Pars Planitis: Chronic Eye Inflammation Explained
Understanding Pars Planitis
Pars planitis is a type of intermediate uveitis (inflammation of the middle layer of the eye). It specifically involves the pars plana, a flat zone near the front edge of the retina. The condition is considered idiopathic, meaning its exact cause is unknown. However, the immune system is believed to play a central role.
The Standardization of Uveitis Nomenclature (SUN) Working Group published classification criteria in 2021. Under these criteria, pars planitis is defined as idiopathic intermediate uveitis that includes either vitreous snowballs or pars plana snowbanks.
Two hallmark signs help a retina specialist identify pars planitis. Snowbanks are whitish deposits of fibrous tissue that form along the lower part of the pars plana. They are made up of immune cells, vitreous collagen, and other cell types. Snowballs are clumps of inflammatory cells that float in the vitreous (the clear gel that fills the inside of the eye). Both signs point to ongoing inflammation.
The inflammation in pars planitis is driven by the immune system. A specific type of white blood cell called a CD4+ T cell plays a major role. These cells account for up to 95% of all immune cells found in the vitreous of affected patients (Survey of Ophthalmology, 2010). The immune system appears to react to an unknown substance inside the eye. This causes chronic inflammation in the vitreous and the small blood vessels at the edge of the retina, a process called peripheral retinal vasculitis.
Who Is Affected and Risk Factors
Pars planitis most commonly affects people between the ages of 15 and 40, though it can appear in younger children as well. The incidence in the United States is approximately 2.08 per 100,000 persons (American Journal of Ophthalmology, 2008). There is no clear preference for one gender or race over another. However, research has shown that Hispanic children may have a lower prevalence of the condition compared to non-Hispanic children, at 9.6% versus 19.2% (PMC, 2016).
Although pars planitis is idiopathic, genetics appear to increase susceptibility. Certain immune system markers called human leukocyte antigens (HLAs) have been linked to the disease. These include HLA-B51, HLA-DR2, HLA-DR15, and HLA-DRB1*0802. Having one of these markers does not mean a person will develop pars planitis, but it may raise the risk.
Pars planitis has been associated with several other medical conditions. Research shows that 8% to 16% of patients with pars planitis may also have or develop multiple sclerosis (American Journal of Ophthalmology, 2008). Approximately 11.1% of patients have a first-degree relative with MS. Sarcoidosis, an inflammatory disease that can affect multiple organs, is found in about 22% of cases (American Journal of Ophthalmology, 2008). In rare instances, fewer than 1% of cases may be linked to Lyme disease (Survey of Ophthalmology, 2010).
Pars planitis affects both eyes in 70% to 90% of cases, though the severity often differs between the two eyes (American Journal of Ophthalmology, 2008). This asymmetric pattern means one eye may have more inflammation or more complications than the other. A retina specialist will examine both eyes carefully, even if symptoms appear in only one.
Signs and Symptoms
The most frequent symptoms of pars planitis include floaters and blurred vision. Floaters may appear as small spots, threads, or cobweb-like shapes drifting across the visual field. Vision may become gradually hazy as inflammatory cells accumulate in the vitreous. Unlike some other forms of uveitis, pars planitis typically does not cause eye pain or significant redness.
One of the most concerning aspects of pars planitis is that children may show no symptoms at all despite active disease. Because young children may not notice or report subtle vision changes, the condition can go undetected for months or even years. Pars planitis accounts for 5% to 26.7% of pediatric uveitis cases, with one large multicenter study of 527 children finding it in 17.1% of cases (PMC, 2016). Regular eye exams are essential for early detection in at-risk children.
Without treatment, pars planitis can lead to progressive vision loss. About 20% of untreated patients will experience significant decline in vision over time (American Journal of Ophthalmology, 2008). Vision loss may develop gradually from chronic inflammation or suddenly from complications such as vitreous hemorrhage (bleeding inside the eye), which occurs in approximately 28% of pediatric cases.
