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.
Retinal migraine is caused by the blood vessels to the eye suddenly constricting (narrowing), reducing the blood flow to the eye. It may be triggered by 1  : stress.2  smoking. 3  high blood pressure. 4  hormonal birth control pills.5  exercise. 6  bending over.7  high altitude.etinal migraine is caused by the blood vessels to the eye suddenly constricting (narrowing), reducing the blood flow to the eye. It may be triggered by 1  : stress. 2  smoking. 3  high blood pressure. 4  hormonal birth control pills. 5  exercise. 6  bending over. 7  high altitude.