Viral Keratitis

Viral keratitis is frequently caused by:

❖ Herpes simplex virus.

❖ Varicella-zoster virus.

Other rare causes include cytomegalovirus, measles virus, or rubella virus. Herpes Simplex Keratitis

Epidemiology and pathogenesis: Herpes simplex keratitis is among the more common causes of corneal ulcer. About 90% of the population are carriers of the herpes simplex virus. A typical feature of the ubiquitous herpes simplex virus is an unnoticed primary infection that often heals spontaneously. Many people then remain carriers of the neurotropic virus, which can lead to recurrent infection at any time proceeding from the trigeminal ganglion. A corneal infection is always a recurrence. A primary herpes simplex infection of the eye will present as blepharitis or conjunctivitis. Recurrences may be triggered external influences (such as exposure to ultraviolet light), stress, menstruation, generalized immunologic deficiency, or febrile infections.

Symptoms: Herpes simplex keratitis is usually very painful and associated with photophobia, lacrimation, and swelling of the eyelids. Vision may be impaired depending on the location of findings, for example in the presence of central epitheliitis.

Forms and diagnosis of herpes simplex keratitis: The following forms of herpes simplex keratitis are differentiated according to the specific layer of the cornea in which the lesion is located. Recurrences are more frequent in the stroma and endothelium.

Dendritic keratitis. This is characterized by branching epithelial lesions (necrotic and vesicular swollen epithelial cells, Fig. 5.8). These findings will be visible with the unaided eye after application of fluorescein dye and are

— Herpes simplex keratitis: dendritic keratitis.

— Herpes simplex keratitis: dendritic keratitis.

Fig. 5.8 Characteristic findings include branching epithelial lesions.

characteristic of dendritic keratitis. Corneal sensitivity is usually reduced. Dendritic keratitis may progress to stromal keratitis.

Stromal Keratitis. Purely stromal involvement without prior dendritic ker-atitis is characterized by an intact epithelium that will not show any defects after application of fluorescein dye. Slit lamp examination will reveal central diskiform corneal infiltrates (diskiform keratitis) with or without a whitish stromal infiltrate. Depending on the frequency of recurrence, superficial or deep vascularization may be present. Reaction of the anterior chamber will usually be accompanied by endothelial plaques (protein deposits on the posterior surface of the cornea that include phagocytized giant cells).

Endotheliitis. Endotheliitis or endothelial keratitis is caused by the presence of herpes viruses in the aqueous humor. This causes swelling of the endothelial cells and opacification of the adjacent corneal stroma. Involvement of the endothelial cells in the angle of the anterior chamber causes a secondary increase in intraocular pressure (secondary glaucoma). Other findings include inflamed cells and pigment cells in the anterior chamber, and endothelial plaques; involvement of the iris with segmental loss of pig-mented epithelium is detectable by slit lamp examination.

Acute retinal necrosis syndrome. Involvement of the posterior eyeball (see herpetic retinitis) for all practical purposes is seen only in immunocom-promised patients (e.g., recipients of bone marrow transplants and AIDS patients).

Treatment: Infections involving the epithelium are treated with trifluridine as a superficial virostatic agent. Stromal and intraocular herpes simplex infections can be treated with acyclovir, which is available for topical use (in ointment form) and systemic use.

H Corticosteroids are contraindicated in epithelial herpes simplex infections but may be used to treat stromal keratitis where the epithelium is intact.

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