Cotton wool spots are small, whitish, fluffy-looking patches on the retina, the light-sensitive tissue at the back of your eye. They form when tiny blood vessels supplying the retina become blocked, cutting off blood flow to the nerve fibers that carry visual signals to the brain. They’re not a disease on their own but rather a visible sign that something else is affecting your blood vessels, most commonly high blood pressure or diabetes.
What Causes Them to Form
The retina’s innermost layer contains long nerve fibers (axons) that constantly shuttle nutrients and cellular material back and forth between the eye and the brain. This transport system runs in both directions and keeps nerve cells healthy. When a small blood vessel gets blocked, the nerve fibers in that area lose their blood supply, and this transport system stalls. Cellular debris piles up at the edges of the blocked zone, much like cars backing up behind a road closure.
That buildup of trapped material inside the swollen nerve fibers is what creates the characteristic white, fluffy appearance you see on a retinal exam. The spots typically show up near the optic disc or along the major blood vessel pathways on the retina, where nerve fiber density is highest.
Conditions That Cause Cotton Wool Spots
Because cotton wool spots result from disrupted blood flow, they show up across a range of conditions that damage small blood vessels. The two most common are:
- High blood pressure. Cotton wool spots appear in moderate to severe hypertensive retinopathy. In the standard grading system for hypertensive eye damage, their presence (along with retinal hemorrhages) marks Grade 3 disease, indicating that blood pressure has been high enough to cause visible retinal injury.
- Diabetes. Cotton wool spots can appear early in diabetic retinopathy, sometimes as one of the first visible signs of retinal damage, even before more advanced changes develop. Research has documented cases where a few small cotton wool spots were the only finding, or appeared alongside fewer than 10 microaneurysms.
Other conditions linked to cotton wool spots include lupus and other autoimmune diseases, blood disorders like severe anemia, and HIV. In HIV-positive patients with significantly weakened immune systems, roughly 8 to 12 percent develop cotton wool spots. They have also been observed in patients with COVID-19. Occasionally, a cotton wool spot appears in isolation in an otherwise healthy person with no identifiable cause.
What They Look Like on an Eye Exam
During a dilated eye exam, cotton wool spots appear as small white or yellowish-white patches with soft, feathery edges. They sit in the superficial layers of the retina, which distinguishes them from hard exudates, the other common “bright spot” found on retinal exams. Hard exudates are deposits of leaked fats and proteins. They tend to have sharper, more well-defined borders and a waxy yellow appearance. Cotton wool spots, by contrast, look more diffuse and cloud-like.
If your eye doctor uses optical coherence tomography (OCT), a scan that produces cross-sectional images of the retina, a cotton wool spot shows up as a bright, thickened area in the inner retinal layers, particularly the nerve fiber layer and ganglion cell layer. The swelling can be prominent enough to distort the layers beneath it. As the spot resolves, the bright signal shrinks and eventually leaves behind a thin area where the nerve tissue has atrophied slightly.
Do They Affect Vision?
A single cotton wool spot rarely causes noticeable vision changes on its own. Each one is small, typically covering a limited patch of retina. You might have a tiny blind spot in the corresponding area of your visual field, but most people never notice it. The bigger concern is what the spots represent: if they’re appearing because of uncontrolled blood pressure or worsening diabetes, those underlying conditions can cause progressive and more serious vision loss over time if left untreated.
How Long They Last
Cotton wool spots are temporary. When the underlying cause is treated or controlled, they typically fade within 6 to 12 weeks. On OCT imaging, you can watch this process unfold: the bright, swollen area gradually shrinks, the distorted retinal layers return to their normal positions, and eventually only a subtle thinning of the inner retina remains where the spot once was. That mild thinning reflects a small, permanent loss of nerve fibers in the area, but it’s rarely enough to produce a noticeable visual deficit.
What Happens After They’re Found
When an eye doctor spots cotton wool spots during a routine exam, the priority is figuring out why they’re there. If you don’t already have a diagnosis of diabetes, high blood pressure, or another associated condition, expect a workup that includes blood pressure measurement, blood sugar testing, and potentially blood work to check for autoimmune markers or blood disorders.
The cotton wool spots themselves don’t need direct treatment. They resolve on their own once the underlying problem is managed. What matters is addressing the root cause: getting blood pressure under control, tightening blood sugar management, or treating whatever systemic condition is driving the vascular damage. The spots serve as an important early warning that small blood vessels throughout your body, not just in your eyes, may be under stress.