Conjunctival oxygen tension is influenced by plasma and blood volume, and flow through the external carotid artery.

An investigation of the feasibility and validity of measurement of the conjunctival oxygen tension as a monitor of peripheral circulation, blood and extracellular fluid volume and cerebral circulation was carried out in 7 healthy volunteers and 5 unconscious critical care patients with proven total cerebral infarction. The healthy volunteers were subjected to changes in hydration achieved by the administration of furosemide and subsequent rehydration by administration of normal saline. Conjunctival oxygen tension was found to be a sensitive indicator of changes in the degree of hydration presumably by its ability to detect changes in peripheral circulation depending upon circulating blood and extracellular fluid volume. A drawback is that other stimuli of the sympatho-adrenergic system such as temperature and pain, interfere with measurement in the conscious volunteer. In patients with presumed total brain infarction the conjunctival PO2 cannot be used as a reliable monitor of cerebral blood flow because of varying perfusion of the palpebral conjunctiva from the external carotid artery in the occasional patient.