Mycotic Keratitis

The cornea plays an important role in vision. It not only protects the eye from dust, pollen, water, and other substances we come in contact with, it also helps focus light waves on the retina so that we can see. And because the light we rely on for vision must first pass through the cornea, the cornea must remain crystal clear for our vision to remain sharp.

One of the threats to the cornea is infection from fungi, bacteria, and viruses. Because the cornea does not have its own blood supply, the cornea is vulnerable to infection. It has recently been discovered that Renu contact lens solution (manufactured by Bausch & Lomb) has increased the risk of corneal fungal infections. Infections or the cornea are difficult to treat, and if treatment is unsuccessful, a corneal transplant may be necessary.

Corneal Fungal Infection (mycotic keratitis) has been in the news because many people who have used ReNu® with MoistureLoc® multi-purpose contact lens solution have reported problems. The Centers for Disease Control and Prevention (CDC) recently discovered that contact lens wearers who use this cleaning and storage solution made by Bausch and Lomb are at a greatly increased risk for a particular type of corneal fungal infection: fusarium keratitis.

At this time it is not known whether the solution itself is infected with the fusarium fungus or the chemicals in the solution adversely affect the eye, making individuals more susceptible to a fusarium infection, which is a common cause of fungal keratitis.

This site is devoted to information about corneal fungal infections, their symptoms, causes and treatment. If you or a loved one has been affected by this issue, we are here to help.

What is Mycotic Keratitis?

"Mycosis" is a fungal infection and "keratitis" is inflammation of the cornea. Therefore, "mycotic keratitis" is a fungal infection of the cornea.

The cornea

The cornea is the clear, curved tissue that covers the front of the eye (which is on the left in the diagram).

Unlike most tissues in the body, the cornea contains no blood vessels. It must instead rely on tears and the watery material immediately behind the cornea (the aqueous humor, which is located in the anterior chamber - the grey area behind the cornea in the diagram) for the nutrients and oxygen that the blood supplies to other parts of the body. White blood cells, which are an important part of our bodies immune systems, are also ordinarily carried in the blood and can only reach the cornea through either tears or the aqueous humor.

The cornea plays an important role in vision

The cornea plays two extremely important roles. The first is protecting our delicate eyes from whatever they come in contact with, whether it be water, dust or microscopic bacteria, viruses, and fungi. The cornea is also vital to our sense of sight. The cornea must remain transparent if we are to see clearly. The light we use with our sense of sight first passes through the cornea on its way to the retina in the back of the eye. Our retinas contain cells that send signals to our brains when they are struck by light, allowing our brains to integrate hundreds of millions of signals from the retinas into what we see. If the cornea is in the least cloudy, it will interfere with the clarity of our vision.

The cornea also plays a role in causing light to bend (refract) so that it is focused properly on the retina.

Light Refraction

In diagram A, light rays are bent at too great an angle, causing the rays to focus in front of the retina (the retina is on the very back of the eye). People who are near sighted (“myopia”) have a fuzzy or blurry image because light is focused in front of the retina. In an eye in which the cornea and the natural lens of the eye (the gray object behind the cornea in diagrams A and B) work together to focus light precisely on the retina, vision will be sharp. Diagram B shows light focused precisely on the retina (in this case with the aid of glasses, which are represented by the grey lens in front of the cornea). In people who are near sighted contact lenses (or glasses) change the angle at which light is refracted so that light is focused on the retina.

Treatment of Mycotic Keratitis

Antibiotics

Antibiotics are ordinarily the first treatment for a corneal infection. While antibiotics typically reach an infected area in the blood, the cornea has no blood supply. Therefore, treatment begins with drops applied directly on the cornea (“topical” treatment). Natamycin (Natacyn) is often the first drug used, while Amphotericin B is an alternative. However, fungi frequently infect the entire thickness of the cornea, and antibiotics may not penetrate into the inner corneal layers. When topical treatment alone is ineffective, a drug such as fluconazole may be added, which is taken by mouth. An oral drug enters the bloodstream from the intestines and can be carried in the bloodstream to the eye, where it will (hopefully) permeate through the aqueous humor to reach the cornea.

Surgery

Corneal Scraping

When antibiotic treatment fails, or when the cornea has been damaged before treatment is begun, some type of surgery may be necessary. In some cases superficial ulcers on the surface of the cornea can be treated by scraping the surface with an instrument. The surface of the cornea heals quickly and usually without scarring.

Keratectomy

If the ulcer or other injury is deeper, a keratectomy may be necessary. A deep corneal injury may lead to scar tissue that creates opacities (spots that aren't clear) which can block light rays from reaching the retina. A surgeon cuts the cornea to reach the area of scarring and then removes opacities and areas of infection using a microscope.

Phototherapeutic keratectomy (PTK)

Some surgeons are now using an instrument (a microkeratome, seen in the picture below) that slices the cornea at a predetermined depth.

The top of the cornea is not completely removed, allowing the flap to be folded back.

A very fine laser is then focused on the opacity, destroying (vaporizing) it without harming the surrounding tissue.

The flap is then folded back into place. The laser can also remove ulcers and other irregularities on the surface of the cornea. In most cases the body's response to the removal of corneal tissue is to replace it with new cells that are clear. PTK uses instruments and equipment also used in LASIK, a common surgery used to correct vision in people who are near-sighted.

Corneal transplants

If the infection has caused irreparable damage to the cornea, the cornea may be so cloudy that a corneal transplant is necessary. The surgeon removes the central portion of the cloudy cornea and replaces it with a donated clear cornea.

Donated corneas are obtained from an eye bank. Corneas are donated to an eye bank by individuals who have agreed to donate organs before they die or by family members of a loved one who has recently died. Following surgery eye drops that promote healing are used for several months. Stitches used to hold the cornea in place may be left in place for a number of months, but they can be easily removed in an ophthalmologist's office.

Even thirty years ago corneal injuries and infections frequently resulted in blindness. However, the now common use of microscopes in the operating room and the development of sutures (stitches) that are finer than a human hair – and are much less irritating to delicate and vulnerable corneal transplants – have made corneal transplant surgery commonplace. Forty thousand corneas are transplanted in the United States every year.

Potential complications of transplant surgery

Although most corneal transplant surgeries are successful, about twenty percent of transplant patients will reject the new cornea. In those individuals the body's immune system recognizes the new cornea as foreign and attacks it. When a corneal transplant is being rejected a person may experience symptoms similar to those of an infection, including decreased vision, eye redness, and pain.  If symptoms of rejection are promptly reported to a doctor and treated with medications that suppress the immune system (steroids), the transplant can often be saved. One study has also found that if the blood type of the donor of the cornea is matched with the blood type of the person receiving the transplant, there is less of a chance that the cornea will be rejected.