13th December 2023

Cornea

A corneal ulcer is a defect of the corneal epithelium and underlying stroma. This is a potentially vision-threatening ocular emergency. Even with prompt treatment, patients can suffer significant morbidity from corneal perforation, scarring, secondary glaucoma and permanent vision loss.

Aetiology:

• Infectious
  • Bacterial infection (most common). Organisms include Staphylococcus species (eyelids) and Pseudomonas aeruginosa (contact lens users).
  • Viral: Herpes viruses are a common cause of viral keratitis. There may be a history of previous herpetic keratitis, recent cold sore (herpes simplex), or recent/concurrent shingles (herpes zoster) affecting the ophthalmic branch (V1) of the trigeminal nerve.
  • Parasitic: Acanthamoeba is a free-living protozoan found in freshwater and soil that can cause corneal ulcers in contact lens wearers. It characteristically causes pain out of proportion to clinical signs due to infiltration of corneal nerves. For this reason, it is often missed in the early stages.
  • Fungal: Less than 10% of all corneal infections. They are most often precipitated by corneal trauma or exposure to organic matter.
• Non-infectious
  • Exposure keratopathy: incomplete eyelid closure (facial nerve palsy; stroke) results in exposure of the inferior third of the cornea, with drying of the tear film and subsequent corneal surface breakdown.
  • Neurotrophic cornea: Corneal sensation is supplied by the trigeminal branch (V1) of the trigeminal nerve. Loss of sensation is a high-risk factor for corneal breakdown. Causes may be local (prolonged contact lens use; herpes virus), systemic neuropathy (diabetes; amyloidosis) or lesion anywhere along the path of V1.
  • Autoimmune: vasculitic corneal ulcers often affect the peripheral cornea and cause rapid and circumferential corneal changes.

Risk Factors

• Contact lens wear
• Severe dry eyes
• Trauma/abrasion
• Nutritional deficiency (malabsorption, liver cirrhosis, alcohol excess)
• Systemic collagen vascular disease
• Corneal exposure secondary to incomplete lid closure (facial nerve palsy)
• Loss of corneal sensation

Clinical Presentation

Slit-lamp examination demonstrates an epithelial defect with an underlying yellow/grey infiltrate. A dendritic appearance is characteristic for herpes simplex keratitis. The presence of a hypopyon (white fluid level within the anterior chamber) indicates sight-threatening disease.

Management

All patients presenting with a red eye and a history of contact lens use should be discussed with the local ophthalmic team. Active corneal ulcers require a corneal scrape for gram staining, microbial culture and sensitivity, viral and acanthamoeba PCR to determine underlying aetiology. Definitive management is directed against the underlying cause.

Image Source: Wikimedia Commons (2015). Parasite140120-fig1 Acanthamoeba keratitis, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Parasite140120-fig1_Acanthamoeba_keratitis.png (Accessed on: 15  May 2022).

Image Source: Wikimedia Commons (2017). Dendritic corneal ulcer, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Dendritic_corneal_ulcer.jpg (Accessed on: 15  May 2022).

Image Source: Wikimedia Commons (2017). Hypopyon 1, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Hypopyon_1.jpg (Accessed on: 15  May 2022).