Herpes Simplex Keratitis

Herpes simplex keratitis is the most common infectious cause of corneal blindness in developed countries. It is further classified according to the layer of the cornea that is affected: epithelial or endothelial.

Pathology

Dendritic corneal ulcer seen in herpes epithelial keratitis. By Imran kabir hossain, CC BY-SA 4.0.

Primary herpes simplex infection causes blepharoconjunctivitis and the virus remains dormant within the trigeminal nerve ganglion.
Subsequent reactivation of the virus lead to recurrent epithelial keratitis (secondary herpes simplex infection).
Herpes simplex endothelial (also known as disciform) keratitis is an autoimmune hypersensitivity reaction to the herpes simplex antigen and manifests differently to epithelial keratitis.

Investigations

Simplex keratitis is a clinical diagnosis but swabs can be taken for PCR/Giemsa stain.
Giemsa stain would show multinucleated giant cells

Epithelial vs Endothelial (Disciform)

	Herpes Epithelial Keratitis	Herpes Endothelial Keratitis
Presentation	Painful blurry vision and foreign body sensation	Gradual onset painless reduction in vision.
Examination findings	Early phase → stellate (star shaped) corneal ulcer Late phase → characteristic dendritic corneal ulcer (branching tree shaped). Fluorescein highlights ulcers in green Rose bengal stain highlights the ulcer margins in red/purple`	Circular corneal stromal oedema keratic precipitates Wessely ring (circular deposition of antibody-antigen complex in the cornea)
Mangement	Topical acyclovir Steroids contraindicated as they interfere with corneal healing	Oral acyclovir 400mg, 5 times per day Steroids can be used to curb inflammation, as long as there are no corneal ulcers that need healing

Herpes Epithelial Keratitis

Herpes Endothelial Keratitis

Presentation

Painful blurry vision and foreign body sensation

Gradual onset painless reduction in vision.

Examination findings

Early phase → stellate (star shaped) corneal ulcer
Late phase → characteristic dendritic corneal ulcer (branching tree shaped).
Fluorescein highlights ulcers in green
Rose bengal stain highlights the ulcer margins in red/purple`

Circular corneal stromal oedema
keratic precipitates
Wessely ring (circular deposition of antibody-antigen complex in the cornea)

Mangement

Topical acyclovir

Steroids contraindicated as they interfere with corneal healing

Oral acyclovir 400mg, 5 times per day

Steroids can be used to curb inflammation, as long as there are no corneal ulcers that need healing

Wessely ring is not specific to HSV keratitis, it is the circular deposition of an antibody-antigen complex, visible in the cornea

Herpes Zoster Ophthalmicus

Herpes zoster ophthalmicus is essentially shingles of the eye. It can be severe and needs prompt treatment.

Pathology

Primary infection of Varicella-zoster leads to chickenpox.
Secondary (re)infection leads to shingles (herpes zoster).
Shingles of the eye (CNV1 dermatome) is herpes zoster ophthalmicus.

Presentation

Dermatomal vesicular rash and neuropathic pain.
Hutchinson sign: Rash on tip of nose indicates a high probability of ocular involvement because the tip of the nose is supplied by the nasociliary branch of CNV.
Conjunctivitis and epithelial keratitis with non-ulcerative pseudodendrites that do not stain with fluorescein

Management

Acyclovir Oral 800mg 5 times per day