Virus infection of the eye Flashcards
keratitis
infection of the cells covering the surface of the cornea
conjunctiva
membrane covering the inner surface of the eyelid and the sclera of the eye
keratoconjunctivitis
infection of both the corneal surface and the conjunctiva
Herpesvirus infection of the eye: What are factors that allow the virus to infect the eye
Certain viruses of the herpesvirus family can cause primary and recurring infections of the eye. The exact nature and frequency of the recurrences seems to depend, in part, on the strain of herpes simplex virus that causes the primary infection as well as the immune status and general health of the individual. Note: HSV1 and HSV 2 exist in a variety of strains that differ in their pathogenicity. Herpes simplex virus (HSV) will serve as the primary point of discussion. Recall HSV exists as two types, 1 and 2.
Latent stages. Where do the HSV hide.
After primary infection, HSV induces a latent infection in the trigeminal ganglia (usually HSV 1) or in the sacral ganglia (usually HSV 2). In the case of trigeminal latency the virus can be reactivated from the latent state, travel down the ophthalmic branch and cause secondary infections of the eye.
Anatomy
Primary and recurring infections of the eye by HSV may cause various disease manifestations . In certain situations the viral infection can be exacerbated by an immuopathological attack against the eye. Different anatomical features of the eye may be involved in the infectious process. Recall (see diagram) that the outermost layers of cells covering the cornea constitute the epithelium. Underneath the epithelium is the stromal layer which is composed of keratocytes (fibroblastoid) and an orderly array of collagen fibers. The parallel alignment of the fibers ensures optical clarity and maximum transmission of light.
The innermost layer of cells is the endothelial layer which functions as a osmotic pump to keep the stromal layer dehydrated. If the stromal layer is no longer functioning, the stroma become hydrated and assumes a milky white appearance contributing to corneal blindness.
dendritic keratitis
Primary HSV infection of the cornea begin with replication of the virus in the epithelial cells. The pattern of infection varies depending on the strain of HSV 1 and HSV2 that initiated the infection. Some strains cause a pattern of cell destruction that looks like a “winding stream” or a dendrite and this is referred to as dendritic keratitis. The ophthalmologist can best visualize these lesions using a fluorescent dye and shinning a blue light on the eye to observe the fluorescent lesion.
Alternatively Rose Bengal can be applied to the eye and this causes the lesion to appear pink in color. A special device, slit lamp microscope, can help observe the lesions optimally.
geographic ulcers
Some strains of HSV cans cause broader lesions on the surface of the eye, which has been label geographic ulcers because they look like a continent on the surface of the earth.
stromal ulcers
After the primary HSV infection resolves, the individual may have recurring infections over time.
Some HSV strains, in conjunction with immunological based pathogenicity occurring in the patient, may cause the development of infections that involve infection of keratocytes in the stromal layer of the cornea. This leads to stromal ulcers. When the infection resolves the keratocytes synthesize new collagen fibers that are not arranged in an orderly array, i.e. scarring. After repeated stromal infections the scarring may be significant and cause loss of visual acuity.
corneal melting
One of the most severe manifestations of eye disease is called “corneal melting”. This appears to have an immunopathological basis whereby the immune systems attacks the stromal layer of the cornea. Following HSV infection the antigens of the virus that are present in the stroma elicit infiltration of the stroma by PMNs which are activated to produce complement and other products. Macrophages and activated T cells follow which causes further damage. In some cases treatment with steroids can exacerbate the destruction. The endothelial cell layer is often destroyed and the corneal becomes hydrated.
candidates for corneal transplants
Patients with advanced corneal scarring and corneal melting are candidates for corneal transplants. However, the latent virus is still resident in the trigeminal ganglia and its reactivation can start the infectious process of the cornea all over again.
Iridocyclitis
results form HSV infection of iris and surrounding tissues . Inflammation, sensitivity to light, blurred vision, pain, and eye redness.
Herpes retinitis
possible by rare in occurrence.
Herpes varicella-zoster virus
cause an infection of the conjunctiva primarily but it can also involve a corneal infection. Herpes zoster ophthalmicus can also establish a latent infection in the trigeminal ganglia and reactivate to cause recurring infections. This may include keratoconjunctivitis, uveitis and optical nerve palsies.
CMV (Herpesvirus)
also cause a chorioretinitis following the infection of the fetus as a result of a congenital infection. This may result in cataract formation and microphthalmia. In AIDS patients CMV has been shown to cause chorioretinits
