Human conjunctival microvasculature assessed with a retinal function imager (RFI)

Abstract

The conjunctival and cerebral vasculatures share similar embryological origins, with similar structural and physiological characteristics. Tracking the conjunctival microvasculature may provide useful information for predicting the onset, progression and prognosis of both systemic and central nervous system (CNS) vascular diseases. The bulbar conjunctival vasculature was imaged using a retinal function imager (RFI, Optical Imaging Ltd, Rehovot, Israel). Hemoglobin in red blood cells was used as an intrinsic motion-contrast agent in the generation of detailed noninvasive capillary-perfusion maps (nCPMs) and the calculation of the blood flow velocity. Five healthy subjects were imaged under normal conditions and again under the stress condition of wearing a contact lens. The retina was also imaged in one eye of one subject for comparison. The nCPMs showed the conjunctival microvasculature in exquisite detail, which appeared as clear as the retinal nCPMs. The blood flow velocities in the temporal conjunctival microvasculature were 0.86±0.08 (mean±SD, mm/s) for the bare eye and 0.99±0.11 mm/s with contact lens wear. It is feasible to use RFI for imaging the conjunctival vasculature.

Figure 1. Human retinal and conjunctival microvascular assessed with a retinal function imager (RFI)

The bulbar conjunctiva (A) of a healthy subject was imaged, and measurements of the conjunctival capillary perfusion (B) and blood flow velocity (unit: mm/s) (C) were obtained. Similarly, the fovea of another healthy subject (D) was imaged, and measurements of the capillary perfusion (E) and blood flow velocity expressed in mean ± SD (unit: mm/s) (F) were obtained. The avascular zone was evident in the fovea. Note that negative values (red) indicate blood flow moving away from the heart and that the vessels are arteries. Positive values (pink) represent the veins.

Figure 2. Human conjunctival microvasculature underneath a contact lens

The bulbar conjunctival region (A) of the same healthy subject shown in Figure 1 was imaged with a soft contact lens in situ, and measurements of the bulbar conjunctival capillary perfusion (B) and blood flow velocity (unit: mm/s) (C) were obtained. Note, bulbar conjunctival capillary perfusion is clearly shown, (B) and the lens edge is visible (A-C). Note that negative values (red) indicate blood flow moving away from the heart and that the vessels are arteries. Positive values (pink) represent the veins.

Figure 3. The microvasculature of the human conjunctiva

A: An RFI image showing vessels on the temporal region of the conjunctiva. B: nCPM of the same region. C: Quantification of the conjunctival blood-flow velocity expressed in mean ± SD (unit: mm/s). The images show several arteries (red) and veins (pink) that were confirmed by viewing the flow movie from the same region. Note that negative values (red) indicate blood flow moving away from the heart and that the vessels are arteries. Positive values (pink) represent the veins. D: A single frame of a flow movie showing erythrocyte clusters (black) and gaps (white) moving in the small vessels marked as yellow arrow. Red arrow: artery; Pink arrow: Vein.