Cotton Wool Spots: Causes and Symptoms

What are cotton wool spots?

Cotton wool spots (CWS) are fluffy white or yellow spots that can appear on the retina. While the spots themselves don’t typically cause problems, they often indicate an underlying condition. A CWS can be a cause for concern in an otherwise healthy individual.

What causes cotton wool spots?

Cotton wool spots are likely caused by reduced blood flow (ischemia) to the retina. The retina is a layer of tissue at the back of the eye. It transforms light into nerve signals, which are then sent to the brain.

A block in the artery that brings blood to the retina may cause the ischemia that creates a CWS. Cotton wool spots are made up of swollen debris from local cells.

There are multiple conditions that can lead to the development of cotton wool spots. These fall into the following categories:

• Ischemic – conditions that prevent adequate blood flow to certain areas

• Immune and inflammatory – conditions in which the immune system mistakenly attacks the body

• Infectious – conditions caused by organisms like viruses and bacteria

• Embolic – conditions caused by a physical block in an artery, called an embolism

• Neoplastic – conditions that involve abnormal masses of tissue that are sometimes cancerous

• Medication-induced – conditions brought on by medications

• Traumatic – conditions caused by a physical injury

• Idiopathic – conditions with an unknown cause

The two conditions most frequently associated with cotton wool spots are high blood pressure (hypertension) and diabetes.

SEE RELATED: Anemia and Eyes

Hypertension and cotton wool spots

Hypertension is a condition in which blood pushes against the arteries with too much force. Long-term high blood pressure can lead to hypertensive retinopathy. This occurs when retinal blood vessels are damaged. The longer an individual’s blood pressure is high — and the higher the pressure is — the worse the damage.

In many cases, changes in the appearance of retinal blood vessels, cotton wool spots and flame hemorrhages are the first signs of hypertensive retinopathy. Flame hemorrhages consist of blood that has escaped from a blood vessel. This blood often looks like feathers or flames.

Hypertension can also impact the eyes in other ways:

• Poor blood flow can damage the nerves

• The arteries that supply blood to the eyes may become blocked

• The veins that carry blood away from the eyes may become blocked

Diabetes and cotton wool spots

Diabetes is a condition in which an individual’s blood sugar is too high for too long. The sugar can damage blood vessels anywhere in the body. If the blood vessels that lead to the retina are damaged, the vessels may release blood (hemorrhage) or plasma (edema). They may also deform (micro-aneurysm), become abnormal (intraretinal microvascular abnormalities), or start to grow (neovascularization). This is a condition known as diabetic retinopathy. 

Diabetic retinopathy won’t always show immediate symptoms. However, cotton wool spots can be an early indicator that this condition is present.

Any form of diabetes can cause diabetic retinopathy. In turn, diabetic retinopathy can result in: