: conjunctivae) is a thin mucous membrane that lines the inside of the eyelids and covers the sclera (the white of the eye).

Because of oxygen diffusion, hypoxic bulbar conjunctival vessels will rapidly reoxygenate (in under 10 seconds) when exposed to ambient air (i.e. when the eyelid is open).

Closing the eyelid stops this oxygen diffusion by placing a barrier between the bulbar conjunctival microvessels and ambient air.

[25][26][27] With such high-magnification imaging systems, it is possible to see groups of individual red blood cells flowing in vivo.

[29][30][31] The bulbar conjunctival microvasculature is known to dilate in response to several stimuli and external conditions, including allergens (e.g. pollen),[32] temperature,[33] time-of-day,[33] contact-lens wear,[13] and acute mild hypoxia.

[34] Type 2 diabetes is associated with an increase in average bulbar conjunctival vessel diameter and capillary loss.