What is true about Ophthalmodynamometry?

Ophthalmodynamometry is used to estimate the pressure in the ophthalmic aery (OA) at the site of origin of the central retinal aery (CRA). Measurements are performed by increasing IOP by gradually applying pressure to the globe and observing the aeries on the optic disc until they begin to pulsate. The pressure required to produce aery pulsations on the optic disc reflects the OA diastolic pressure, whereas the force required to cause cessation of aerial pulsations reflects the OA systolic pressure. In OIS(occular ischemic syndrome), the CRA perfusion pressure is low and for this reason the pressure necessary for the pulsations to appear is reduced. Diastolic readings are decreased in OIS, and may improve or return to normal after carotid aery surgery. They are considered to be more reliable than systolic readings.