Eye infections occur when harmful microorganisms — bacteria, fungi and viruses — invade any part of the eyeball or surrounding area. This includes the clear front surface of the eye (cornea) and the thin, moist membrane lining the outer eye and inner eyelids (conjunctiva). Many of the viruses, bacteria, parasites and fungi that invade the human body are also capable of attacking the surface or interior of the eye.
Infectious eye diseases can be categorised in two ways. Firstly, doctors normally refer to the part of the eye that is infected or inflamed. Conjunctivitis, for example, is an inflammation of the conjunctiva. Other possible locations of inflammation include the eyelid (blepharitis), the cornea (keratitis), the liquid inside the eye (vitritis), the retina and the blood vessels that feed it (chorioretinitis), or the optic nerve (neuroretinitis). These are just a few examples – the eye is a complex organ of many parts.
Secondly, eye infections are classified according to what is causing them. Ocular histoplasmosis syndrome (OHS), for example, is caused by a fungus (the condition is also called chorioretinitis). It generally attacks the blood supply of the retina on the inner rear surface of the eye.
Types of Eye Infections
- Pink Eye (conjunctivitis)
- Eye Stye
- Corneal Ulcer
- Herpes Simplex Virus
- Herpes Zoster (shingles)
Pink eye, or Conjunctivitis, is a common eye ailment that has affected many of us. It is caused by an infection or inflammation of the conjunctiva (the outermost layer of the eyeball). Pink eye can be caused by bacterial infections, viruses, or allergies. If pink eye develops, the sclera (white part of the eye) may become red or pink in colour. There may be discharge, which can irritate the eyes further. Often the condition appears in one eye and then spreads to the other. There are several types of pink eye, and most are contagious. Depending on which type of pink eye you have, symptoms may last between seven and fourteen days.
Also called hordeola, styes are bacterial infections that lead to the obstruction of oil-producing glands around the eyelashes or eyelids. Styes appear as small bumps on the upper or lower eyelids, eyelashes or conjunctiva. They occur in both sexes and to all ages. Styes are usually harmless and will go away on their own within one to two weeks, when your body fights off the infection. To prevent a stye in the eye, always wash your hands before touching your eyes and maintain good eye hygiene, especially if you wear contact lenses.
Many people confuse styes with chalazion. The two types of infections are similar; the difference is that chalazion develops under the skin and never appears with a head, while styes look like a pimple on the eyelid. Also, a chalazion is not painful and usually not accompanied by redness or tenderness.
- Redness accompanied by slight pain and tenderness.
- Swelling that usually appears as a bump. The head of the stye may be on the outer eyelid or underneath the eyelid.
- Discomfort when blinking; gritty feeling in eye.
- Sensitivity to light.
Blepharitis or Eyelid Inflammation
Blepharitis is a non-contagious and common eye disorder that affects all ages and both sexes, and may be associated with bacterial infection or skin disorders such as rosacea or seborrhea. It inflames the eyelash follicles along the edge of the eyelid, forming dandruff-like scales on the eyelashes.
Oil glands (meibomian glands) run along the edges of the eyelids, and when these glands become irritated or inflamed, the oil secretions thicken and do not flow properly. The meibomian secretions are an important part of a healthy tear film, and their absence can cause the tear layer to become unstable or evaporate quickly.
Although most experts treat it as a serious condition, blepharitis alone is not known to cause any permanent damage to one’s eyesight. If blepharitis is severe, then related problems affecting the cornea can be vision-threatening. Eye care professionals usually become aware of the condition in the course of comprehensive eye examinations.
There are many symptoms that may signal the presence of blepharitis or eyelid inflammation. Some of these symptoms are more severe than others, and sometimes a person will not experience any of these symptoms at all. The most common symptoms include:
- Crusty discharge on the lashes or lids, especially when first awakening
- Redness of the eye or eyelids
- Swelling of eyelids and skin around eyes
- Excessive tearing
- Dry eyes
- Blurring of vision
- Loss of eyelashes
- Photophobia (sensitivity to bright light)
- Gritty sensation when blinking
- Fluctuating vision due to secondary dryness and an unstable tear film
A corneal ulcer is an open sore or break on the cornea. The cornea is the clear, protective covering at the front of the eye and is the first part of the eye to refract light. A corneal ulcer is often the result of an untreated corneal abrasion (a scratch on the cornea). Once an injury or scratch occurs, bacteria immediately begin invading the wound, which leads to infection and corneal ulcers.
Corneal ulcers occur in people of all ages. Typically the ulcer is infectious, but some corneal ulcers are not. Pain, redness, and vision problems are usually associated with ulcers that contain bacteria. Still, all corneal ulcers should be looked at by an eye care professional, to ensure that there is no infection and to help craft an appropriate treatment plan.
