The basic problem in studying the physiology of retinal and ophthalmic circulation in healthy and diseased eyes is obtaining accurate and reliable clinical information about these vessels with minimal discomfort and risk.Many techniques have been developed to assess the ocular blood flow, but none has satisfied all requirements. Fluorescein angiography provided a great deal of clinical information about retinal circulation. However it is still an invasive test, and it gives only qualitative and not quantitative information.CDI provides us for the first time with an easy, reliable and non – invasive way to assess the blood flow in the ocular vessels. It represents an alternative to invasive studies such as venography and arteriography.