This is a common and serious infection of the corneal epithelium by Herpes simplex virus type I. The virus lies dormant in the trigeminal nerve between attacks.

The resulting ulcer is visible with fluorescein staining and has a delicate branching pattern, hence the name dendritic ulcer. When clinically suspected definitive diagnosis can be arrived at using

• immunofluorescence assay (IFA) for HSV-1 antigen, and
• polymerase chain reaction (PCR) for HSV-1 DNA (1)

A herpes simplex keratitis may present as an irritable eye without serious discomfort. May present as 4 clinical entities (2)

• infectious epithelial keratitis ( with characteristic dendritic ulcers)
• neurotrophic keratopathy
• stromal keratitis
• endotheliitis (classified as disciform, diffuse, or linear)

Recurrence of herpes simplex keratitis is common and the same side is usually affected. If the corneal infection is more deep seated there may be corneal thickening and central opacification. This is called disciform keratitis.

Reference:

1. Br J Ophthalmol. 2004 Jan;88(1):142-4.
2. http://www.emedicine.com/oph/topic100.htm