Eye Infections

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Featuring content from MRI Clinic

  • The Facts








    Some of the most common causes of serious eye infection include:

    Ocular histoplasmosis syndrome (OHS): Histoplasmosis is a fungal infection of the lungs, which is caught by inhaling spores. It's common in river valleys around the world. It's far more common in the US than in Canada, and is concentrated in the Midwestern states located in the Ohio and Mississippi River valleys. Approximately 60% to 90% of people living in these areas have been exposed to the fungus during their lifetime. Most infections do not cause symptoms and resolve on their own. In a small fraction of cases, the fungus migrates to the retina many years or decades later. Once there, it damages the retina, particularly the macula (the vital centre part where the vision cells are most concentrated). It causes symptoms and retinal decay very similar to macular degeneration, and can destroy the central part of the field of vision. Although only a tiny minority of people with histoplasmosis go on to suffer OHS, the fungus is so common that OHS is a significant infectious cause of legal blindness in Americans between the ages of 20 to 40 years. Anyone with a history of histoplasmosis should see a doctor if they notice any changes in their vision.

    Chlamydia and gonorrhea: These extremely common sexually transmitted infections (STIs) can also cause conjunctivitis. The infection gets into the eye either directly through genital fluids such as semen, or when infected people rub their eyes after touching infected genital areas. Babies born to genitally infected women are at especially high risk of eye infection. Neisseria gonorrheae is one of the few bacteria capable of penetrating the protective layers of the eye, causing inner-eye infection.

    Herpes simplex: This widely prevalent virus can be caught as a skin disease (cold sores) or as an STI. Herpes viruses can infect the eye by touching an active lesion (cold sore or blister) then touching the eye. Herpes infections in the eye tend to infect the top layer but it can cause pitting and ulceration of the cornea. Chronic herpes infection, which is uncommon, can cause acute retinal necrosis (ARN), particularly in men. This causes a major destruction of retinal tissue, and causes dramatic damage to vision. Herpes simplex keratitis is a major cause of blindness worldwide.


    Bacterial keratitis: This is an infection of the cornea by common bacteria found on the skin and in the mouth and nose. Normally, these bacteria can't penetrate the outer layer of the eye, and cause only conjunctivitis. However, eye injury, lack of oxygen due to contact lenses, infection from using contact lenses too long, or a weak immune system can all facilitate entry into the cornea, the clear layer in the front of the eye. Fungi can cause fungal keratitis under similar circumstances.


    • tuberculosis
    • leprosy
    • Lyme disease
    • acanthamoeba - a common parasite
    • Epstein-Barr virus or infectious mononucleosis
    • mumps, measles, influenza, or shingles
    • onchocerciasis (river blindness)

    Infections that can damage the retina and the inner eye include:

    • syphilis
    • tuberculosis
    • toxoplasmosis
    • sarcoidosis
    • herpes simplex
    • varicella zoster (shingles and chickenpox)
    • gonorrhea
    • histoplasmosis
    • cytomegalovirus, which doesn't affect healthy people but is the leading cause of blindness in people with HIV/AIDS
    Symptoms and Complications


    Common symptoms of conjunctivitis include:

    • redness and itching
    • discharge
      • viral conjunctivitis: discharge is usually watery or mucous-like
    • feels like there is sand in the eye
    • crusting over of the eyelid

    Common symptoms of keratitis and other frontal eye infections are:

    • pain, itching, or sensation of a foreign body in the eye which is often sudden in onset
    • photosensitivity (aversion to bright light)
    • redness or small red lines in the white of the eye
    • discharge of yellow or green pus that may make the eyes crusty upon waking up – a possible sign of bacterial infection
    • tears
    • swollen eyelids
    • constant involuntary blinking (blepharospasm)
    • reduced vision




    Making the Diagnosis




    • recurring eye problems
    • eye problems along with a chronic condition such as diabetes
    • changes in pupil size
    • recent injury to the eye
    • sensitivity to light

    You should also see your doctor or eye care professional if:

    • the condition worsens with treatment
    • the condition has lasted longer than 48 hours without treatment
    Treatment and Prevention

    Viral conjunctivitis usually improves in a few days without treatment. Broad-spectrum antibiotic eye drops will deal with most cases of bacterial conjunctivitis or keratitis, while particular antibiotics are used to treat gonorrhea and chlamydia. All of these diseases can be cured.

    Most fungal and parasitic infections are also treatable by various medications. The exception is histoplasma, which can't even be detected in the retina, though we know it's there. The only current treatment is laser cauterization of the affected area, which dramatically slows the destruction of the macula (the centre of the retina). This operation is done in hopes of saving the existing vision, though in some cases it may cause some vision loss of its own. It often has to be repeated several times. There's still no way to repair the damage already done, though new surgical techniques are under study.

    Herpes simplex can't be eradicated from the body, but flare-ups in the eye can often be fought off with topical (surface-applied) or oral (taken by mouth) antiviral medications.  Corneal transplant may be necessary if there is severe scarring or vision loss from the infection. Serious diseases like tuberculosis, syphilis, and toxoplasmosis need to be treated for the body as a whole before eye problems will clear up.

    There's not much you can do to avoid a disease like histoplasmosis, unless you avoid endemic areas (areas where the fungus is found, such as river valleys). You'll notice, however, that a great many eye infections are actually complications of sexually transmitted or genital diseases such as syphilis, chlamydia, gonorrhea, crab lice, herpes simplex, thrush, and hepatitis B. If you have herpes simplex, avoid touching your eyes if you have an active cold sore or blister.


    You can cut your risk of eye infection by observing safe sexual practices. That means using condoms, and, ideally, limiting your number of sexual partners. It’s also important to get checked for STIs regularly, since many of these diseases can go unnoticed until damage has been done, and you can infect other people. If you do have one of these diseases, keep your hands clean and away from your eyes.



    If you wear contact lenses, care for them and throw them away according to the manufacturer's instructions. Be sure to wash your hands before putting them in.


    Finally, avoid excessive sun exposure by wearing sunglasses, as this can weaken the protective layer of the eye.