Diagnosis and Testing
A retina specialist diagnoses pars planitis through a thorough eye examination. This includes a slit-lamp exam, which uses a special microscope and light to examine the front and middle portions of the eye. The specialist looks for cells floating in the vitreous, snowballs, and snowbanks. A dilated eye exam allows the specialist to view the peripheral retina and pars plana in detail.
Several imaging tools help confirm the diagnosis and monitor the condition. Optical coherence tomography (OCT) produces detailed cross-sectional images of the retina. It can detect swelling called cystoid macular edema (CME), a common complication. Fluorescein angiography uses a special dye and camera to reveal leaking blood vessels and peripheral retinal vasculitis. In some cases, blood tests and neurological evaluations may be ordered to rule out associated conditions such as multiple sclerosis, sarcoidosis, or Lyme disease.
Because several diseases can mimic intermediate uveitis, a retina specialist must rule out other causes before confirming pars planitis. Infections such as Lyme disease, tuberculosis, and syphilis can cause similar inflammation. Sarcoidosis and lymphoma may also present with vitreous cells. A diagnosis of pars planitis is made only when the intermediate uveitis is idiopathic and snowbanks or snowballs are present, following the 2021 SUN classification criteria.
Treatment Options
Treatment for pars planitis follows a stepladder approach. This means therapy begins with less aggressive options and escalates as needed. The goal of treatment is to control inflammation, prevent complications, and preserve vision. Not every patient requires the same level of treatment. A retina specialist will tailor the plan to the individual.
For mild to moderate cases, periocular corticosteroid injections are often the first step. Triamcinolone, a corticosteroid, is injected near the eye to reduce inflammation locally. This approach delivers medication directly to the affected area while limiting effects on the rest of the body. However, corticosteroid use carries risks including increased eye pressure and cataract formation, so patients require regular monitoring.
When both eyes are significantly affected, a retina specialist may prescribe oral corticosteroids such as prednisolone. A typical starting dose is 1 to 1.5 milligrams per kilogram of body weight per day. Systemic steroids are effective at reducing widespread inflammation, but long-term use can cause side effects. These include weight gain, bone thinning, elevated blood sugar, and increased risk of infection. These medications are usually tapered gradually once inflammation is controlled.
When corticosteroids are not sufficient or need to be reduced due to side effects, immunomodulatory agents serve as second-line treatment. These medications work by adjusting the immune system to reduce chronic inflammation. Commonly used options include methotrexate, mycophenolate mofetil, azathioprine, and cyclosporine. Each of these drugs requires regular blood testing to monitor for potential side effects affecting the liver, kidneys, or blood cells.
Adalimumab (Humira) is a biologic medication that is FDA-approved for the treatment of noninfectious intermediate, posterior, and panuveitis. This includes pars planitis. It works by blocking a specific inflammatory protein called tumor necrosis factor-alpha (TNF-alpha). Adalimumab is given as an injection under the skin, typically every two weeks. It may be recommended when standard immunomodulatory agents have not achieved adequate control.
In cases where complications develop or inflammation does not respond to medical therapy, surgical options may be considered. Pars plana vitrectomy (surgery to remove the vitreous gel) can clear inflammatory debris and snowbanks from the eye. Laser photocoagulation (thermal laser treatment) may be used to treat areas of peripheral retinal vasculitis or to manage abnormal blood vessel growth. Avastin (bevacizumab), which is FDA-approved for cancer and used off-label for eye conditions, may be injected into the eye to treat neovascularization (abnormal new blood vessel growth) that sometimes develops as a complication.
What to Expect
With appropriate treatment, the outlook for many patients with pars planitis is encouraging. Research shows that 75% of patients maintain visual acuity of 20/40 or better after 10 years of follow-up (American Journal of Ophthalmology, 2008). However, this condition is chronic and may require years of monitoring and treatment adjustments. Some patients experience periods of remission followed by flares of inflammation.
