Surges in the sympathetic nervous system occur at the ictus of a variety of neurological critical illnesses including intracranial hemorrhage and ischemic stroke. It is hypothesized that these exaggerated increases in sympathetic nervous activity produce maladaptations that promote secondary brain injury. One of these possible mechanisms include diffuse vasospasm that cause cerebral ischemia. Hence, methods to abrogate the sympathetic nervous system in this context are under active investigation. One possible method is the regional anesthesia technique of the stellate ganglion nerve block, which is ordinarily used for complex regional pain syndrome, but has been shown to reduce cerebral sympathetic activity and reduces vasospasm in patients with subarachnoid hemorrhage. However, its effect on the microcirculation is not clear. Hence, we propose to study patients receiving the stellate ganglion nerve block as part of their standard medical care and to image their retinal microcirculation before and after the procedure using Optical Coherence Tomography Angiography (OCTA).