Evoked Cortical Responses to Electrical Stimulation of the Ischemic Retina

摘要

The objective of this program has been the early detection of the disturbances in retinal blood flow, such as ischemia, that are the precursors of blackout and unconsciousness. External electrical stimulation of the peripheral retina has been used to evoke cortical responses while still allowing normal visual function. The purpose of the present work has been to test techniques that might furnish early warning of loss of brain function or blackout resulting from high positive G forces that produce circulatory stasis in the head, particularly in the brain or eye. During the present period the electrical evoked central response (EER) technique was used at the limits of its detection capabilities and compared with similar techniques using visual stimulation. Investigations on cats were carried out to determine if a decrease in peripheral blood flow could be equated with loss of responsiveness to electrical stimulation to peripheral portions of the retina from external electrodes. Loss of function in the retina due to ischemia has been successfully monitored by using electrical stimulation of the eye to evoke cortical responses. The earliest detection of loss of function due to decreased (or cessation of) blood flow in the retina yet achieved has used the average of 4-16 responses to electrical stimulation of the eye using external electrodes. Attempts to detect single responses have not yet been successful. The details of a matched delay analogue filter designed to optimize detection of a single cortical response are given. Responses to stimulation by paired electrodes at the inner and outer canthus and the brow and cheek are compared with each other and with an electrical stimulus delivered through a corneal contact lens.