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Peripheral Ulcerative Keratitis

Cornea

1. Peripheral Ulcerative Keratitis

CLINICAL ANALOGY - THE BORDER PATROL GONE ROGUE

The Master Analogy: Imagine the peripheral cornea as a fortified border zone - highly vascular, immunologically active, and under constant surveillance. In PUK, your own immune system's "border patrol" (neutrophils, MMPs, autoantibodies) turns against the host tissue instead of protecting it. The limbal vasculature becomes the staging ground for a self-destructive inflammatory assault that eats through stroma like acid - crescent-shaped, remorseless, and potentially blinding. Unlike central ulcers caused by pathogens, PUK is fundamentally a collagen dissolution disease driven by systemic vasculitis masquerading as an eye problem.
Key Conceptual Insight: PUK that is "idiopathic" is a diagnosis of exclusion - in ~50% of cases with active systemic vasculitis, a fatal vasculitic process (e.g., Wegener's GPA, RA) is concurrently underway. The cornea becomes your diagnostic window to systemic disease.

Peripheral Ulcerative Keratitis (PUK) is defined as a crescent-shaped inflammatory ulceration of the peripheral corneal stroma within 2 mm of the limbus, associated with an epithelial defect and progressive stromal dissolution - may occur in association with local ocular or systemic inflammatory disease, but infectious, postsurgical/traumatic, and idiopathic causes also occur.
Peripheral Ulcerative Keratitis (PUK) is not exclusively non-infectious; infectious disease is a recognized etiologic category, while microbial superinfection may complicate non-infectious disease.

Parameter	Details
Incidence	• Rare • Estimated incidence: 0.2–3 cases per million people per year • Exact epidemiological figures are scarce
Age of peak onset	• Predominantly affects middle-aged to older adults • Exact peak age varies between cohorts • A specific correspondence with the peak age of systemic autoimmune diseases is not established
Sex predilection	• Sex distribution varies between cohorts • Female predominance may reflect associated autoimmune disease • Male predominance or near-equal distribution is also reported • Granulomatosis with polyangiitis (GPA) is more common in men
Laterality	• Usually unilateral • Bilateral involvement is associated with systemic autoimmune disease
Systemic association	• Approximately half of cases are related to systemic collagen vascular disease • Rheumatoid arthritis (RA) is the most common systemic association • Granulomatosis with polyangiitis (GPA) is another major systemic association
Mortality risk	• Historical cohort: 9 of 17 patients receiving conventional therapy died from a vascular-related event during 10 years • Long-term immunosuppression group: 1 of 17 patients died during 10-year follow-up • Peripheral ulcerative keratitis and necrotizing scleritis may signal potentially lethal systemic vasculitis in rheumatoid arthritis

Parameter	Details
Incidence	• Rare • Estimated incidence: 0.2–3 cases per million people per year • Exact epidemiological figures are scarce
Age of peak onset	• Predominantly affects middle-aged to older adults • Exact peak age varies between cohorts • A specific correspondence with the peak age of systemic autoimmune diseases is not established
Sex predilection	• Sex distribution varies between cohorts • Female predominance may reflect associated autoimmune disease • Male predominance or near-equal distribution is also reported • Granulomatosis with polyangiitis (GPA) is more common in men
Laterality	• Usually unilateral • Bilateral involvement is associated with systemic autoimmune disease
Systemic association	• Approximately half of cases are related to systemic collagen vascular disease • Rheumatoid arthritis (RA) is the most common systemic association • Granulomatosis with polyangiitis (GPA) is another major systemic association
Mortality risk	• Historical cohort: 9 of 17 patients receiving conventional therapy died from a vascular-related event during 10 years • Long-term immunosuppression group: 1 of 17 patients died during 10-year follow-up • Peripheral ulcerative keratitis and necrotizing scleritis may signal potentially lethal systemic vasculitis in rheumatoid arthritis

ANATOMICAL CORRELATES - WHY THE PERIPHERY?
The peripheral cornea has distinct anatomical and immunological features that predispose it to immune-mediated inflammation.
Understanding the peripheral distribution of peripheral ulcerative keratitis (PUK) requires knowledge of limbal anatomy:

Anatomical Feature	Immunological Consequence
• Rich limbal vascular arcade	• Provides substrate for immune complex deposition • Allows neutrophil/T-cell trafficking
• High density of Langerhans cells at periphery	• Antigen presentation amplified • Drives local T-cell activation
• Major histocompatibility complex class II-positive antigen-presenting cells at the limbus and peripheral cornea	• Antigen presentation supports local T-cell activation
• Peripheral corneal vascular architecture facilitates immune-complex deposition	• Immune-complex activation of the classical complement pathway recruits inflammatory cells • Inflammatory cytokines promote matrix metalloproteinase release → collagenolysis
• Transition zone: vascular → avascular cornea	• Creates inflammatory "frontier" • Central cornea relatively protected by avascularity
• Palisades of Vogt - limbal stem cell niche	• Destruction → limbal stem cell deficiency • Conjunctivalization of cornea

Anatomical Feature	Immunological Consequence
• Rich limbal vascular arcade	• Provides substrate for immune complex deposition • Allows neutrophil/T-cell trafficking
• High density of Langerhans cells at periphery	• Antigen presentation amplified • Drives local T-cell activation
• Major histocompatibility complex class II-positive antigen-presenting cells at the limbus and peripheral cornea	• Antigen presentation supports local T-cell activation
• Peripheral corneal vascular architecture facilitates immune-complex deposition	• Immune-complex activation of the classical complement pathway recruits inflammatory cells • Inflammatory cytokines promote matrix metalloproteinase release → collagenolysis
• Transition zone: vascular → avascular cornea	• Creates inflammatory "frontier" • Central cornea relatively protected by avascularity
• Palisades of Vogt - limbal stem cell niche	• Destruction → limbal stem cell deficiency • Conjunctivalization of cornea

Exam pearl

Table 2: Limbal anatomical features and their immunopathological significance.

Surgical Anatomy Pearl: The peripheral cornea is thicker (~650–700 µm) than the centre (~520 µm).
However, peripheral ulcerative keratitis (PUK) can progress rapidly because of immune-mediated stromal destruction and may lead to perforation.
Corneal perforation is an ophthalmic emergency and may cause aqueous leakage, a shallow anterior chamber, hypotony, and iris prolapse. It is a full-thickness corneal defect rather than stromal thinning alone.

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