RECAS is a prospective cohort of 1,000 patients with carotid artery stenosis (CAS) and undergoing revascularization therapy or standard medication treatment alone. The goal of this study is to validate whether CAS revascularization when compared to standard medication treatment alone, can effectively reduce the progression of Cerebral small vessel disease (CSVD) burden, as well as improve the severity of retinal pathologies and cognitive impairment. Therefore, Patients aged ≥ 40 years have more than 50% stenosis in unilateral carotid artery and sign informed consent will be recruited. In this study, patients will be asked to undergo Computed Tomography Angiography (CTA)/ Digital Subtraction Angiography (DSA), Computed Tomography Perfusion (CTP),multimodal Magnetic Resonance Imaging (MRI), Optical Coherence Tomography Angiography (OCTA) and neuropsychological testing. Estimated follow-up can be up to 10 years.