Microcirculation is clearly visible and can be observed on the conjunctival mucosa by means of any microscope and notably with the slit lamp microscope of ophtalmologists. A glance at the conjunctival vessels may provide useful information on the quality of microcirculation generally and on the ischaemic or oedematous repercussions of lesions affecting the kidney, the brain and other organs. The vascular alterations detectable on the conjunctiva are described. The retina also may present with abnormalities of microcirculation. Their easy detection on the conjunctiva should lead to a more complete ophthalmic and systemic exploration.