The eye is usually divided into two main sections, the anterior segment and the posterior segment. The internal structures of the anterior segment of the eye are bathed with a fluid called aqueous. Illustration of the human eye Behind the lens of the eye is the posterior segment of the eye. The posterior segment is filled with a highly viscous substance called vitreous. The vitreous pushes against the retina of the eye.
Capillaries are small vessels where arteries and veins meet.
In a healthy eye, fluids are well contained in the vessels of the retina. In some disease conditions, fluids, lipids, and other molecules leak from the vessels in the retina. These leaking areas can be identified by a special procedure called fluorescein angiography, where a fluorescein dye is injected into a vein in a person's arm, and the flow of the dye can be traced in the retina of the eye. In a healthy eye, the fluorescein does not leak out of the vessels. In disease cases, such as retinal angiomas, dye can leak into the retina.