The Value of Doppler Study of Central Retinal Artery in Diagnosis of Increased ICP

In neurocritical care, the detection of raised intracranial pressure (ICP) remains crucial as it is associated with poor outcome . Invasive ventricular devices are the gold standard for continuous and reliable measurement of ICP however their placement could be challenging due to blood coagulation disorder or lack of surgical availability. Moreover, malfunction or obstruction of ventricular catheters has been reported to occur as often as 6%. Recently Julie.et al. revealed in his met analysis that optic nerve sheath diameter (ONSD) has a good level of diagnostic accuracy for detecting intracranial hypertension with a pooled sensitivity of 0.9. The central retinal artery (CRA) is an end artery branch of the internal carotid artery that joins the optic nerve 1cm behind the globe and enters the retina on the optic nerve head . Central retinal artery is located inside the optic nerve sheath, and The optic nerve is part of the central nervous system and the intraorbital subarachnoid space surrounding the optic nerve is subject to the same pressure changes as the intracranial compartment,so we should expect any increase of ICP will compress the central retinal artery exactly the same as basal cerebral arteries. Central retinal artery circulation is low resistance circulation with good diastolic flow and upper limit of resistivity index is 0.7. So, any compression of CRA will decrease the diastolic flow and increase RI. Kamil.et al. studied the blood flow velocity changes in orbital arteries by using Doppler sonography in eight patients with brain death and increased ICP. Peak systolic and end-diastolic velocities and resistive indices of the ophthalmic and central retinal arteries were evaluated. they observed the absence or reversal of end diastolic blood flow in these arteries. If the intracranial pressure is higher than the end-diastolic pressure of the cerebral arteries diastolic flow reversal occurs. If the intracranial pressure exceeds systolic pressure blood flow is entirely ceased with complete and irreversible loss of brain function CRA is a superficial, easy accessible without bony obstacle like transcranial doppler (TCD) and the learning curve of its Doppler study can be very steep, so it could has a big role in management of cases with increased ICP.