Retinal Vessel Leakage in Cerebral Small Vessel Disease

The goal of this observational study is to learn about leakage from retinal vessels in cerebral small vessel disease. The main questions it aims to answer are: * Does retinal vessel leakage occur in cerebral small vessel disease? * If it does, is the severity of retinal vessel leakage similar to the severity of cerebral small vessel disease generally? Participants will be tested using fluorescein angiography. This involves an intravenous injection of fluorescent dye, and is a very sensitive way to find leakage from retinal blood vessels. Participants will have already had brain scans and other examinations and tests to measure the severity of their cerebral small vessel disease. Our new retinal images will complement the information from these previous tests.