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. The cardiac myocytes of adult rats revealed elongated euchromatic nuclei. However, some myocytes displayed irregular nuclei. Numerous mitochondria appeared around the nucleus and as rows between the myofibrils. Some mitochondria were large and distorted. Glycogen granules as well as sarcoplasmic reticulum were seen in the sarcoplasm. T-tubules appeared at the level of Z-lines. Well-developed intercalated discs were identified between adjacent myocytes. Collagen fibers were observed in the intercellular spaces and around blood vessels.Examination of senile rat ventricles revealed some myocytes with irregularly-outlined nuclei. Clear perinuclear regions were observed in some cells. Other cells showed myofibrils with areas of disorganized or lost microfilaments. Mitochondria appeared between the myofibrils. Some of them were large, deformed and displayed vacuoles of different electron densities. Also, the sarcoplasm showed some vacuoles surrounded by membrane whorls. Besides, some electron dense bodies variable in size and shape were seen in the sarcoplasm. Well-developed intercalated discs with their transverse and longitudinal portions appeared between myocytes. There was a marked increase in collagen fibers in the intercellular spaces and around blood vessels which had thickened wall. Fibroblasts were also observed in the intercellular spaces.It is concluded that several age-related changes occur in the cardiac muscle that may lead to development of cardiac incompetence following loading in old age.