral vascular disease and stroke. The feasibility of a method for quantitative measurements of conjunctiva blood vessel diameter, blood velocity, and flow in the human eye is reported. The method is based on slit lamp biomicroscope digital imaging coupled with a space time image analysis technique. A sequence of conjunctiva microvasculature images was captured at a rate of 50 Hz. The images were analyzed to determine blood vessel diameter, velocity and flow. Blood vessel diameter measurements ranged between 8.7 and 24.3 microns, with a mean value of 15.5 microns. Blood flow rate ranged between 27.3 and 296.9 pl/s, with a mean value of 111.8 pl/s. The relationship between blood flow and vessel diameter was fit with a power law curve (R=0.87). The application of this technique for in vivo quantitative assessment of blood flow dynamics has potential to impact diagnosis and monitoring of various cardiovascular and blood disorders.

Figure 1

A) An image of conjunctiva blood vessels derived by averaging 40 consecutive non-registered images; B) An image of conjunctiva blood vessels derived by averaging 40 consecutive registered images.

Figure 2

A) Blood vessel diameters and blood velocities were measured in 7 blood vessels identified on the image; B) Overlay of center line on the blood vessel segment marked by arrows. The intensity profile along the white line drawn perpendicular to the blood vessel center line (insert). The full width at half-maximum of the intensity profile is a measure of blood vessel diameter.

Figure 3

A) A space time image generated for the blood vessel V2 outlined in Fig 2B. The vertical and horizontal axes represent vessel path length and frame time, respectively; B) The best fit line to each continuous band on the binarized space time image is displayed. The line slope is a measure of axial blood velocity.

Figure 4

Relationship between blood flow rate and vessel diameter (N = 12).

Figure 5

Relationship between blood flow estimated by the power law curve derived in the current study (CS) and in a previous study (PS)(Koutsiaris, et al., 2007).