Blood flow through the eye is controlled by the ocular perfusion pressure and the vascular resistance to blood flow.
ocular perfusion pressure in mm Hg for a person sitting upright =
= (2 / 3 * (mean arterial pressure in mm Hg)) – (mean intraocular pressure in mm Hg)
mean arterial pressure in mm Hg =
= ((2 * (diastolic pressure in mm Hg)) + (systolic pressure in mm Hg)) / 3 =
= (diastolic pressure in mm Hg) + (1 / 3 * (pulse pressure in mm Hg))
where:
• The intraocular pressure is a good estimate of the venous pressure leaving the eye.
• Lying down will increase the perfusion pressure, corresponding to the change in height of the eyes over the heart (Alm, page 192).
If the vascular resistance is known, then blood flow through the eye then can be calculated.
blood flow through the eye =
= (ocular perfusion pressure) / (vascular resistance)
To increase blood through the eye, then either mean arterial pressure must be increased and/or vascular resistance decreased.