Corneal Ulcer Symptoms
Symptoms of corneal ulcers vary from person to person, depending on such factors as the location and size of the ulcer. If the ulcer is caused by bacteria, it may be visible to the naked eye in the form of a white patch on the cornea. Not all corneal ulcers are visible, however, especially if they are caused by the herpes simplex virus (discussed more in the causes section). Typically, corneal ulcers cause symptoms such as:
- Pain, ranging from mild to severe, but typically severe
- Redness of the sclera (white part of eye)
- Photophobia (sensitivity to light)
- Impaired and/or blurred vision
- Watering of the eye
- Clouding of the eye
- Discharge from the eye
- Feeling of foreign body in eye
Causes of Eye Infections
Infectious conjunctivitis is the most common cause of pink eye around the world. Causes of infectious conjunctivitis are numerous and can usually be classified as viral, bacterial or fungal.
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. 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. People of African descent are largely immune.
Chlamydia and gonorrhoea: These extremely common sexually transmitted infections (STIs) can cause conjunctivitis, though they do not usually cause serious damage to the eye in adults. The infection gets into the eye either directly through genital fluids such as semen, or when infected people rub their eyes after handling 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 in the same way as chlamydia or gonorrhoea. Like these diseases, herpes 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. About 15 per cent of people with chronic ocular herpes simplex lose some vision.
Shingles (herpes zoster, varicella zoster): Shingles are a reactivation of the virus that initially causes chickenpox. The sores known as shingles are infectious and can cause chickenpox in others. They can also cause ocular infection if you touch the eyes after touching a sore. While herpes simplex is the leading cause of acute retinal necrosis in the young, varicella zoster is the leading cause in people over 50 years of age because shingles is more common in this age group.
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 cannot penetrate the outer layer of the eye, and cause only conjunctivitis. However, eye injury, lack of oxygen due to contact lenses, 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.
Infections that can damage the retina and the inner eye include
Varicella zoster (shingles and chickenpox)
Cytomegalovirus, which does not affect healthy people but is the leading cause of blindness in people with HIV/AIDS
Complication of Eye Infections
Serious complications of eye infection include damage to the retina and the formation of scars and ulcers in the cornea that can obstruct vision. Some infections, like syphilis, can also provoke glaucoma. Moreover, eye problems are often the only visible symptom of wider infections. Chlamydia, for example, often causes no genital symptoms, but can cause infertility and heart damage if left untreated.
Diagnosing Eye Infections
Ophthalmologists and optometrists are trained to recognise various eye infections by the appearance of the surface of the eye and the retina, the progress of the disease, whether it is in one eye or both, and your medical history.
You should see your doctor or eye care professional if you have:
- Eye pain, altered vision or severe redness of the eye;
- Continuous discharge from the eye;
- Recurring eye problems;
- Eye problems along with a chronic condition such as diabetes;
- Changes in pupil size;
- Recent injury to the eye.
You should also see your doctor or eye care professional if:
- You have been treating symptoms yourself for 48 hours and no improvement is noted;
- The condition worsens with treatment;
- The condition has lasted longer than 48 hours without treatment.
Treating and Preventing Eye Infections
Viral conjunctivitis usually improves in a few days without treatment. Broad-spectrum antibiotics 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 cannot even be detected in the retina, though we know it is there. The only current treatment is laser cauterisation of the affected area, which dramatically slows the destruction of the macula (the centre of the retina). This operation often has to be repeated several times. There is still no way to repair the damage already done, though new surgical techniques are under study.
Herpes simplex cannot be eradicated from the body, but flare-ups in the eye can often be fought off with antiviral medications. The problem may recur.
Serious diseases like tuberculosis, syphilis, and toxoplasmosis need to be treated for the body as a whole before eye problems will clear up.
There is 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 will 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.
Hand-washing is extremely important in preventing the spread of organisms that can cause infection. Sharing of towels, pillow cases, wash clothes and makeup should always be avoided to prevent spread of an eye infection.
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. Just as important is 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.
The same is true of cold sores, shingles, chickenpox, measles, mumps, flu, and the common cold. All of these diseases produce spots, rashes or mucus that carry the organism. Wash your hands frequently and do not touch your eyes. Watch children carefully and never let them wipe their nose with an upward stroke of the hand.
If you or a member of your family has an eye infection you should use separate linens and a fresh facecloth and towel for each cleaning. Cosmetics may be a source of recurrent infection, so avoid them if possible if you have eye problems. Be sure to clean the eye area, especially before applying any medication and when there is any type of discharge from the eye.
If you wear contact lenses, care for them and throw them away according to the manufacturer’s instructions.
Watch for tree branches and twigs when walking in the woods. Getting scratched on the eye by organic matter is another way of getting a fungal eye infection.
Finally, avoid excessive sun exposure, as this can weaken the protective layer of the eye.
Report compiled by Temitope Obayendo from EyeHealthWeb, Allaboutvision.com and chealth.canoe.ca