Corneal Tuberculosis

Corneal tuberculosis is a rare but serious extrapulmonary manifestation of Mycobacterium tuberculosis infection affecting the anterior segment of the eye. It can occur either as a primary infection or secondary to systemic tuberculosis.

Key Points:

• Incidence: Represents < 1% of all ocular TB cases
• Age Group: Most common in children and young adults
• Risk Factors: Malnutrition, immunosuppression, close contact with TB patients
• Transmission: Direct inoculation or hematogenous spread

Pathophysiology

Mechanisms of Infection:

• Direct corneal invasion by M. tuberculosis
• Hematogenous spread from primary focus
• Contiguous spread from adjacent structures

Immunological Response:

• Cell-mediated immunity plays crucial role
• Formation of granulomas
• Release of inflammatory mediators
• Corneal neovascularization

Clinical Features

Common Presentations:

• Interstitial keratitis
• Phlyctenular keratoconjunctivitis
• Peripheral ulcerative keratitis
• Disciform keratitis

Symptoms:

• Decreased vision
• Photophobia
• Foreign body sensation
• Redness and pain
• Excessive tearing

Signs:

• Corneal infiltrates
• Stromal inflammation
• Corneal vascularization
• Anterior chamber reaction

Diagnosis

Clinical Evaluation:

• Detailed history including TB exposure
• Slit lamp examination
• Visual acuity assessment
• Corneal sensation testing

Laboratory Tests:

• Mantoux test (TST)
• Interferon-γ release assays (IGRAs)
• Chest X-ray
• PCR of corneal scraping
• Corneal biopsy (if required)

Treatment

Anti-tubercular Therapy (ATT):

• Initial Phase (2 months):
  • Isoniazid (H)
  • Rifampicin (R)
  • Pyrazinamide (Z)
  • Ethambutol (E)
• Continuation Phase (4-7 months):
  • Isoniazid
  • Rifampicin

Supportive Treatment:

• Topical steroids
• Cycloplegics
• Lubricating eye drops
• Regular monitoring of liver function

Complications

Early Complications:

• Corneal scarring
• Anterior synechiae
• Secondary glaucoma
• Anterior segment inflammation

Late Complications:

• Permanent vision loss
• Corneal opacity
• Irregular astigmatism
• Corneal perforation