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Keratitis

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Overview

Keratitis describes the inflammation of the cornea and is an ophthalmic emergency as it can be sight-threatening. It is usually due to infection. Non-infectious causes of keratitis are rare.

Trauma, foreign bodies, and contact lenses can enable the entry of infectious pathogens into the cornea.

Causes

Infectious causes

Bacterial causes:

  • Pseudomonas aeruginosa – more common in contact lens wearers
  • Staphylococcus aureus
  • Streptococcus pneumoniae
  • Haemophilus influenzae

Fungal causes:

  • Aspergillus species
  • Candida albicans

Viral causes:

  • Herpes simplex
  • Varicella zoster
  • Cytomegalovirus – rare
  • Epstein-Barr virus – rare

Protozoal causes:

  • Acanthamoeba species – increased risk in contact lens wearers
    • Usually, cause extreme pain out of proportion to clinical findings
    • Usually found in soil and contaminated water and it survives boiling, freezing, and chlorination of swimming pools

Non-infectious causes

Epidemiology

  • Pseudomonas aeruginosa is more commonly seen in contact lens wearers
  • Acanthamoeba species are more commonly seen in contact lens wearers

Risk Factors

  • Eye trauma, particularly to the cornea
  • Contact lens wearers
  • Immunocompromised patients
  • Autoimmune disease presence

Presentation

Patients usually have a painful, erythematous, and gritty eye. Features may be:

  • Pain in the eye
    • If the pain is disproportionate to clinical findings, suspect Acanthamoeba species
  • Red eye
  • Grittiness – patients often feel like something is stuck in their eye
  • Photophobia 
  • Hypopyon may be seen
  • Corneal infiltrates may be seen:
    • This is opacification of the cornea due to pathogens and inflammatory cells
  • Corneal ulcers may be present – infiltrates with an overlying epithelial defect
  • Branching lesions suggest a herpetic infection

Investigations

Overview

  • Immediate (within 24 hours) ophthalmology referral:
    • Any contact lens wearer that has an acute painful red eye should have an immediate referral to ophthalmology
    • This is because an accurate diagnosis can only be made using a slit-lamp examination 
  • Slit-lamp examination – diagnostic test:
    • May show hypopyon, corneal infiltrates, ulcers etc.
    • Herpes simplex keratitis may have a dendritic (branching) corneal ulcer
    • Fluorescein staining may make the ulcer glow green/blue under cobalt blue light
  • Intraocular pressure measurement:
    • To rule out glaucoma which may arise as a complication
  • Corneal scrapings and gram stain, microscopy, cultures, and sensitivity:
    • May show causative organism

Other investigations

  • Other investigations to consider are:
    • FBC:
      • Usually normal but derangements can suggest immunodeficiency or systemic infection
  • HIV testing:
    • If unusual infections are present such as Microsporidia

Management

  • Stop wearing contact lenses until keratitis has fully resolved
  • 1st-line: antibiotic eyedrops – usually fluoroquinolones (e.g. moxifloxacin)
  • If photophobia present: atropine or cyclopentolate eye drops
    • These paralyse the ciliary muscles and dilate the eye, providing pain relief

Patient Advice

  • Patients should stop wearing contact lenses until the keratitis has completely resolved
  • Patients should avoid wearing contact lenses overnight
  • For pregnant people, antenatal screening for Herpes simplex and gonococcal infections can be used to prevent neonatal keratitis
  • For patients who have had herpetic keratitis, they should be informed that the disease may become recurrent
  • All patients should be safety-netted on the recurrence of symptoms and seek help if symptoms recur

Complications

  • Corneal scarring
  • Glaucoma
  • Cataracts – can be treated with keratoplasty
  • Corneal perforation
  • Endophthalmitis – spread of the infection into the intraocular cavities

Prognosis

  • Patients that are treated promptly have a good prognosis and can retain good vision
  • Some patients with herpetic keratitis can have a recurrence of symptoms

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