The aim of the presented study is to evaluate ocular blood flow, respectively optic nerve head blood flow in patients with carotid artery stenosis before and after carotid endarterectomy or carotid artery stenting. Additionally, the investigators aim to compare optic nerve head blood flow in patients with CAS and healthy age- and sex-matched control subjects. Furthermore, the investigators intend to evaluate brain tissue oxygenation in patients with carotid artery stenosis before, during and after CEA and carotid artery stenting. Finally, the investigators will assess potential correlations between LSFG and NIRS results in patients with unilateral carotid artery stenosis.

Carotid artery stenosis is a condition that can lead to severe consequences such as ocular ischemia or stroke. As the ophthalmic artery branches off the carotid artery, ocular ischemic complications include amaurosis fugax, ocular ischemic syndrome or central retinal artery occlusion. Hence, early diagnosis of carotid artery stenosis and ocular perfusion impairment is of considerable importance to prevent ocular and systemic ischemic complications.

As the retina offers a unique window for examining the microcirculation in a non-invasive manner, several imaging techniques have already been used in recent years to assess ocular alterations associated with carotid artery stenosis. However, these examination techniques have their limitations and are therefore not suitable methods for determining ocular perfusion. On the contrary, Laser Speckle Flowgraphy (LSFG) is a non-invasive, in-vivo imaging method which quantitatively estimates blood flow in the optic nerve head, the choroid, the retina and the iris. LSFG offers a promising alternative from conventional methods, as it eliminates the need for contrast agents, has a low procedural complexity and obtains precise and reproducible measurements.

As the eye and brain share a close vascular relationship, both receiving blood supply from branches of the internal carotid artery, there is potential to establish a correlation between cerebral and ocular hemodynamics. Near-infrared spectroscopy (NIRS) is a simple and non-invasive method which enables continuous assessment of cerebral oxygenation. However, data on the course of oxygenation of the brain tissue using NIRS before, during and after carotid interventions are scarce. Additionally, there is a lack of comparative NIRS data between carotid endarterectomy (CEA) and carotid artery stenting. Furthermore, correlation studies between oxygenation of the brain tissue and ocular perfusion are largely missing.

Hence, the aim of this study is to evaluate optic nerve head blood flow in patients with carotid artery stenosis before and after CEA or carotid artery stenting. Additionally, the investigators will compare optic nerve head blood flow in patients with carotid artery stenosis to healthy sex- and age-matched control subjects. Furthermore, the investigators intend to evaluate brain tissue oxygenation in patients with carotid artery stenosis before, during and after CEA and carotid artery stenting. Finally, the investigators will assess potential correlations between LSFG and NIRS results in patients with unilateral carotid artery stenosis.

Inclusion Criteria for patients with unilateral carotid artery stenosis:

• Men and Women aged ≥ 18 years
• Signed informed consent
• Normal ophthalmic findings, unless the investigator considers an abnormality to be clinically irrelevant
• Diagnosis of unilateral carotid artery stenosis and scheduled carotid endarterectomy or carotid artery stenting

Inclusion criteria for healthy age- and sex-matched control subjects:

• Men and Women aged ≥ 18 years
• Signed informed consent
• Normal ophthalmic findings, unless the investigator considers an abnormality to be clinically irrelevant
• Normal findings in the medical history, unless the investigator considers an abnormality to be clinically irrelevant
• Non-Smokers

Exclusion criteria for patients with carotid artery stenosis and healthy age- and sex-matched control subjects:

• Blood donation in the three weeks preceding the study
• Symptoms of a clinically relevant illness in the three weeks preceding the study
• Ocular inflammation or infection within the last 3 months
• History of family history of epilepsy
• Diabetes mellitus type 1 or type 2
• Pregnant or breast-feeding women
• Women of childbearing potential (neither menopausal, nor hysterectomized, nor sterilized) not using effective contraception

A total of 45 patients will be included in the study:

• 15 subjects with unilateral carotid artery stenosis and planned CEA
• 15 subjects with unilateral carotid artery stenosis and planned carotid artery stenting
• 15 healthy age- and sex-matched control subjects