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Herpes Simplex Virus (HSV) Keratitis

URGENT — Cornea

Symptoms

red eye, pain, and foreign body sensation

photophobia and tearing

decreased vision

vesicular skin rash (e.g., eyelids)

usually unilateral; history of previous episodes

Clinical Findings

Epithelial keratitis (active viral replication)

  • dendritic keratitis: thin, linear, branching ulcer with pathognomonic club-shaped terminal bulbs
  • geographic ulcer: large, amoeba-shaped ulcer with dendritic edges (often driven by topical steroids)
  • staining: central ulceration stains with fluorescein; swollen borders stain with rose bengal/lissamine green
  • hallmark: significantly decreased corneal sensation

Eyelid & conjunctival involvement

  • clear vesicles on an erythematous base progressing to crusting
  • acute unilateral follicular conjunctivitis ± conjunctival dendrites

Stromal & endothelial disease (immune-mediated)

  • disciform endotheliitis: central disc of stromal/epithelial edema with underlying kps
  • necrotizing stromal keratitis: opaque, necrotic infiltrate with high risk of thinning/perforation
  • "ghost dendrites": subepithelial scars remaining after epithelial resolution

Neonatal/pediatric HSV

  • rare but devastating; often bilateral with severe cns or multiorgan involvement
  • increased risk of extensive scarring and astigmatism

Etiology

Pathogenesis

  • primary hsv-1 infection typically occurs in childhood; virus establishes latency in trigeminal ganglion
  • reactivation triggers: uv light, fever, stress, immunosuppression, menstruation, or trauma

Mechanism

  • epithelial disease reflects live viral replication
  • stromal and endothelial disease are largely immune-mediated responses to viral antigens

Red Flags

central stromal thinning or impending perforation

hsv endotheliitis with corneal edema and significant iop elevation

concurrent iritis with hypopyon

atypical dendrites in a contact lens wearer (rule out acanthamoeba)

Investigations

Clinical exam

  • test corneal sensation with a cotton wisp before instilling anesthetic
  • slit-lamp evaluation with fluorescein and rose bengal/lissamine green
  • dilated fundus exam to rule out viral retinitis

Laboratory (if diagnosis is unclear)

  • viral pcr or culture: swab cornea, conjunctiva, or unroofed skin vesicles
  • giemsa stain: shows multinucleated giant cells
  • hsv antibody titers: absence of hsv-1 antibodies helps rule out hsv stromal disease

Treatment

Epithelial disease

  • oral: acyclovir 400 mg 5x/day or valacyclovir 500 mg t.i.d. for 7–10 days (preferred by many)
  • topical: ganciclovir 0.15% gel 5x/day until healed, then t.i.d. for 7 days
  • adjunct: limited debridement of infected epithelial cells

Stromal/endothelial disease

  • topical steroids (e.g., prednisolone acetate 1%) with prophylactic antiviral cover

Adjunctive therapy

  • cycloplegic (cyclopentolate 1% t.i.d.) for photophobia/ac reaction
  • prophylactic topical antibiotic to prevent secondary infection
  • long-term oral prophylaxis (acyclovir 400 mg b.i.d.) to reduce recurrence risk

Clinical Pearl

HSV keratitis is the most common cause of corneal blindness in developed countries. Reduced corneal sensation is a key clinical clue — test with a wisp of cotton before touching the cornea. Dendritic ulcers have pathognomonic terminal bulbs; pseudodendrites (e.g., healing abrasion, acanthamoeba) lack these bulbs.

Differential Diagnosis

  • herpes zoster ophthalmicus (pseudodendrites lack terminal bulbs)
  • acanthamoeba keratitis
  • healing corneal abrasion
  • toxic keratopathy (medicamentosa)

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