By pressure made on the eyeball with the finger placed over the junction of the eyelids at the external canthus, the intra-ocular tension can be materially increased. The tendency of this pressure is to empty the veins of the retina, to inhibit the inflow of blood into the retinal arteries, and to produce the venous pulse.
If, while this pressure is made, one watches the retinal circulation of a young child, the pulsation of the veins on the disk will be first observed; then the arteries will be seen to diminish in size and the veins to be almost emptied of blood. This is because the vessel walls are soft and resilient. In old age the walls of the vessels offer more resistance and scarcely any visible effect from the pressure is observable. In some very elderly people, however, the venous pulse is seen and a decided blanching of the
BLACK M. AN INDEX TO THE GENERAL BLOODPRESSURE: THE VENOUS PULSE AND BLANCHING OF THE RETINAL VESSELS INDUCED BY PRESSURE ON THE EYEBALL. JAMA. 1911;LVII(5):362–363. doi:10.1001/jama.1911.04260070366003
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