Infections Of The Eye - A Closer Look

Eye infections can entail anything from the irritation of infected eyelids, to potentially sight-losing infections of the cornea. To start out we'll take a brief look at the anatomy of the eye.

The majority of the eye, about 5/6ths, is enclosed within the bony orbit. So only a small part is exposed to the environment. The most external parts of the eye are the eyelids, the conjunctiva and the cornea. The conjunctiva is the mucous membrane that lines the eyelid and extends to the surface of the eye. Inside the eyeball cavity are two fluid substances, the aqueous and vitreous humor. Infections can also occur in the tear duct system.

The eye does have several defense mechanisms to prevent infection and other foreign material from entering. The eyelashes are one defense mechanism. The tear ducts excrete antimicrobial enzymes called lysozyme and antibodies, which cleanses and protect the eye surface while also keeping it lubricated.

Infectious agents can attack any part of the eye, from inside or outside the body. From the inside, bacteria can reach the eye from the bloodstream from another site of infection. Also the close proximity to the sinuses lend to possible infections. There is some sparse microbial flora in the conjunctival sac including Staphylococcus epidermidis and Lactobacillus sp. being the most common.

The infections are:

* Blepharitis

This is an infection or inflammation of the edges of the eyelids. It may cause irritation, redness, burning and maybe itching. Staphylococcus aureus is the most common organism implicated.

Blister-like eruptions can be caused by Herpes simplex virus (HSV). These eruptions typically crust and heal within two weeks. In addition the pubic louse, Phthirius pubis has an affinity for eyelash hair causing irritation.

* Conjunctivitis

This is by far the most common type of eye infection. Age is a key factor for determining the causative microorganism. In newborns, gonorrheal and chlamydial infections are most common due to acquisition through the infected vaginal canal. The use of antibiotic drops has made these infections pretty rare in the United States.

Young children most frequently get bacterial conjunctivitis (pink eye) from Haemophilus influenza and Streptococcus pneumoniae. Both organisms are responsible for outbreaks of conjunctivitis. Symptoms depend on the offending organism but can include: swelling, redness, and discharge.

Numerous other bacteria can cause conjunctivitis. So can fungi rarely. Viruses are also an important cause with the adenoviruses being most common.

* Keratitis

These types of infections typically follow some sort of trauma to the cornea. Keratitis is an emergency situation because loss of vision can occur within 24 hours. There may be a decrease in vision and the presence of discharge is variable. Most causes of keratitis are bacterial (65-90%) with Pseudomonas aeruginosa and Staphylococcus aureus being most common. The most common viral pathogen is HSV.

An increasingly more common cause of keratitis is the amoeba, Acanthamoeba. This is most common in users of soft and extended wear contact lenses.

* Endophthalmitis

This is an infection of the intraocular contents of the eye. This is typically seen after surgery or some type of trauma. Numerous types of bacteria and fungi have been implicated in this relatively rare ocular infection. However, this disease can develop suddenly and progress rapidly to blindness.

* Infections of the lacrimal appartatus

These infections include canaliculitis (lacrimal canals), dacryocystis (lacrimal sac) and dacryoadenitis (lacrimal gland). These infections are caused by various bacterial and fungal organisms.

This is not an exhaustive list by any means. Some of the most serious and common causes of blindness are river blindness and trachoma, however these infections are rarely if ever seen in this country.

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