Intermediate Uveitis & Pars Planitis

Overview

Intermediate uveitis is inflammation centered predominantly on the vitreous and pars plana, the anatomic region between the iris/ciliary body and the peripheral retina/choroid. Pars planitis is the term used specifically for the idiopathic subtype of intermediate uveitis characterized by the presence of snowballs (vitreous inflammatory aggregates) and snowbanks (organized exudate over the pars plana/ora serrata).²

Epidemiology & Risk Factors

Intermediate uveitis is relatively rare but occurs globally and typically affects adult females, though pediatric cases are well recognized and important to distinguish given differing management thresholds.² Etiology can be infectious, associated with a systemic disease (most notably multiple sclerosis and sarcoidosis), neoplastic (including intraocular lymphoma masquerading as uveitis), or idiopathic — with the idiopathic form termed pars planitis.²

Pathophysiology

Intermediate uveitis reflects immune-mediated inflammation of the peripheral retinal vasculature, vitreous base, and pars plana, resulting in vitreous cellular infiltration, vascular leakage evident on fluorescein angiography, and, in pars planitis, characteristic organized inflammatory exudates (snowbanking) along the inferior ora serrata. The precise immunologic trigger in idiopathic pars planitis remains incompletely understood, in contrast to the clearer immunologic or infectious mechanisms underlying secondary intermediate uveitis associated with systemic disease.

Clinical Presentation

Patients typically present with floaters and blurred vision, often without the pain, redness, or photophobia characteristic of anterior uveitis, since the inflammation is centered posteriorly. Awareness of this presentation and a dilated fundus examination in any patient presenting with new floaters is essential to the diagnosis, since intermediate uveitis can otherwise be missed on a superficial anterior segment exam alone.²

Exam Findings

• Vitreous cells and haze on dilated exam, often most prominent inferiorly
• Snowballs: discrete white-yellow vitreous inflammatory aggregates
• Snowbanking: organized, confluent exudate along the inferior pars plana/ora serrata, a relatively specific finding for pars planitis
• Retinal vascular leakage and optic nerve head leakage on fluorescein angiography, correlating with disease activity and treatment decisions
• Cystoid macular edema, the most common vision-threatening complication
• Mild anterior chamber cell may be present but is not the dominant feature

Differential Diagnosis

• Infectious causes of vitritis (syphilis, tuberculosis, Lyme disease, and others), which must be excluded before labeling disease as idiopathic pars planitis
• Sarcoidosis-associated intermediate uveitis (may have additional systemic or other ocular findings)
• Multiple sclerosis-associated intermediate uveitis (consider in patients with neurologic symptoms or MRI findings)
• Intraocular lymphoma, an important masquerade syndrome, particularly in older patients with atypical or treatment-resistant vitritis
• Other causes of posterior segment inflammation with vitreous involvement (e.g., posterior uveitis or panuveitis with prominent vitreous spillover)

Management

Diagnostic workup should include a structured review of systems and focused imaging and laboratory testing to exclude infectious and neoplastic masquerades, since PCR testing of intraocular fluid has enhanced the ability to detect these conditions when clinical suspicion is present.² Fluorescein angiography quantifies vascular leakage and helps guide treatment decisions.

Importantly, not all patients with pars planitis require treatment. A comparison of pediatric patients with pars planitis who were treated versus observed found that observed eyes had significantly less anterior chamber and vitreous cell, less vitreous haze, less optic nerve head edema, and lower fluorescein angiography leakage scores than treated eyes; final visual acuity was similar between groups, and no untreated eyes developed complications requiring surgery — supporting selective observation in carefully identified mild cases.¹ Notably, in that same cohort, treated eyes had a substantially higher rate of ocular hypertension (52%) and glaucoma (18.9%) than untreated eyes (0% for both), underscoring that treatment itself carries a meaningful side-effect burden that must be weighed against disease severity.¹ When treatment is indicated, options include periocular or intravitreal corticosteroids, systemic corticosteroids, and steroid-sparing immunomodulatory therapy for chronic or bilateral sight-threatening disease.

Complications

• Cystoid macular edema, the leading cause of vision loss in intermediate uveitis
• Ocular hypertension and steroid-induced glaucoma, a significant risk specifically associated with treatment rather than the disease itself¹
• Cataract, from both chronic inflammation and corticosteroid use
• Vitreous hemorrhage or tractional complications from chronic vitreous inflammation and organization
• Epiretinal membrane formation from chronic low-grade inflammation

Clinical Pearls

• Not all pars planitis requires treatment — carefully selected mild cases without significant leakage or complications can be safely observed¹
• Treatment itself carries substantial risk of ocular hypertension and glaucoma, which must be weighed against the risk of undertreated inflammation¹
• A dilated fundus exam is essential in any patient presenting with new floaters, since intermediate uveitis is easily missed if only the anterior segment is examined²
• PCR and other targeted testing should be used liberally to exclude infectious or neoplastic masquerades before treating as idiopathic pars planitis²
• Fluorescein angiography leakage scores help identify which patients are more likely to need treatment rather than observation¹

Common Pitfalls

• Treating all pars planitis uniformly with immunosuppressive therapy rather than individualizing based on severity and complication risk
• Missing an infectious or neoplastic masquerade by assuming idiopathic pars planitis without adequate exclusionary workup
• Underestimating the side-effect burden (ocular hypertension, glaucoma) of long-term corticosteroid-based treatment
• Failing to perform a dilated fundus exam in a patient presenting with floaters, delaying diagnosis
• Overlooking associated systemic disease (multiple sclerosis, sarcoidosis) that may require its own separate diagnosis and management