Corneal Ulcer

Corneal Ulcer (Introduction)

The eye is one of the vital organs in a human being. As seen on figure 1, the eye is composed of many different parts and function. The cornea is a clear covering over the colored iris and the pupil of the eye. The function of cornea is to help focus light on the retina and protect the iris, lens, etc. so that the eye can see. The cornea is best to compare with a standard contact lens. Although, the function of a cornea is to protect from harmful microorganisms, it is also vulnerable to those same unicellular organisms.

One of the major diseases affecting the cornea is a corneal ulcer. A corneal ulcer is an "non-penetrating erosion, or open sore in the outer layer of the cornea, the transparent area at the front of the eyeball" (Medlineplus). Corneal Ulcer has many different names, depending on the microorganism that causes the ulcer. Some of the major diseases include Bacterial Keratitis, Fungal Keratitis, Acanthamoeba Keratitis, and Herpes Simplex Keratitis. Bacteria, fungi, amoebae, and viruses are the prime cause for these diseases. These microorganisms settle in the cornea, grow, and feed on the cornea. This process causes a corneal ulceration. Contact lenses are the leading way these microorganisms enter the cornea (discussed later).

There contains multiple symptoms in order to identify corneal ulceration. Some of these symptoms include the following: eye redness, tearing increases, vision impairs, eye burning, itching, and photophobia (sensitive to light) start to develop (Medlineplus).

Many different methods of detecting corneal ulcer are present at the doctor's office. Visual acuity test, Slit-lamp test, and Shirmers (tear) test are some of the tests that a doctor conducts during eye examination. Visual acuity test allows the doctor to measure a person's vision by reading the eye chart (figure 6). A Slit-lamp is a specialized magnifying microscope in which a doctor could examine the cornea, iris, and retina. Its use is to look in the interior of the eye with the built-in laser and a camera (figure 7). Shirmers test determines whether or not there is enough tears to keep the eye moist. Another methods of detecting for corneal ulcer are Keratometry (measurement of the cornea) and scraping of the ulcer for analysis (Medlineplus).

There are many different ways to treat corneal ulcer. Many times, corneal ulcer is treated in the doctor's office using eye drops. The eye drops are used to treat minor corneal ulcers. Depending on the microorganism that causes that corneal ulcer, many different varieties of eye drops can be used. If the ulcer is very severe, a particular surgery needs to take place. Either cornea transplant or Amniotic Membrane Transplant (AMT) needs to take place (Medlineplus). The treatments are thoroughly stated later.

Bacterial Keratitis (Figure 3)

Bacterial keratitis is caused by a variety of bacteria, and it is one of the most virulent forms of corneal ulcer. It rapidly grows on the cornea, and some bacteria destroy a cornea in 24-48 hours. Some of the most common bacterial species associates with bacterial keratitis are the following: Streptococcus, Pseudomonas, Enterobacteriaceae (including Klebsiella, Enterobacter, Serratia, and Proteus), and Staphylococcus (Murillo-Lopez).

Many species of bacteria often enter the cornea because of an abnormal tear in the corneal epithelium tissue (Murillo-Lopez). Many bacteria have structure that aids them to take control of the host cell. In the initial stage, the invasion of the bacteria causes inflammation in the infected area. As it progresses, necrosis starts to develop. Necrosis is a death of a tissue in response to a disease or an injury (Medical Dictionary). The inflammatory products (pus) diffuse and cause hypopyon. Hypopyon is accumulation of pus that appears gray fluid between the cornea and the iris (Medical Dictionary). Different bacteria also produce several enzymes, such as elastase and alkaline protease. They excrete the enzymes and cause harm to the cornea (Murillo-Lopez).

Bacterial keratitis causes other major problems to also occur in the cornea. Such problems can lead to major complications and even loss of vision. Corneal leukoma, irregular astigmatism, and corneal perforation are three of the major complications that occur during bacterial keratitis. Corneal leukoma is when scar tissue starts to form over the infected area at the end of bacterial keratitis. It can be managed through surgery such as phototherapeutic keratectomy (PTK) or penetrating keratoplasty (PK). These surgeries are done in extreme cases and will be discussed later. Irregular astigmatism is another complication that takes place when the healing is uneven. Astigmatism occurs when the light rays are focused in more than one place in the retina (Medical Dictionary). It can be resolved through contact lens, glasses, or surgery. Corneal perforation is the most dangerous complication because it threatens the loss of an eye. These three complications can occur even after bacterial keratitis begins to heal (Murillo-Lopez).

Bacterial keratitis can be caused by many different factors. By far, contact lens users are the number one cause for bacterial keratitis or any other forms of corneal ulcer. 8,000 cases per year relate contacts to bacterial keratitis. The second main cause is the lack of immunologic defenses. This lack is the secondary effect of alcoholism, malnutrition, and diabetes (Murillo-Lopez). Previous injuries or diseases in the eye play a major role in causing bacterial keratitis. In few cases the position and alteration of the eyelids also plays an important role in causing bacterial keratitis. These alterations may cause irritation in the cornea and even rupture it. Once the cornea ruptures bacteria starts to invade and cause bacterial keratitis.

A corneal specialist does many lab studies and imaging studies to find out information on the particular corneal disease. They may scrape the corneal ulcer and send it in for a culture to find out which microorganism is causing the ulcer. They use microscope slides and use Gram or Giemsa stains in order to classify the particular bacteria causing the keratitis. Doctors often take samples of eyelids, contact lens, or lens solutions to also find the origin of the keratitis. In imaging studying, doctors often use a slit-lamp or B-scan ultrasound. Slit-lamp photography is very useful in examining the progress of the keratitis (figure 7). To examine the regions that are not clearly visible, the doctor often uses B-scan ultrasound system. These studies give a better view of the factors that causes bacterial keratitis (Murillo-Lopez).

Bacterial keratitis