Intermediate Uveitis / Pars Planitis

Anatomic Definition

Intermediate uveitis is defined by the SUN (Standardization of Uveitis Nomenclature) Working Group as inflammation whose primary anatomic site is the vitreous and pars plana, distinguishing it from anterior uveitis (chamber-centered) and posterior uveitis (choroid/retina-centered). As with every category in the SUN system, what matters is where the disease is centered — a case with predominant vitreous inflammation is intermediate uveitis even if trace anterior chamber cell is also present, just as anterior uveitis with a little vitreous spillover doesn't become intermediate uveitis on that basis alone.

Pars planitis is the specific term for idiopathic intermediate uveitis — cases with the same vitreous/pars-plana-centered inflammation but no identifiable infectious or systemic cause, and it's the subtype that most consistently produces the two exam findings described below.

Snowballs and Snowbanking

The two signature findings of intermediate uveitis both reflect where gravity and the ocular anatomy send inflammatory debris. Vitreous snowballs are aggregates of inflammatory cells — often composed of macrophages and other leukocytes — that accumulate in the inferior vitreous cavity, settling there simply because that's the dependent portion of the eye. Snowbanking is a more severe and more specific finding: exudative, white fibrovascular material that coats the inferior pars plana and ora serrata, representing organized exudate and fibrovascular tissue rather than loose cellular debris. Snowbanking is a hallmark of pars planitis in particular, and it carries its own risk — the fibrovascular tissue it's made of can develop neovascularization, which in turn can bleed into the vitreous cavity.

Clinical Course and Complications

Intermediate uveitis is frequently bilateral, and because the inflammation is centered in the vitreous rather than the more symptomatic anterior chamber, it tends to present with floaters and gradually blurred vision rather than the pain, photophobia, and redness typical of acute anterior uveitis — patients can have significant disease with a comparatively quiet, white eye.

The complication that drives most treatment decisions is cystoid macular edema (CME): fluid accumulation in the macula secondary to chronic vitreous inflammation and vascular leakage, which is the leading cause of vision loss in intermediate uveitis. Monitoring for CME — clinically and with macular imaging — is therefore a central part of managing any patient with this diagnosis, independent of how mild the vitreous cell count itself might look.

Although pars planitis is idiopathic by definition, a meaningful minority of patients are later found to have an associated systemic condition, most notably multiple sclerosis — a reason ongoing intermediate uveitis, especially when bilateral, is often paired with at least a baseline neurologic history and low threshold for referral if other MS-suggestive symptoms appear.

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