Keratitis, Corneal Ulcers, and Corneal Abrasions

1. KERATITIS

A. Bacterial Keratitis

Etiology

• Pseudomonas aeruginosa - Gram-negative bacillus; responsible for >60% of contact lens-related keratitis. Typically aggressive.
• Staphylococcus aureus - Gram-positive, coagulase-positive; tends to present as a focal, fairly well-defined white or yellow-white infiltrate.
• Streptococci (S. pyogenes, S. pneumoniae) - Often run an aggressive course.

• Contact lens wear - the most important risk factor, especially extended-wear soft lenses. Even daily disposables and apparently meticulous hygiene are not fully protective.
• Trauma (including refractive surgery, particularly LASIK)
• Agricultural injury (especially in developing countries, where fungal co-infection should be considered)
• Ocular surface disease: herpetic keratitis, bullous keratopathy, dry eye, chronic blepharitis, trachoma/entropion, exposure keratopathy, severe allergy, corneal anaesthesia
• Systemic: immunosuppression, diabetes, vitamin A deficiency

Clinical Features

• Symptoms: Unilateral pain, photophobia, blurred vision, mucopurulent or purulent discharge
• Signs:
  • Epithelial defect with infiltrate involving a larger area + significant circumcorneal (ciliary) injection
  • Stromal oedema, Descemet membrane folds
  • Anterior uveitis, commonly with a hypopyon and posterior synechiae in moderate-to-severe cases
  • Plaque-like keratic precipitates on the endothelium contiguous with affected stroma
  • Chemosis and eyelid swelling in severe cases
  • Severe ulceration may lead to descemetocoele formation and perforation (especially in Pseudomonas and Staphylococcus infections)

"Bacterial corneal ulceration should be excluded in a patient who wears contact lenses and presents with a painful red eye and blurred vision." - Kanski's Clinical Ophthalmology, 10th ed.

B. Fungal Keratitis

Etiology

• Yeasts (e.g., Candida spp.) - responsible for most cases in temperate climates; typical in immunocompromised patients.
• Filamentous fungi (e.g., Fusarium, Aspergillus) - the dominant pathogens in tropical climates; frequently follow agricultural trauma involving plant matter or gardening tools.

Clinical Features

• Symptoms have a gradual onset: pain, grittiness, photophobia, blurred vision, watery or mucopurulent discharge.
• Diagnosis is frequently delayed because fungal infection mimics bacterial disease.
• Candida keratitis: yellow-white densely suppurative infiltrate.
• Filamentous keratitis:
  • Grey or yellow-white stromal infiltrate with indistinct, fluffy margins
  • Progressive infiltration, often with satellite lesions or a ring-shaped infiltrate
  • Endothelial plaque and hypopyon may develop
• Corneal perforation is common and prognosis for vision is frequently poor.

C. Herpes Simplex Keratitis (HSK)

Etiology

Clinical Features - Epithelial Keratitis (active viral replication)

• Dendritic ulcer: a branching, linear corneal ulcer with characteristic terminal bulbs at the ends; stains with fluorescein at the base and rose bengal at the edges. This is the hallmark of active HSV.
• Geographic ulcer: a large irregular "map-shaped" epithelial ulcer representing coalescence of multiple dendrites, often triggered by inappropriate topical steroid use.
• Symptoms: unilateral eye pain, photophobia, reduced visual acuity, tearing, foreign body sensation.
• Corneal sensation is characteristically reduced or absent (due to viral neurotrophic damage).

Clinical Features - Stromal Keratitis (immune-mediated)

• Disc-shaped (disciform) stromal oedema with overlying Descemet folds
• Mild anterior uveitis; raised IOP may occur
• No epithelial ulceration in immune stromal keratitis
• Recurrence rate: ~10% at 1 year, ~50% at 10 years after first episode

D. Acanthamoeba Keratitis

Etiology

Clinical Features

• Severe, disproportionate pain - often out of proportion to the clinical signs (a hallmark feature).
• Ring-shaped stromal infiltrate is characteristic (though not universal).
• Radial keratoneuritis - infiltration along corneal nerves - is a highly specific early sign.
• Slowly progressive course; initially often misdiagnosed as HSV keratitis.
• Hypopyon and scleritis may develop.

E. Herpes Zoster (VZV) Keratitis

Etiology/Clinical Features

• Results from reactivation of varicella-zoster virus in the trigeminal ganglion (ophthalmic division = herpes zoster ophthalmicus).
• Can cause epithelial keratitis (pseudodendrite - a poorly staining mucous plaque, without true epithelial erosion, unlike HSV), stromal keratitis, uveitis, scleritis, and elevated IOP.
• Hutchinson's sign (rash on the tip of the nose) predicts ocular involvement.
• Anterior chamber shows cells and flare; consider immunocompromise if patient is <40 years old.

2. CORNEAL ULCER

Etiology

• Desquamation (e.g., exposure keratitis from Bell's palsy causing corneal desiccation and sloughing)
• Trauma (direct inoculation of organisms)
• Direct microbial invasion (e.g., N. gonorrhoeae)

Clinical Features

• History: contact lens use, prior ocular surgery or injury, recent trauma, history of genital herpes, topical or systemic steroids
• Symptoms:
  • Eye redness and lid/conjunctival swelling
  • Ocular pain or foreign body sensation
  • Photophobia
  • Mucopurulent or purulent discharge
  • Blurred vision (especially if the ulcer is in the central visual axis or if uveal tract inflammation is present)
• Signs on slit lamp:
  • Epithelial defect with underlying stromal opacity/infiltrate
  • Hypopyon (sterile pus in the anterior chamber) in severe cases
  • Descemetocoele (herniation of Descemet membrane) with risk of perforation
  • Fluorescein staining confirms the epithelial defect
  • Reduced or absent corneal sensation in herpetic or neurotrophic ulcers

"A corneal ulcer is a serious infection involving multiple layers of the cornea and develops secondary to breaks in the epithelial barrier, so that infectious agents invade the underlying corneal stroma." - Tintinalli's Emergency Medicine, 9th ed.

3. CORNEAL ABRASION

Etiology

• Contact lens wear (most common)
• Fingernails, makeup brushes
• Foreign objects blown into the eye (wind, outdoor work)
• Overhead work (mechanics, construction workers - objects falling into the eye)
• High-speed machinery (grinders, lawn mowers, weed whackers, hammering metal) - important to note these carry risk of corneal laceration and globe perforation

Clinical Features

• Intense eye pain - may be delayed several hours after the inciting event
• Foreign body sensation
• Photophobia
• Tearing/lacrimation
• Decreased visual acuity if the abrasion is in the central visual axis or if iritis develops

• Conjunctival injection
• Tearing and lid swelling
• Blepharospasm (severe pain causing involuntary lid closure; may require topical anaesthetic to complete examination)
• The abrasion may be visible to the naked eye as an irregular area of light reflection off the cornea
• Relief of pain with topical anaesthesia is virtually diagnostic of corneal abrasion

• Superficial, irregular corneal defect appearing bright green under cobalt blue light after fluorescein instillation
• No corneal infiltrate (distinguishes it from keratitis/ulcer)
• Multiple fine vertical linear abrasions suggest a foreign body embedded in the tarsal conjunctiva of the upper lid (evert the lid to check)
• In large abrasions >24 hours old: flare and cells from iritis may appear, but still no stromal infiltrate
• Seidel test negative (no aqueous leak = no perforation)

Summary Comparison