What is the most likely diagnosis for a patient presenting with gradual blurring of vision, fine stellate keratic precipitates, aqueous flare, and a complicated posterior subcapsular cataract without posterior synechiae?

Fuchs' Heterochromic Iridocyclitis

The most likely diagnosis is Fuchs' heterochromic iridocyclitis (FHI), a chronic, typically unilateral anterior uveitis characterized by fine stellate keratic precipitates, aqueous flare, posterior subcapsular cataract, and notably the absence of posterior synechiae. 1

Key Diagnostic Features Present

The clinical presentation demonstrates the classic triad of FHI:

• Fine stellate keratic precipitates are present in 80-100% of FHI cases and represent a pathognomonic finding 1, 2
• Aqueous flare indicating chronic low-grade inflammation occurs in approximately 60% of cases 1
• Complicated posterior subcapsular cataract develops in 69-82% of affected eyes due to chronic iridocyclitis 1, 3, 2

Critical Distinguishing Feature

The absence of posterior synechiae is a defining characteristic of FHI, occurring in 100% of cases, which differentiates it from other forms of chronic anterior uveitis. 1 This finding is particularly important because most other chronic anterior uveitides (such as juvenile idiopathic arthritis-associated uveitis) commonly develop posterior synechiae as a complication of inflammation 4.

Additional Clinical Context

Expected Associated Findings

• Iris heterochromia may or may not be clinically evident, particularly in dark-eyed patients where it is present in only 25% of cases 2
• Iris stromal atrophy is universally present (100%) even when heterochromia is not clinically apparent 1
• Vitreous opacities occur in 84% of cases 1
• Unilateral presentation in approximately 90% of patients 1, 2

Symptom Pattern

• Gradual blurring of vision is the most common presenting symptom (42.3% of cases) 3
• Absence of acute symptoms such as severe redness, pain, or photophobia occurs in 100% of cases, distinguishing FHI from acute anterior uveitis 1

Important Complications to Monitor

Glaucoma Risk

• Secondary glaucoma develops in 14.8-30.66% of affected eyes and represents a major threat to vision 3, 2
• Elevated intraocular pressure should be monitored regularly, as it may develop insidiously 1, 3

Cataract Management

• Cataract extraction is eventually required in approximately 40.7% of cases 3
• Pre- and postoperative anti-inflammatory treatment should be performed to minimize inflammation risk, though FHI patients typically tolerate surgery well without severe postoperative uveitis 3
• Visual outcomes after cataract surgery may be limited by posterior capsule opacification, glaucoma, and persistent vitreous opacity 3

Potential Etiologic Associations

Recent evidence suggests possible infectious triggers:

• Toxoplasma gondii has been implicated, with FHI potentially developing 2-13 years after ocular toxoplasmosis as a post-infectious immune reaction 5
• Rubella virus has shown intraocular antibody production in some FHI cases 6
• These associations suggest FHI may represent a secondary immune reaction to past antigenic stimulation rather than active infection 5

Management Approach

Most patients (73%) do not require active anti-inflammatory treatment because the inflammation is typically mild and chronic 3. This contrasts sharply with other forms of chronic anterior uveitis (such as JIA-associated uveitis) that require aggressive topical glucocorticoid therapy to prevent complications like posterior synechiae 4.

The primary management focuses on:

• Monitoring for glaucoma development 3, 2
• Timely cataract extraction when visually significant 3
• Avoiding unnecessary immunosuppressive therapy that would be indicated for other uveitis entities 3