Coats disease affects roughly 1.7 out of every 100,000 people, making it a genuinely rare condition. To put that in perspective, in a city of 100,000 residents, you’d expect to find only one or two people with it. The disease causes abnormal blood vessels in the retina to leak fluid and fatty deposits, gradually threatening vision in the affected eye.
Prevalence by Age and Sex
Coats disease strongly favors males. About 72 to 76 percent of patients are male, creating a roughly 3:1 male-to-female ratio. Among children under 20, the prevalence is notably higher than in adults: 3.6 per 100,000 compared to 1.3 per 100,000 for adults. Boys under 20 are the most commonly affected group, with a prevalence of 5.7 per 100,000, while girls of the same age come in at 1.5 per 100,000.
The classic form of the disease appears in young boys around age 6 to 8. Adult-onset Coats disease does exist but is rarer, typically showing up after age 35 and generally running a milder course than the childhood version.
Reported rates vary by country. A UK study found an incidence of just 0.09 per 100,000, while an Indian study reported a much higher prevalence of 25.3 per 100,000. These differences likely reflect variation in diagnostic access, screening practices, and study methods rather than true biological differences between populations.
What Causes It
Most cases of Coats disease are sporadic, meaning they appear without any family history or identifiable inherited cause. In rare instances, a mutation in the NDP gene on the X chromosome has been linked to the condition. This gene produces a protein called norrin, which helps regulate how blood vessels grow in the retina. When the gene doesn’t function properly, retinal blood vessel development goes wrong. Only one published case has directly connected Coats disease to an NDP mutation in a family, so genetic forms are exceptionally uncommon even within this already rare disease.
The condition affects only one eye in about 95 percent of cases. The abnormal retinal blood vessels become dilated and leaky, allowing fluid and lipid-rich deposits to accumulate beneath and within the retina. Over time, this buildup can cause the retina to detach.
How It’s Usually Discovered
The first sign depends partly on the child’s age and how far the disease has progressed. In one study of affected eyes, 50 percent presented with decreased vision, 27 percent with strabismus (eyes not aligning properly), and 23 percent with leukocoria, a white or yellowish reflection in the pupil that parents sometimes notice in photographs.
That white pupil reflex creates a diagnostic challenge. Leukocoria is also the hallmark sign of retinoblastoma, a childhood eye cancer, and Coats disease is the single most common condition mistaken for it. Among children referred with suspected retinoblastoma, 16 to 22 percent turn out to have something else. Of those lookalike conditions, Coats disease accounts for about 40 percent. This overlap matters because 5 to 12 percent of eyes surgically removed for suspected retinoblastoma turn out on pathology to have been a noncancerous condition. Accurate imaging and careful evaluation help avoid unnecessary eye removal.
Stages of Progression
Coats disease is classified into five stages based on what’s happening inside the eye:
- Stage 1: Abnormal blood vessels are visible in the retina, but they haven’t started leaking yet.
- Stage 2: The vessels begin leaking fluid and fatty deposits. Stage 2A means the leakage is away from the center of vision; Stage 2B means it has reached the fovea, the part of the retina responsible for sharp central sight.
- Stage 3: Enough fluid has accumulated to partially or fully detach the retina.
- Stage 4: The retina is completely detached and pressure inside the eye has risen (glaucoma).
- Stage 5: End-stage disease with irreversible damage.
Not every case progresses through all stages. Some remain stable at early stages for years, particularly in adults, whose disease tends to advance more slowly.
Treatment Outcomes
When caught early, the outlook is encouraging. In a long-term pediatric study, the overall rate of saving the eye (avoiding removal) was 92.2 percent. The key is catching the disease before it reaches the advanced stages.
Several factors predict a worse outcome. Eyes with disease affecting all four quadrants of the retina, those that develop cataracts, and those with scarring or fibrous tissue forming in or beneath the retina face higher risks of losing the eye. For preserving useful vision specifically, the most important factors are whether the center of the retina has been scarred and whether the child follows through with amblyopia therapy (patching the stronger eye to strengthen the weaker one). Even after successful treatment of the retinal disease itself, visual rehabilitation plays a major role in the final level of sight a child achieves.
Adults with Coats disease generally have a less aggressive course. The disease tends to progress more slowly, and painful complications like elevated eye pressure are less common than in children, though vision loss in the affected eye remains a real possibility without monitoring and treatment.