Eye examination-induced syncope Role of trigeminal afferents

The role of trigeminal afferents in a patient with eye examination - induced syncope was investigated. A head-up tilt test precipitated presyncope with a reduced blood pressure. On a separate day, the application of Schirmer's lacrimation test strips in each conjunctival sac caused vasodepression and cardioinhibition. Topical administration of 0.5 % proparacaine hydrochloride produced ocular anesthesia and loss of corneal reflexes. Schirmer's test following anesthesia again caused presyncope with reductions in blood pressure and heart rate. The supramaximal stimulus to a supraorbital nerve before and after topical anesthesia did not affect blood pressure or heart rate. It is concluded that trigeminal afferents did not induce vasodepressive syncope in this patient. Instead, corticohypothalamic centers may have played an important role.