Infections of the Outer Eye

Published on 08/03/2015 by admin

Filed under Opthalmology

Last modified 08/03/2015

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4 Infections of the Outer Eye

VIRAL INFECTIONS

Viruses are a common cause of infection of the external eye where they produce a wide variety of disease ranging from mild transient conjunctivitis to more serious infections in which conjunctival or corneal involvement may lead to scarring and, in some cases, blindness. Adenovirus, picornavirus, herpes simplex virus and varicella zoster virus may all cause isolated conjunctivitis, but commonly patients have some corneal or eyelid involvement, thus serving to remind the clinician that the whole of the external eye and adnexae may be a target for the same infection. The spread of the virus to the eye may occur by direct inoculation from an infected source, from indirect transmission by fomites, or neuronal spread in the case of latent herpetic infection. Less commonly, viral eye disease may be part of a generalized viral infection in which the eye is only one of several organs involved (e.g. cytomegalovirus, rubella, human immunodeficiency virus (HIV) infection). Where no specific therapy exists for viral infection of the external eye symptomatic treatment is usually all that is required until resolution takes place. In cases where specific therapy exists, for example in herpes simplex or varicella zoster virus infections, early accurate diagnosis is essential so that treatment with an antiviral may be started early enough to influence the course of the disease.

ADENOVIRUS

Adenovirus infection may be due to a variety of different serotypes that can vary in their clinical presentation and epidemiology. Epidemic keratoconjunctivitis is associated with adenovirus serotypes 8 and 19, which produce a severe and highly contagious form of disease. Pharyngoconjunctival fever, associated with serotypes 3 and 8 also occurs in epidemic form when, as its name suggests, it is associated with upper respiratory tract infection. Sporadic disease has been associated with adenovirus serotypes 1, 2, 4, 5, 11, 13, 14, 15, 20, 21, 23, 24 and 29. Although the severity of adenovirus infections may vary considerably certain clinical features are common to the majority of cases.

A typical case of moderate severity presents with acute bilateral but unequal, swelling and erythema of the eyelids associated with conjunctival inflammation and a watery serous discharge. There may be associated pre-auricular lymphadenopathy, a history of contact with other similar cases or a recent illness of the upper respiratory tract. Although the conjunctival changes resolve over 7–14 days, patients are often left with ocular irritation and discomfort for several weeks. This is due to tear film changes secondary to conjunctival scarring or keratitis.

HERPES SIMPLEX

Herpes simplex infection of the eye may be the result of either primary or recurrent infection. Ocular disease, in common with herpes labialis, is usually caused by herpes simplex virus (HSV) type I, in contrast to genital infection which is associated with HSV type II. Primary infection affects hitherto unexposed individuals who have no immunity to the virus and is acquired following inoculation from an infectious source. It characteristically occurs in children and young adults up to the age of 15 years as after that age serological evidence of exposure to HSV is present in 50–90 per cent of individuals. In primary infection the lesions occur on the skin around the mucocutaneous junctions and are associated with regional lymphadenopathy. In the nonimmunocompromised patient the primary disease heals within 3 weeks although the virus then persists in latent form. In the immunocompromised patient generalized infection may occur requiring systemic antiviral therapy. Recurrent infection in the eye may take the form of blepharoconjunctivitis similar to that occurring in primary disease although it usually runs a shorter time course. However, corneal disease is more common with characteristic dendritic ulceration occurring in the epithelium with deeper corneal stromal keratitis or keratouveitis becoming more common with successive recurrent attacks.

Primary herpes simplex infection normally induces a specific antibody response with the production of IgM initially and later raised IgG levels which persist. Intracellular virus is not accessible to antibody and the role of the humoral response is mainly in limiting the spread of the virus during viraemia and promoting antibody-dependent cell-mediated cytotoxicity. There is good evidence that cell-mediated immunity plays an important role in combating HSV infection as protection against infection can be transferred to immunosuppressed animals by T lymphocytes but not by antibody and the disease is more severe where there is suppressed cell-mediated immunity. Herpetic disease may be more severe, and frequently bilateral, in patients with atopy.