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 artery occlusion. Retinal artery occlusion is a blockage in one of the small arteries that carry blood to the retina. The retina is a layer of tissue in the back of the eye that is able to sense light. Causes. Retinal arteries may become blocked when a blood clot or fat deposits get stuck in the arteries.
Retinal vein occlusion is blockage of one of your retinal veins, which are blood vessels that carry deoxygenated blood back to your heart. Retinal vein occlusion is also divided into two types: Central retinal vein occlusion (CRVO) is a blockage in the main vein of your retina, which is called the central retinal vein.