Several complications can develop from pars planitis if it is not well controlled. The most common complication is cystoid macular edema, which causes swelling in the central retina and can reduce central vision. Other possible complications include cataracts, glaucoma (increased pressure inside the eye), vitreous hemorrhage, epiretinal membrane formation (scar tissue on the retina), and retinal detachment. Pediatric patients tend to have a more aggressive disease course and a higher risk of complications compared to adults.
Because of the known association between pars planitis and multiple sclerosis, patients may need neurological evaluation. Research indicates a 16.2% risk of developing MS within five years of a pars planitis diagnosis (American Journal of Ophthalmology, 2008). This risk is higher in patients who have periphlebitis (inflammation of veins in the retina) at the time of presentation. A retina specialist may coordinate with a neurologist to monitor for neurological symptoms and, if indicated, order brain imaging.
Living with Pars Planitis
Pars planitis requires consistent follow-up with a retina specialist. Appointments may be scheduled every few weeks during active flares and every few months during periods of remission. At each visit, the specialist will check for signs of inflammation, monitor for complications, and adjust treatment as needed. Sticking to the recommended follow-up schedule is one of the most important steps patients can take to protect their vision.
Because pars planitis can affect children who may not report symptoms, parents and caregivers play a critical role. Any child diagnosed with pars planitis should have regular, scheduled eye exams with a retina specialist. Parents should watch for signs such as squinting, holding objects close to the face, or difficulty in school. Early intervention in pediatric cases can make a meaningful difference in long-term visual outcomes.
Living with a chronic eye condition can be stressful, especially for young patients and their families. Uncertainty about flares, the need for ongoing medication, and concern about vision loss can take an emotional toll. Patients may benefit from connecting with support organizations focused on uveitis or autoimmune eye disease. Open communication with a retina specialist about treatment goals, side effects, and quality of life can help patients feel more in control of their care.
When to See a Retina Specialist
Anyone experiencing new floaters, blurred vision, or a gradual decline in visual clarity should see a retina specialist for evaluation. Even if symptoms seem mild, they may indicate active inflammation that requires treatment. Patients already diagnosed with pars planitis should contact their specialist if they notice any change in their vision between scheduled appointments.
Certain symptoms require immediate attention. A sudden increase in floaters, flashes of light, a curtain or shadow over part of the vision, or sudden vision loss in one eye may indicate a serious complication such as retinal detachment or vitreous hemorrhage. See a retina specialist or go to the emergency room immediately if any of these symptoms occur. Prompt treatment can be critical in preserving vision.
Questions and Answers
Pars planitis is a chronic condition with no known method to eliminate it permanently. Treatment focuses on controlling inflammation, preventing complications, and preserving vision. Many patients achieve long periods of remission with appropriate therapy, but the disease can return. Ongoing monitoring with a retina specialist is essential even during quiet periods.
Pars planitis itself is not directly inherited. However, certain genetic markers, including HLA-DR15 and HLA-B51, have been associated with an increased susceptibility. Having a family member with autoimmune conditions or multiple sclerosis may also be relevant. A retina specialist may ask about family history as part of the evaluation process.
Uveitis is a broad term for inflammation inside the eye, classified by which part of the eye is affected. Pars planitis is a specific form of intermediate uveitis, meaning it targets the vitreous and pars plana region. Unlike anterior uveitis, which typically causes a red, painful eye, pars planitis often develops without pain or redness. Its defining features are the presence of snowbanks or snowballs in an otherwise idiopathic case of intermediate uveitis.
The duration of treatment varies widely. Some children experience remission after several years and may eventually be able to stop medication under careful supervision. Others may need ongoing or intermittent therapy into adulthood. Pediatric cases tend to be more aggressive, so close follow-up with a retina specialist is important to make timely treatment decisions and protect developing vision.
Given the documented association between pars planitis and multiple sclerosis, neurological screening may be recommended. This is especially relevant for patients who have periphlebitis at the time of diagnosis. A retina specialist may refer patients to a neurologist for evaluation, which could include brain MRI imaging. Not all patients with pars planitis will develop MS, but awareness and early detection are valuable.