What is the difference between hypopyon and keratitis?

Difference Between Hypopyon and Keratitis

Keratitis is an inflammation of the cornea, while hypopyon is a collection of white blood cells in the anterior chamber that can occur as a complication of severe keratitis or other inflammatory conditions. 1

Keratitis

Definition and Characteristics

• Inflammation of the cornea that can be infectious or non-infectious
• Typically presents with:
  • Corneal epithelial defects
  • Stromal infiltrates (white cell infiltration in surrounding stroma)
  • Corneal edema
  • Ulceration (particularly with bacterial keratitis)
  • Indistinct edges around infiltrates (especially in bacterial keratitis) 1

Clinical Features

• Pain, redness, discharge, blurred vision, photophobia
• Epithelial defects visible with fluorescein staining
• Stromal infiltrates that may vary in:
  • Location (central, peripheral, inferior, perineural)
  • Density, size, shape (ring-shaped, satellite lesions)
  • Depth and character of margins (suppuration, necrosis, feathery) 1

Types

1. Bacterial keratitis: Often presents with suppurative stromal infiltrates >1mm with indistinct edges
2. Viral keratitis: May present with dendritic patterns (HSV) or pseudodendritic patterns (VZV)
3. Fungal keratitis: Often presents with feathery borders, satellite lesions
4. Acanthamoeba keratitis: Often presents with ring infiltrates

Hypopyon

Definition and Characteristics

• Collection of white blood cells that settles in the inferior anterior chamber
• Appears as a white or yellowish fluid level in the anterior chamber
• Usually sterile in bacterial keratitis (does not contain viable organisms) 1
• May present as blunting of the inferior angle or at 3:00 or 9:00 if the patient was recently lying down 1

Clinical Significance

• Indicates severe intraocular inflammation 2
• Associated with:
  • Severe bacterial or fungal keratitis
  • Endophthalmitis
  • Certain inflammatory conditions
  • Occasionally neoplastic conditions 2

Important Distinctions

• Hypopyon is a sign/complication, not a disease itself
• It occurs in approximately 52.6% of fungal keratitis cases 3
• Can cause ocular hypertension (88.7% of eyes with ocular hypertension in fungal keratitis had hypopyon) 3
• Presence of hypopyon increases likelihood of requiring surgical intervention 3

Key Differences

1. Anatomical location:

   • Keratitis: Occurs in the cornea
   • Hypopyon: Occurs in the anterior chamber

2. Pathophysiology:

   • Keratitis: Primary inflammatory or infectious process in corneal tissue
   • Hypopyon: Secondary accumulation of inflammatory cells in response to severe infection or inflammation

3. Diagnostic significance:

   • Keratitis: Indicates primary corneal disease
   • Hypopyon: Indicates severity of inflammation, often a complication of keratitis

4. Management implications:

   • The presence of hypopyon in keratitis suggests a more severe infection requiring more aggressive treatment
   • Hypopyon in bacterial keratitis is usually sterile and does not require direct sampling unless endophthalmitis is suspected 1

Clinical Pearls and Pitfalls

• Hypopyon with retrocorneal plaques can occur in viral keratitis and may mimic fungal or bacterial keratitis, potentially leading to misdiagnosis 4
• In fungal keratitis, hypopyon may have a pyramidal shape and is often associated with prominent geographical corneal infiltration and satellite lesions 5
• Risk factors for developing hypopyon in fungal keratitis include long duration of symptoms, large lesion size, and infections caused by Fusarium and Aspergillus species 3
• Approximately 47% of hypopyon samples in fungal keratitis are culture-positive for fungi 3
• Rare manifestations can include intracorneal hypopyon, where the inflammatory cells accumulate within the corneal stroma rather than the anterior chamber 6

Management Considerations

• The presence of hypopyon generally indicates a need for more aggressive treatment
• Aqueous or vitreous taps should not be performed on hypopyon unless there is high suspicion of endophthalmitis (e.g., following intraocular surgery, perforating trauma, or sepsis) 1
• Resolution of hypopyon is one of the clinical features suggesting a positive response to antibiotic therapy 1