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Herpes simplex keratitis
Herpetic simplex keratitis is a form of keratitis caused by recurrent herpes simplex virus (HSV) infection in the cornea.
Keratitis caused by HSV is the most common cause of cornea-derived blindness in developed nations.
HSV is a double-stranded DNA virus that has icosahedral capsid.
HSV-1 infections are found more commonly in the oral area and HSV-2 in the genital area.
Ocular herpes simplex is usually caused by HSV-1.
It is estimated that one third of the world population have recurrent herpetic infections.
HSK begins with infection of epithelial cells on the surface of the eye and retrograde infection of nerves serving the cornea.
HSV infection of the eye typically presents as swelling of the conjunctiva and eyelids accompanied by small white itchy lesions on the corneal surface.
HSV infection effects ranges from minor damage to the epithelium to serious consequences such as the formation of dendritic ulcers.
Infection is unilateral.
Symptoms include dull pain in the eye, mild to acute dryness, and sinusitis.
Most infections resolve spontaneously in a few weeks.
Healing can be aided by the use of oral and topical antiviral agents.
Recurrent infections may be more severe, with infected epithelial cells showing larger dendritic ulceration, and lesions forming white plaques.
With recurrent infections the epithelial layer is sloughed off as the dendritic ulcer grows.
With recurrent infections inflammation may occur in the underlying stroma of iris, and sensation loss can occur producing generalized corneal anaesthesia.
Recurrent herpetic keratitis can be associated with chronic dry eye, low grade intermittent conjunctivitis, or chronic unexplained sinusitis.
With persistent infection the concentration of viral DNA reaches a critical limit, and an antibody response against the viral antigen triggers a massive immune response in the eye.
The immune response may result in the destruction of the corneal stroma, (immune-mediated stromal keratitis), resulting in loss of vision due to opacification of the cornea.
Approximately 1.5 million new cases worldwide, with about 40,000 cases of severe monocular visual impairment or blindness each year.
The primary herpetic infection most commonly manifests as blepharoconjunctivitis, involving lids and conjunctiva that heals without scarring.
Corneal involvement is rarely seen in primary infection.
Bilateral herpetic keratitis is particular really rare, will they reported incidence of 1-10%.
Bilateral involvement may be noted in patients with: atopy, measles, graft versus host disease, immunodeficiency and in younger patients.
Recurrence herpes infection of the eye is caused by reactivation of the virus in a latently infected sensory ganglion, transport of the virus down the nerve axon to sensory nerve endings, and subsequent infection of ocular surface.
The classic herpetic lesion consists of a linear branching corneal ulcer, described as a dendritic ulcer.
The defect manifests after staining with fluorescein dye.
Clinically, patients with epithelial keratitis complain of foreign-body sensation, light sensitivity, redness and blurred vision.
Reduction in corneal sensation develops following recurrent epithelial keratitis.
The ulcer may become large In immune deficient patients or with the use of corticosteroids.
Longstanding corneal edema leads to permanent scarring.
Scarring is the major cause of decreased vision associated with herpetic keratitis.
A clinical diagnosis of HSV as the cause of dendritic keratitis can usually be made based on the presence of characteristic clinical features.
Laboratory tests are indicated in complicated cases when the clinical diagnosis is uncertain and in all cases of suspected neonatal herpes infection.
Corneal smears or impression cytology specimens can be analyzed by culture, antigen detection, or fluorescent antibody testing to make the diagnosis.
Papanicolaou staining of corneal smears ( Tzanck smear) show multinucleated giant cells and intranuclear inclusion bodies.
The Tzanck smear test has low in sensitivity and specificity.
DNA testing is rapid, sensitive and specific.
Demonstration of HSV is possible with viral culture.
Serologic tests may show a rising antibody titer during primary infection.
Treatment of herpes of the eye is based on its presentation.
Epithelial keratitis is caused by live virus while stromal disease is an immune response and metaherpetic ulcer results from inability of the corneal epithelium to heal.
Epithelial keratitis is treated with topical antivirals for 10–14 days.
Acyclovir ophthalmic ointment and Trifluridine eye drops have similar effectiveness.
They are more effective than Idoxuridine and Vidarabine eye drops.
Oral acyclovir is as effective as topical antivirals.
Oral acyclovir has the advantage of no eye surface toxicity, and is pref2242ed by some ophthalmologists.
Ganciclovir and brivudine treatments were found to be equally as effective as acyclovir in a systematic review.
Topical corticosteroids are contraindicated in the presence of active herpetic epithelial keratitis.
Stromal herpetic keratitis is treated initially with prednisolone eye drops accompanied by a prophylactic antiviral drug: either topical antiviral or an oral agent such as acyclovir or valacyclovir.
Topical antiviral medications are not absorbed by the cornea through an intact epithelium, but orally administered acyclovir penetrates an intact cornea and anterior chamber.
Herpetic ulcers are treated with artificial tears and eye lubricants, stopping toxic medications, performing punctal occlusion, bandage contact lens and amniotic membrane transplant.