n. measurement of the blood pressure in the vessels of the retina of the eye. A small instrument is pressed against the eye until the vessels are seen (through an *ophthalmoscope) to collapse. The pressure recorded by the instrument reflects the pressure within the vessels of the retina. In certain disorders of the blood circulation to the eye, the pressure in the vessels is reduced and the vessels can be made to collapse by a lower than normal pressure on the eyeball.
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