The retina has two blood supplies. The first is under the retinal called the choroid. The second is a large artery (central retinal artery) and a large vein (central retinal vein) in the center of the optic nerve. The artery has high blood pressure and a thick muscular wall, while the vein has low blood pressure and a thin wall. The retinal vessels branch multiple times, and the arteries and vein cross each other multiple times. Where the arteries cross the veins, the artery can squeeze the vein, like a garden hose, causing a clot to form. This clot blocks the vein causing blood and fluid to build up behind the clot. This results in swelling in the center of the retina (macular edema), poor blood flow impairing the delivery of oxygen and nutrients to the retina, and sometimes new abnormal blood vessel growth. Patients may lose vision due to macular edema, blood filling the eye (vitreous hemorrhages), high eye pressure (glaucoma), or tractional retinal detachments. Injections, laser, and vitrectomy surgery are used to improve vision and prevent further vision loss.
Sometimes clots can form in the artery that block blood flow to the retina. This is similar to a stroke, and will result in an area of the retina that is blind. If the center of the retina, or fovea, is involved, the central vision will drop dramatically. Unfortunately, there is no good treatment for retinal artery occlusion. However, if is very important to be evaluated for sources of emboli (carotid ultrasound and 2-D echo of heart) or inflammatory conditions such as giant cell arteritis to prevent future strokes.