**4. Central retinal artery occlusion (CRAO)**

CRAO is the result of an abrupt diminuation of blood flow in CRA, severe enough to cause ischemia of the inner retina. Due to the fact that there are no functional anastomoses between choroidal (PCAs) and retinal circulation (CRA), CRAO determines severe and permanent loss of vision. Therefore, it is very important to identify the cause of CRAO, in order to protect the contralateral eye. Frequently, the site of the blockage is within the optic nerve substance and for this reason, it is generally not visible on the ophthalmoscopy. The majority of CRAO are caused by thrombus formation due to systemic diseases, including GCA. For this reason, all patients with CRAO should undergo a systemic evaluation [42–44].

#### **4.1 Spectral Doppler analysis of the orbital (retro-bulbar) vessels in CRAO**

The patients with an unilateral CRAO present at the Spectral Doppler analysis of the retrobulbar vessels the following aspects [9, 15, 16]:

a.an elevated RI in the CRAs (the RI is higher on the affected side, than it is on the unaffected side); with severe diminished blood flow velocities (especially EDV) in the CRA.

b.fewer abnormalities are observed in the PCAs, and in the OAs (**Figure 10**).

#### **Figure 10.**

*CDI of orbital vessels revealed severely diminished EDV and high RI in both CRAs (a, b) despite the fact that the left eye had the normal aspect at ophthalmoscopy. Fewer abnormalities were observed in the PCAs (c, d) [15].*
