Pars planitis is a chronic type of eye inflammation that targets the middle layer of the eye, specifically a region called the pars plana, which sits just behind the lens. It belongs to a broader category called intermediate uveitis but is distinguished by being idiopathic, meaning it has no identifiable underlying cause. The condition predominantly affects children and adolescents, accounting for 5 to 27% of pediatric uveitis cases.
Where the Inflammation Occurs
The eye has three layers. The outermost is the white sclera, the innermost is the retina, and sandwiched between them is the uvea, a pigmented layer rich in blood vessels. The uvea has three zones: the iris at the front, the choroid at the back, and the ciliary body in the middle. The pars plana is the flat rear portion of the ciliary body, sitting near the junction where the retina begins.
When this area becomes inflamed, immune cells spill into the vitreous, the gel-like substance that fills the center of the eye. Over time, these cells can clump together into visible formations that eye doctors use to identify the disease.
Snowballs and Snowbanks
Two hallmark findings set pars planitis apart from other forms of eye inflammation. The first is snowballs: yellow-white, globe-shaped clumps of inflammatory cells that float in the vitreous near the far edge of the retina. These appear in nearly all cases of intermediate uveitis.
The second finding is snowbanking. When snowballs accumulate and fuse, they form sheet-like membranes made of collagen and other structural cells that drape over the pars plana. Snowbanks typically start along the bottom of the eye and can spread upward over time. Up to 65% of intermediate uveitis cases develop snowbanks. The presence of snowballs or snowbanks, in the absence of any identifiable systemic disease, is what defines pars planitis specifically.
Symptoms Are Often Subtle
Unlike many forms of eye inflammation, pars planitis usually does not cause pain or light sensitivity. Most people notice floaters, those drifting spots or threads in their field of vision, or a gradual blurring. Because the symptoms are mild, the condition sometimes goes undetected for months or longer, especially in young children who may not articulate changes in their vision. In some cases, it’s discovered incidentally during a routine eye exam.
What Causes It
By definition, pars planitis is idiopathic. If a doctor identifies a systemic condition driving the inflammation, the diagnosis shifts from pars planitis to intermediate uveitis associated with that condition. That said, eye doctors will typically run tests to rule out diseases that can mimic the same pattern of inflammation, including multiple sclerosis, sarcoidosis, and certain infections. The workup exists not because these conditions cause pars planitis, but because they can produce similar-looking inflammation in the same part of the eye, and the treatment would be different.
Complications to Watch For
The inflammation itself may be quiet, but left untreated, pars planitis can damage surrounding structures. In a long-term study of over 100 eyes, the most common complications were:
- Cystoid macular edema: fluid buildup in the central retina that blurs fine detail vision, occurring in about 8% of eyes
- Cataracts: clouding of the lens significant enough to affect vision, seen in roughly 15% of eyes
- Epiretinal membrane: a thin layer of scar tissue forming on the retina’s surface
- Retinal detachment: the retina pulling away from the back of the eye, occurring in about 8% of eyes
- Abnormal blood vessel growth: new, fragile vessels that can bleed into the vitreous, found in about 7% of eyes
Cystoid macular edema is the leading cause of vision loss in pars planitis. It can develop even when the eye looks relatively calm on the surface, which is why regular monitoring with imaging scans is a standard part of follow-up care.
How It’s Treated
Treatment follows a stepwise approach based on severity. Mild cases with good vision and minimal inflammation may only need close monitoring. When treatment is needed, the first step is typically corticosteroids delivered around or into the eye to calm the immune response locally.
If the inflammation doesn’t respond to steroids, or if the disease is already advanced at the time of diagnosis, doctors add longer-term immune-suppressing medications. In a study of 49 patients at a referral center, about half started steroids before adding these medications, while the other half began both at the same time. Visual outcomes were similar regardless of timing, suggesting that early combination therapy is a reasonable option for more aggressive disease.
For eyes with significant snowbanking, cryotherapy (a freezing treatment applied to the pars plana) can be effective. In one study, all 12 eyes treated with cryotherapy within three months of symptom onset, when the snowbank was still relatively small, maintained 20/25 vision or better. Eyes treated later or with larger snowbanks had less consistent results, highlighting the value of early intervention.
Long-Term Outlook
With appropriate treatment, most people with pars planitis retain good vision. A study of children with the condition found that average final visual acuity reached 20/24, with improvement in 73% of eyes over an average follow-up of four years. Some patients achieved full remission after stopping treatment, while others remained disease-free on maintenance therapy.
Pars planitis is a chronic condition, and flare-ups can recur over years. The goal of treatment is to keep inflammation suppressed long enough to prevent cumulative damage, particularly to the macula. Regular follow-up exams, often every few months during active disease and less frequently during remission, are essential for catching complications early and adjusting treatment before vision is affected.