Harvey's Garden

Keratitis

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aliasesHerpes zoster keratitis, Bacterial keratitis, Herpes simplex keratitis

4 min read

Epidemiology & Risk Factors

  • Contact Lens (CL) Wear: Most common risk factor for infectious keratitis; extended-wear CLs confer the highest risk (Pseudomonas aeruginosa).
  • Freshwater/Tap Water Exposure: Swimming or cleaning CLs with tap water increases risk for Acanthamoeba.
  • Ocular Trauma: Vegetative/agricultural matter trauma predisposes to fungal keratitis (Fusarium, Aspergillus, Candida).
  • Immunosuppression & Topical Glucocorticoid Use: Increases susceptibility to fungal and viral keratitis (HSV, VZV).
  • Ocular Surface Impairment: Dry eye syndrome, lagophthalmos (e.g., CN VII palsy → exposure keratitis), prior corneal surgery.
  • UV Light Exposure: Welder’s arc, tanning beds, or snow reflection without eye protection (photokeratitis).

Clinical Features

  • History:
    • Rapid onset of severe ocular pain, foreign body sensation, photophobia, excessive tearing, and decreased visual acuity.
    • Acanthamoeba: Severe pain out of proportion to exam findings.
    • Photokeratitis: Bilateral eye pain and photophobia with a 6–12 hour latency after UV exposure.
  • Physical Examination:
    • Ciliary flush (circumcorneal injection).
    • Corneal infiltrate/opacity: Focal, round, white/gray stromal spot visible with penlight or slit-lamp.
    • Hypopyon: Layering of WBCs in the anterior chamber (indicates severe inflammation/bacterial keratitis).
    • Fluorescein Staining Findings:
      • Bacterial/Fungal: Focal epithelial defect overlying a dense stromal infiltrate.
      • Herpes Simplex Virus (HSV): Dendritic branching ulcer with terminal bulbs.
      • Herpes Zoster Ophthalmicus (VZV): Pseudodendrites (raised mucous plaques without terminal bulbs); associated with Hutchinson sign (vesicles at the tip of the nose, CN distribution).
      • Photokeratitis: Diffuse, bilateral punctate corneal epithelial defects.

Diagnosis

  • Initial / Screening:
    • Slit-lamp examination: Evaluates depth of corneal involvement, anterior chamber reaction (cells/flare, hypopyon), and corneal thinning.
    • Fluorescein stain with cobalt blue light: Demonstrates characteristic epithelial breakdown (e.g., dendritic ulcers, punctate lesions).
  • Confirmatory / Gold Standard:
    • Corneal scraping for Gram stain, Giemsa stain, and culture:
      • Indicated for large, central, or vision-threatening stromal infiltrates before initiating Abx.
      • Media includes blood, chocolate, and Sabouraud agar; non-nutrient agar with an E. coli overlay is utilized for suspected Acanthamoeba.
    • PCR: High sensitivity/specificity for HSV and VZV DNA from corneal swabs or scrapings.

Differential Diagnostics

  • Bacterial Conjunctivitis:
    • Diff: Visual acuity is normal, cornea is clear without infiltrate, no ciliary flush (diffuse conjunctival injection), and no fluorescein uptake on the cornea.
  • Acute Angle-Closure Glaucoma (AACG):
    • Diff: Mid-dilated and non-reactive pupil, shallow anterior chamber, markedly elevated IOP (> 30–40 mmHg), “steamy/hazy” cornea without a focal ulcer or fluorescein staining, systemic signs (headache, nausea/vomiting).
  • Anterior Uveitis (Iritis):
    • Diff: Constricted or sluggish pupil, leukocytes/flare in the anterior chamber, ciliary flush, but no corneal epithelial defect on fluorescein stain.
  • Corneal Abrasion:
    • Diff: Direct mechanical trauma history; fluorescein reveals an epithelial defect (often linear) without an underlying white stromal opacity/infiltrate or hypopyon.
  • Scleritis:
    • Diff: Deep, boring ocular pain radiating to the temple/face, violaceous scleral hue, vessels that do not blanch with topical phenylephrine; cornea is classically unaffected initially.

Management

  1. Immediate General Measures:
    • Emergency Ophthalmology consult (sight-threatening condition).
    • Discontinue CL wear immediately; save CL and lens case for culture.
    • Absolute Contraindication: Topical corticosteroids without specialist guidance (exacerbates fungal/viral replication, accelerates corneal melting and perforation).
  2. Etiology-Directed Pharmacotherapy:
    • Bacterial Keratitis:
      • First-line: Topical broad-spectrum fluoroquinolones (e.g., moxifloxacin, ofloxacin, or ciprofloxacin drops).
      • Severe / Central / Refractory: Fortified alternating topical antibiotics (e.g., topical vancomycin + topical tobramycin or cefazolin).
    • Viral Keratitis:
      • HSV: Topical ganciclovir (0.15% gel) or oral acyclovir / valacyclovir.
      • VZV (HZO): High-dose oral acyclovir (800 mg 5x/day) or oral valacyclovir (1000 mg TID) initiated within 72 hours of rash onset.
    • Fungal Keratitis:
      • First-line: Topical natamycin (5%) for filamentous fungi (Fusarium, Aspergillus); topical amphotericin B (0.15%) for yeast (Candida).
      • Second-line / Deep stromal: Topical and/or systemic voriconazole.
    • Acanthamoeba Keratitis:
      • First-line: Topical biguanides (polyhexamethylene biguanide [PHMB] 0.02%) or chlorhexidine (0.02%) combined with a diamidine (propamidine).
    • Photokeratitis:
      • Supportive: Topical antibiotic ointment (erythromycin), oral NSAIDs for analgesia; typically resolves spontaneously within 24–72 hours.
  3. Refractory / Surgical Management:
    • Therapeutic Penetrating Keratoplasty (Corneal Transplant): Indicated for medically refractory infection, impending corneal perforation, or severe visual loss from dense corneal scarring.

Complications

  • Corneal Ulceration & Perforation: Progressive stromal necrosis causing loss of globe integrity.
  • Corneal Scarring & Astigmatism: Resulting in irreversible loss of visual acuity.
  • Endophthalmitis: Intraocular extension of infection requiring urgent intravitreal antibiotics and vitrectomy.
  • Secondary Glaucoma: Due to trabecular meshwork clogging by inflammatory debris or peripheral anterior synechiae formation.
  • Permanent Blindness.

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