Examples of eye infections causing uveitis
Herpes virus infection:
The herpes group of viruses affects many people in various ways. Viruses which belong to this group are the type 1 and type 2 herpes simplex (Type 1 most commonly causes mouth “cold sores” and type 2 causes genital herpes), as well as the zoster virus which causes chickenpox and herpes zoster of the skin (“shingles”). Another member of this group of viruses is cytomegalovirus, CMV.
Herpes viruses are one of the commonest infections affecting the cornea or the internal eye structures. They typically cause keratitis (inflammation of the cornea) with or without uveitis (inflammation of the internal eye structures). The zoster virus tends to affect the eye when the skin of the eyelids and forehead is affected by “shingles”, a common condition referred to as herpes zoster ophthalmicus.
By nature, herpes viruses tend to stay in the body for life, occasionally becoming active and causing symptoms, then becoming dormant again for unpredictable periods. When active they are capable of creating a wide range of problems, from trivial discomfort and red eye, to severe eye damage.
The diagnosis of these viral infections is usually clinical (by examining the patient and the eye). In some cases there is uncertainty about the diagnosis and laboratory testing is necessary, taking samples from the surface of the eye or from the fluids inside the eye.
The treatment of herpetic infections relies on antiviral drugs which can be delivered to the eye either by eye drops, ointments or by using oral or intravenous antiviral medications. A typical example is acyclovir. These drugs are often effective in keeping the viruses less active and limit the damage they cause to the eye. However they do not completely cure the infection and do not eliminate the virus from the body. In patients with frequent recurrences there is often a need for long term treatment with antiviral medications (often by mouth), which may be required for months or years.
Patients with herpetic eye infections may develop a range of problems in the eye as a result of the infection. Examples include scarring and clouding of the cornea, paralysis of the pupil muscle, causing a permanently dilated and poorly reactive pupil, cataract, glaucoma and high pressure inside the eye, damage to the retina and optic nerve and retinal detachment.
Toxoplasma infections of the eye
Toxoplasma is a common parasite which lives in cats and affects many other mammals including farm animals. People get infected with this parasite in several ways, including through eating uncooked meat containing the parasite. Alternatively, it can be transmitted to the foetus from the mother through the placenta if the mother is infected with toxoplasma for the first time during pregnancy. Lastly, the parasite may contaminate food and water as it is present in cat faeces.
The parasite may cause a wide range of problems. In very young babies it may cause death or severe brain abnormalities. At an older age it can affect various organs and cause acute infectious symptoms, similar to those of a flu. If it infects the eye it can cause retinitis, inflammation of the retina. Depending on the location in the retina it may cause no visual symptoms or severe, permanent loss of vision. An active toxoplasma retinitis often presents with symptoms of redness, light sensitivity, floaters and hazy vision. It then settles down even without treatment over a couple of months or so, sometimes leaving the patient with floaters or other visual symptoms. It usually leaves a typical retinal scar which is very helpful in making the diagnosis. In patients with impaired immune system, such as AIDS patients, the disease may be more severe and may involve other organs like the brain.
Toxoplasmosis of the eye tends to be a recurrent disease. The parasite stays dormant in the retina, and may reactivate after various periods, even decades later.
Treatment of toxoplasmosis:
When patients present with active toxoplasma retinitis, they are often treated with oral antibiotics and steroids (cortisone type medications) for several weeks. In patients with “high risk” disease which is threatening the centre of the retina (the macula) there is an option of low preventive dose treatment with antibiotics for many years. Rarely, the retinitis causes severe problems requiring surgery, for instance retinal detachment.