Cotton-Wool Spots

Fluffy white patches on the retina seen during a dilated eye exam. They reflect small areas of nerve fiber damage and have many possible causes.

8 min read

Cotton-wool spots are small, fluffy white patches that appear on the retina during a dilated eye exam. They are not a disease by themselves - they are a sign of focal retinal nerve fiber layer injury, usually from impaired small-vessel blood flow and interrupted axoplasmic transport. The list of conditions that produce cotton-wool spots is long, and many patients with one or two of them have an underlying systemic cause that needs identifying.

Key Takeaways

Cotton-wool spots are focal infarcts of the retinal nerve fiber layer, caused by occlusion of small precapillary arterioles, seen clinically as fluffy white opacities
They appear and disappear - most resolve over 6 weeks to several months as the swelling clears (sometimes 6-9 months in diabetes), often leaving subtle nerve fiber loss behind
The most common causes are diabetes and hypertension, but cotton-wool spots also occur in many systemic and ocular diseases
A single isolated cotton-wool spot in an otherwise healthy patient still warrants a focused check for diabetes, hypertension, blood disorders, and embolic risk when the pattern or history suggests it
They are usually painless and do not affect vision unless they are central or numerous

What Cotton-Wool Spots Look Like

On the dilated fundoscopic exam, cotton-wool spots appear as:

Small, fluffy, white patches with feathery indistinct edges
Typically 100-300 microns across (small fractions of a millimeter)
Superficial - they obscure the underlying retinal blood vessels rather than lying beneath them
Located in the posterior pole, around the optic nerve and macula, where the nerve fiber layer is thickest
Usually not associated with hemorrhage in their immediate vicinity, although hemorrhages may coexist elsewhere

OCT of a cotton-wool spot shows hyperreflective thickening of the retinal nerve fiber layer that gradually thins as the spot resolves, often leaving a depression in the nerve fiber layer where it used to be.

What Causes a Cotton-Wool Spot

Cotton-wool spots are focal infarcts of the retinal nerve fiber layer caused by occlusion of small precapillary arterioles. The infarcted axons stop transporting their normal contents, swell, and become opaque - what the doctor sees as a fluffy white spot.

Anything that compromises small retinal arteriolar perfusion can produce them:

Vascular and Systemic

Diabetic retinopathy - the most common cause; cotton-wool spots are part of moderate to severe nonproliferative disease
Hypertensive retinopathy - especially with malignant or accelerated hypertension; pre-eclampsia in pregnancy
Retinal vein occlusion - both central and branch; usually multiple cotton-wool spots in the territory
Retinal arterial occlusive disease - small embolic events to precapillary arterioles can produce cotton-wool spots, and CWS may accompany BRAO or CRAO at the boundary of the infarct. Deeper retinal ischemia (paracentral acute middle maculopathy, PAMM) is a related but distinct entity affecting the middle retinal layers

Embolic

Carotid embolic disease - including Hollenhorst plaques (cholesterol emboli)
Cardiac embolism - endocarditis, atrial fibrillation, valve disease
Talc retinopathy - IV drug use with crushed oral pills
Fat embolism after long-bone fracture

Inflammatory and Autoimmune

Lupus retinopathy - cotton-wool spots can be a sign of active SLE in the eye
Vasculitides - granulomatosis with polyangiitis, polyarteritis nodosa
Antiphospholipid syndrome

Infectious

HIV retinopathy - the most common ocular finding in HIV. Cotton-wool spots reflect HIV-associated microvasculopathy from immune complex deposition, hyperviscosity, and direct endothelial effects of the virus rather than opportunistic infection of the retina
Cytomegalovirus retinitis - in immunosuppression
Other systemic infections - sepsis, severe COVID-19

Hematologic and Hyperviscosity

Severe anemia
Leukemia - Roth spots (retinal hemorrhages with a pale center; in leukemia the center is a focal leukemic infiltrate) can coexist with cotton-wool spots
Multiple myeloma and other paraproteinemias

Other

Radiation retinopathy - typically months to years after orbital or paranasal radiotherapy
Purtscher and Purtscher-like retinopathy - after major chest trauma, acute pancreatitis, or amniotic fluid embolism; characterized by multiple cotton-wool spots and intraretinal hemorrhages
High-altitude retinopathy
Interferon-associated retinopathy

What a Cotton-Wool Spot Means for the Patient

A single cotton-wool spot rarely produces noticeable vision change unless it sits exactly at the fovea - and even then, the visual effect is usually a small paracentral scotoma rather than a global change. Patients usually do not feel a cotton-wool spot. The spot itself is not the problem; it is a marker that small-vessel circulation has been compromised somewhere, and the diagnostic value is in finding out why.

