Cotton wool spots
Cotton wool spots are an abnormal finding on funduscopic exam of the retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

 of the eye. They appear as puffy white patches on the retina. They are caused by damage to nerve fibers. The nerve fiber
Nerve fiber
A nerve fiber is a threadlike extension of a nerve cell and consists of an axon and myelin sheath in the nervous system. There are nerve fibers in the central nervous system and peripheral nervous system. A nerve fiber may be myelinated and/or unmyelinated. In the central nervous system , myelin...

s are damaged by swelling in the surface layer of the retina. The cause of this swelling is due to the reduced axonal transport (and hence backlog of intracellular products) within the nerves because of the ischemia.

Diabetes and hypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...

 are the two most common diseases that cause these spots, and the best treatment would be to treat the underlying disease. In diabetes they are one of the hallmarks of pre-proliferative retinopathy
Diabetic retinopathy
Diabetic retinopathy is retinopathy caused by complications of diabetes mellitus, which can eventually lead to blindness....

. More rarely, HIV and pancreatitis (Purtscher) retinopathy can also lead to the appearance of cotton wool spots.
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