Fundoscopy of the right eye of a male patient with hemispheric retinal artery occlusion (HRAO). HRAO is a blockage of a branch of the main artery that supplies the retina, the light-sensitive layer at the back of the eye. Several Hollenhorst plaques (small bright areas) are seen. These are fragments of cholesterol that have dislodged from elsewhere in the body. At centre is a cherry red spot caused by fluid leaking from the damaged blood vessels. The lack of oxygen sur to the blockage results in sudden vision loss in the affected eye. The blockage is due to an underlying cause, such as high blood pressure or diabetes.