Pars planitis is a rare type of inflammation inside the eye, mainly affecting the gel-like substance near the retina and a nearby area called the pars plana. It can cause floaters—small spots or threads in your vision—and blurred sight. It often has no clear cause. An eye specialist diagnoses it after examining the eye and checking for other possible causes of inflammation.
Where does pars planitis occur in the eye?
Pars planitis is a form of intermediate uveitis. Uveitis refers to inflammation inside the eye, while intermediate uveitis mainly affects the vitreous, the clear, gel-like substance that fills the space between the lens and the retina, and nearby structures.
The pars plana is a part of the ciliary body, a structure located behind the iris, the colored part of the eye. Inflammation in this area can release inflammatory cells and other material into the vitreous, making it harder for light to pass through clearly and potentially affecting vision.
According to the National Institutes of Health Genetic and Rare Diseases Information Center, pars planitis can be associated with blurred vision, floating spots, and complications such as cataracts, retinal detachment, or macular edema. Macular edema means swelling caused by fluid collecting in the macula, the part of the retina responsible for detailed central vision.
What symptoms can pars planitis cause?
Pars planitis may develop gradually, and some people initially notice only small changes in their sight. The inflammation can also be present before a person recognizes a clear visual problem. Symptoms that may occur include:
- Floaters: Small dots, dark specks, threads, or cobweb-like shapes that seem to move across the field of vision.
- Blurred or hazy vision: Objects may appear less clear because inflammatory material clouds the vitreous.
- Reduced visual clarity: Vision may become more difficult when the inflammation or its complications affect the retina.
- Few noticeable symptoms: Some people have little discomfort, and eye inflammation may be found during an examination rather than because of obvious symptoms.
Eye pain, redness, and sensitivity to light are not prominent features in many cases, although other forms of eye inflammation can cause them. In children, visual difficulties may be harder to recognize because a child may not be able to explain changes in sight clearly.
When should changes in vision be checked urgently?
Arrange an eye examination if floaters or blurred vision are new, persistent, or getting worse. Seek urgent medical assessment if you experience a sudden increase in floaters, flashes of light, a dark curtain or shadow across your vision, or sudden blurring or loss of sight. These changes can indicate a retinal tear or retinal detachment, which requires prompt assessment and may threaten vision. The NHS guidance on retinal detachment explains why these symptoms should not be ignored.
What causes pars planitis?
In many cases, the exact cause of pars planitis is unknown. An abnormal immune response has been proposed as a possible explanation, but the underlying process has not been fully established. The term idiopathic is used when a specific cause cannot be identified.
Pars planitis is a particular subtype of intermediate uveitis in which characteristic inflammatory deposits are present and no underlying infection or associated systemic disease is identified. Other conditions can cause similar inflammation inside the eye, so clinicians may investigate for infections or inflammatory disorders when the examination or medical history makes them relevant.
The National Library of Medicine's StatPearls clinical review of pars planitis describes the cause as uncertain and explains why clinicians need to distinguish this condition from other possible causes of intermediate uveitis. Identifying an underlying condition matters because the appropriate treatment may differ.
How is pars planitis diagnosed?
An ophthalmologist, preferably one experienced in uveitis when specialist care is needed, evaluates the eye and considers the person's symptoms, medical history, and examination findings. There is no single blood test that confirms pars planitis. Diagnosis depends mainly on the pattern of inflammation seen during a detailed eye examination and on excluding other conditions that could explain the findings.
Which eye examinations may be used?
- Dilated eye examination: Eye drops widen the pupils so the ophthalmologist can examine the retina and the outer areas of the back of the eye.
- Slit-lamp examination: A specialized microscope helps the clinician examine structures at the front of the eye and assess signs of inflammation.
- Optical coherence tomography (OCT): This scan produces detailed images of the retina and can help detect macular edema or other structural changes.
- Retinal imaging or angiography: Additional imaging may be used when the clinician needs to assess inflammation affecting retinal blood vessels or look for complications.
During the examination, the ophthalmologist may see small clusters of inflammatory cells in the vitreous, sometimes called snowballs, or pale inflammatory deposits along the pars plana, sometimes called snowbanks. These are descriptive terms for findings inside the eye, not symptoms a person can reliably identify themselves.
Depending on the findings, further tests may be recommended to look for infections or systemic inflammatory conditions. The EyeWiki clinical reference on intermediate uveitis describes the importance of evaluating these alternative causes before deciding on treatment.
How is pars planitis treated?
Treatment depends on how active the inflammation is, whether vision is affected, and whether complications have developed. Not every person needs immediate medication. When inflammation is limited and vision remains good, an ophthalmologist may recommend regular monitoring. Active inflammation that threatens vision or causes complications generally requires treatment to control the inflammatory process.
Medicines to control inflammation
Corticosteroids are commonly used to reduce inflammation when treatment is needed. Depending on the location and extent of the inflammation, they may be given by injection around the eye, injection inside the eye, or oral medication. These treatments require medical supervision because corticosteroids can cause problems such as increased eye pressure and cataracts.
If inflammation persists, returns repeatedly, or requires prolonged treatment, an eye specialist may consider steroid-sparing medicines that modify the immune response. The choice depends on the individual's condition, previous treatment, and potential medication risks. These medicines are not suitable for everyone and may require additional monitoring.
When might a procedure or surgery be needed?
Procedures are considered when medication does not adequately control the inflammation or when particular complications need attention. In selected cases, treatment may involve laser therapy, cryotherapy, which uses freezing to treat specific areas of tissue, or vitrectomy, an operation that removes some of the vitreous gel. These options are not necessary for everyone with pars planitis.
Can pars planitis affect vision over time?
The course of pars planitis differs from person to person. Some people maintain useful vision with observation or treatment, while others develop recurring inflammation or complications that require additional care. Regular examinations help the ophthalmologist assess whether inflammation is active, check for changes in vision, and adjust the treatment plan when necessary.
Possible complications include macular edema, cataracts, increased eye pressure or glaucoma, abnormal growth of retinal blood vessels, bleeding inside the eye, and retinal detachment. A peer-reviewed review available through the National Library of Medicine's PubMed Central identifies macular edema as an important cause of vision problems in pars planitis and discusses other complications associated with long-term inflammation.
Children and adolescents can develop pars planitis as well as adults. In children, prolonged inflammation or reduced vision can interfere with normal visual development and may contribute to amblyopia, sometimes called lazy eye. Pediatric cases therefore need appropriate ophthalmic follow-up, even when symptoms are difficult for the child to describe.
What should you expect during follow-up?
Follow-up visits allow the ophthalmologist to monitor inflammation, measure vision, assess the retina, and check for treatment-related side effects. The timing depends on disease activity, current medication, and whether complications are present. Some people need more frequent appointments during active inflammation, while those whose condition is stable may be reviewed less often.
Report new or worsening visual symptoms promptly rather than waiting for a scheduled appointment. Keeping follow-up visits and using prescribed medicines exactly as directed help the care team respond to changes and protect vision over time.