What Happens to a Cotton-Wool Spot Over Time

Cotton-wool spots are dynamic. The typical sequence is:

Acute - sudden appearance of one or several fluffy white patches over hours to days
Stabilization - the spot does not enlarge much after the initial event
Resolution - gradual fading over 6 weeks to several months as the swollen axoplasmic material is cleared by the retina (resolution can take 6-9 months in diabetic patients)
Residual nerve fiber thinning - a faint depression in the nerve fiber layer at the site, sometimes detectable on OCT or as a subtle visual field defect

A persistent or enlarging cotton-wool spot, or new spots appearing during follow-up, suggests ongoing disease rather than a single past event.

How a Cotton-Wool Spot Drives Workup

Even one cotton-wool spot in an otherwise asymptomatic adult deserves at least a focused systemic evaluation:

Vital signs - blood pressure, including check for malignant or pregnancy-related hypertension
Blood tests - fasting glucose or HbA1c (diabetes), CBC (anemia, leukemia, hyperviscosity), basic chemistry, lipid panel
Inflammatory markers - ESR, CRP, ANA, antiphospholipid panel if autoimmune disease suspected
HIV and other infectious testing when the clinical context supports it
Carotid ultrasound and echocardiography if embolic disease is suspected, particularly with multiple unilateral spots

Multiple cotton-wool spots, or asymmetric distribution, push the workup toward systemic vasculitis, embolic disease, and high-grade hypertension or diabetes.

How Cotton-Wool Spots Differ from Similar-Looking Findings

Finding	Appearance	Key feature
Cotton-wool spot	Small fluffy white patch	Superficial; obscures underlying vessels; resolves over weeks
Hard exudate	Discrete, sharp-edged yellow deposit	Lipid; deeper; persistent; often around macula in diabetes
Drusen	Small yellow round deposits	Within Bruch's membrane; not infarctive; chronic
Roth spot	Retinal hemorrhage with a pale center	Pale center is a fibrin-platelet plug or, in leukemia, a focal leukemic infiltrate; causes include bacterial endocarditis, leukemia, severe anemia, hypoxia, and HIV
Myelinated nerve fibers	White patch radiating from disc	Congenital; follows nerve fiber direction; not infarctive
Cytomegalovirus retinitis lesion	White patch with adjacent hemorrhage	Larger, expands over time; immunosuppressed patient

What the Patient Notices

Most patients learn they have a cotton-wool spot only because their doctor mentions it. Symptoms, when present, are subtle:

A small, fixed, paracentral blind spot if the spot is near the fovea
Slight blurring of small text in the affected area
Usually no pain and no photophobia

If the cotton-wool spot is part of a larger systemic event - for example, a retinal artery occlusion or hypertensive crisis - the broader presentation is what brings the patient to attention rather than the spot itself.

Frequently Asked Questions

Will the cotton-wool spot go away?

Usually yes, over weeks to several months (sometimes 6-9 months in diabetes). The spot itself fades, but a small area of nerve fiber loss often remains. This residual thinning rarely produces noticeable symptoms unless many spots have accumulated over time.

Why did my eye doctor send me to my primary care doctor after seeing a cotton-wool spot?

Because the most common causes of a cotton-wool spot - diabetes and hypertension - are systemic problems, not eye problems. The eye is the window where the issue is first visible, but managing the underlying cause prevents future spots and protects the rest of your body, including your kidneys, heart, and brain.

Is a cotton-wool spot the same as a stroke in the eye?

Not the same, but related. A cotton-wool spot is a tiny ischemic-appearing nerve fiber layer lesion, while a retinal artery occlusion is a much larger event with substantial vision loss. Both can reflect compromised retinal blood flow, which is why finding a cotton-wool spot prompts a check for vascular risk factors.

Can I have a cotton-wool spot without diabetes or hypertension?

Yes. Cotton-wool spots can occur with autoimmune disease (especially lupus), HIV, embolic disease from the carotids or heart, anemia, leukemia, severe infection, and a number of less common conditions. Your doctor will narrow the differential based on your other history and exam findings.

Are cotton-wool spots dangerous?

The spots themselves are usually not visually dangerous unless they sit centrally or are very numerous. Their importance is what they signal - an underlying condition that, if untreated, can produce more serious eye and systemic problems over time.

References

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