The document discusses eye infections, their causes, symptoms, diagnosis, and treatment. It notes that many viruses, bacteria, parasites, and fungi can infect the eye. Eye infections are categorized based on the infected part of the eye or what is causing the infection. The most common eye infection is conjunctivitis caused by viruses or bacteria. Left untreated, eye infections can damage vision by affecting parts of the eye like the cornea, retina, or optic nerve. Diagnosis involves examining the eye and testing for infectious agents. Treatment depends on the cause but may include antibiotics, antivirals, or other medications. Prevention strategies include hand washing and safe contact lens use.

1. EYE INFECTION

2. Many of the viruses, bacteria, parasites, and fungi that can invade the
human body are also capable of attacking the surface or interior of the
eye. Infectious eye diseases can be categorized in two ways.
Firstly normally talk about the part of the eye that's infected or
inflamed. Conjunctivitis, for example, is an inflammation of
the conjunctiva, the membrane that covers the front surface of the eye
and the inner surface of the eyelid. 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 also classified according to what's causing
them. Ocular histoplasmosis syndrome (OHS), for example, is caused by
a fungus (the condition is a type of chorioretinitis). It generally attacks
the blood supply of the retina, on the inner rear surface of the eye.

3. The most common eye infection is conjunctivitis caused by
an adenovirus (a type of common cold virus). This type of infectious
conjunctivitis is sometimes called pinkeye and is most common in
children. Viral conjunctivitis is very contagious because the virus can be
spread from the eye to hands that then touch doorknobs and other
surfaces that other people use.
There are other causes of infectious conjunctivitis, such as bacteria
like Staphylococcus aureus. Bacterial infections occur most commonly in
children and tend to result in longer-lasting cases of pinkeye.

4. Causes
Infectious conjunctivitis is the most common cause of pinkeye 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. It's common in
river valleys around the world. 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 blindness.

5. 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.

6. 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 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.

7. Infections that can cause conjunctivitis or keratitis (inflammation of the cornea)
include:
the STIs syphilis, gonorrhea, chlamydia, herpes simplex, and hepatitis B
tuberculosis
leprosy
Lyme disease
acanthamoeba - a common parasite
crab lice - these tiny animals can live and breed in your eyelashes and are invisible to
the naked eye
Epstein-Barr virus or infectious mononucleosis
mumps, measles, influenza, or shingles
onchocerciasis (river blindness)
sarcoidosis - the cause of this condition is not clear, but it may be due to an infection
Mycosis (general name for fungal infections) - Candida, the fungus that causes thrush,

8. 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

9. Symptoms and Complications
Obviously, with so many possible causes, the symptoms of eye infection can vary a
lot. What a person feels generally depends more on where the infection is rather than
on what's causing it.
Common symptoms of conjunctivitis include:
 redness and itching
 discharge
 viral conjunctivitis: discharge is usually watery or mucous-like
 bacterial conjunctivitis: discharge is thick and can be white, yellow, or
green
 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

10. Unfortunately, diseases that damage the retina, the optic nerve, or the blood vessels
that feed them often cause no pain at all. The primary symptom is deteriorating
vision, which is usually stoppable but not reversible. That's why it's vital to get your
eyes checked regularly. One possible symptom of internal eye damage is floaters, tiny
fragments in the liquid inside the eye. You see tiny bubbles or dark spots slowly falling
through your line of vision. Everyone has a few floaters – you should only worry if you
notice a sudden increase in them.
Almost all eye infections accompany disease in some other part of the body, even if it's
just a cold. Some but not all of these diseases have clear symptoms. Be on the lookout
for eye pain or visual symptoms if you have any of the diseases listed in the "Causes"
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.

11. Diagnosis
Ophthalmologists and optometrists are trained to recognize various eye infections by
the appearance of the surface of the eye and the retina, the progress of the disease,
whether it's in one eye or both, and your medical history. There's a wide range of
lighted devices for looking at the cornea and retina.
If there's pus or discharge from the eye, it can be cultured to identify the organism.
Quite possibly, you'll also be tested for common diseases like chlamydia, gonorrhea,
and herpes simplex.
You should see your doctor or eye care professional if you have:
 eye pain, altered vision, severe redness of the eye, or 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
 sensitivity to light
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

12. 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.

13. 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.
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.
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. Be sure to wash your hands before putting them in.