Webster Dictionary(0.00 / 0 votes)Rate this definition: Freebase(0.00 / 0 votes)Rate this definition: Crenulation or Crenulation cleavage is a texture formed in metamorphic rocks such as phyllite, schist and some gneiss by two or more stress directions resulting in superimposed foliations.
Retinal vein occlusions typically occur in older patients with a history of high blood pressure and atherosclerosis. Other causes of retinal vein occlusion include vasculitis, clotting disorders, and medications such as oral contraceptive pills.
Several factors combine to bring on an occlusion. The usual situation is that the blood flow in a retinal vein is slowed down and a clot forms. The clot prevents blood from flowing freely. The blood is back logged and spills into the retina. The most common reason for slowed venous blood flow is a hardened artery (arteriosclerosis).