👁️ Herpes Simplex Keratitis (HSK) – MSRA Deep Dive

Definition

• Herpes Simplex Keratitis (HSK) is viral inflammation and ulceration of the cornea caused mostly by herpes simplex virus type 1 (HSV-1).
• It is the leading infectious cause of blindness in developed countries.

Causes & Risk Factors

• HSV-1 (cold sore virus): Most common cause
• HSV-2 (rare, typically in neonates)
• Primary infection OR reactivation from dormant virus in trigeminal nerve
• Reactivation triggers:
• • Previous ocular HSV infection
  • Immunosuppression
  • Corticosteroid eye drops
  • Trauma to the eye
  • UV light exposure
  • Stress, fever, or other illnesses

Pathophysiology

• Virus infects corneal epithelium → local replication → immune response and inflammation
• Classic sign: Dendritic ulcer ("branching" appearance) visible with fluorescein under blue light
• Damage from both direct viral effect & host immune response
• Recurrences due to latent virus in trigeminal ganglion

Symptoms

• Red, painful eye
• Photophobia (light sensitivity)
• Watery eyes (epiphora)
• Gritty/foreign body sensation
• Blurred vision
• Unilateral (usually one eye)

Mnemonic: Red,Sore, Light-Sensitive Eye

Signs (Examination)

• Dendritic (branching) ulcer on cornea (with fluorescein)
• Conjunctival redness
• Decreased corneal sensation
• Sometimes mild lid swelling
• Recurrent cases may have corneal scarring

Diagnosis

• Clinical: Dendritic ulcer seen with fluorescein staining and slit lamp exam is usually diagnostic
• PCR/corneal swab: Only in atypical, severe, or unresponsive cases
• Always consider Herpes Zoster Ophthalmicus, bacterial or fungal keratitis in differential

Epidemiology

• Incidence in UK: ~1 in 5,000 per year
• Common, especially in adults

Management

• Urgent ophthalmology referral (specialist management needed)
• Antivirals:
• • Topical aciclovir (or ganciclovir) ointment
  • Oral aciclovir in recurrent or severe cases
• Avoid corticosteroids (unless specifically prescribed by a specialist with antiviral cover, e.g., for stromal keratitis)
• Supportive: Lubricants for comfort
• Patient education: About recurrence risk and triggers

Prognosis

• Good if treated early—most recover with minimal long-term damage
• Recurrences are common
• Untreated/severe cases: Can lead to permanent corneal scarring, reduced vision, or even corneal perforation

Complications

• Corneal scarring
• Vision loss
• Corneal thinning/ulceration
• Neovascularisation (new vessels in cornea)
• Secondary bacterial infection
• Herpetic stromal keratitis (deeper inflammation)
• Corneal perforation (very rare)

Key Revision Resources (Full URLs)

• Revision Notes:
  https://www.passthemsra.com/topic/herpes-simplex-keratitis-revision-notes/
• Flashcards:
  https://www.passthemsra.com/topic/herpes-simplex-keratitis-flashcards/
• Accordion Q&A Notes:
  https://www.passthemsra.com/topic/herpes-simplex-keratitis-accordion-qa-notes/
• Rapid Fire Quiz:
  https://www.passthemsra.com/topic/herpes-simplex-keratitis-rapid-quiz/
• HSK Quiz:
  https://www.passthemsra.com/quizzes/herpes-simplex-keratitis/
• Main Ophthalmology/MSRA Revision Sites:
  https://www.passthemsra.comhttps://www.freemsra.com

🏁 Summary Takeaways

• HSK = HSV-1 infection of the cornea
• Classic dendritic ulcer (think branches on the cornea)
• Red, painful, light-sensitive eye
• Needs urgent specialist referral
• Antiviral therapy is mainstay
• Corticosteroids are dangerous unless prescribed by a specialist
• Recurrences are common, can lead to scarring/vision loss

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