Keratitis is the medical term for inflammation of the cornea. The cornea is the dome-shaped window in the front of the eye. When looking at a person's eye, one can see the iris and pupil through the normally clear cornea.
The cornea bends light rays as a result of its curved shape and accounts for approximately two-thirds of the eye's total optical power, with the lens of the eye contributing the remaining one-third. Only the very thin tear film lies between the front of the cornea and our environment.
The cornea is about 0.5 millimeter thick. The back of the cornea is bathed in the aqueous fluid that fills the anterior chamber of the eye. The cornea has a diameter of about 13 millimeters (½ inch) and, together with the sclera (the white part of the eye) forms the entire outer coat of the eye.
The symptoms of keratitis usually include pain, tearing, and blurring of vision. The pain may be mild to severe, depending on the cause and extent of the inflammation. Sensitivity to light may also be present. To the observer, the eye may appear red, watery, and if the cornea has extensive keratitis, the normally clear cornea may look gray or have white to gray areas.
The diagnosis of keratitis is made by an ophthalmologist (a physician who specializes in diseases and surgery of the eye) through a history and a physical examination. The history consists of questions documenting a past medical and ocular history and the symptoms specific to the current visit.
The eye examination will consist of checking your vision and careful inspection of the corneas using a slit lamp, which is a microscope with excellent illumination and magnification to view the ocular surface and the cornea in detail. Special dye in the form of eyedrops may be placed in the eyes to assist with the examination.
In cases in which infection is suspected, a culture may be taken from the surface of the eye for specific identification of the bacteria, virus, fungus, or parasite causing the keratitis. Blood tests may also be done in certain patients with suspected underlying disease.
Keratitis has multiple causes, one of which is an infection of a present or previous herpes simplex virus secondary to an upper respiratory infection, involving cold sores.
- Amoebic keratitis. Amoebic infection of the cornea is the most serious corneal infection, usually affecting contact lens wearers. It is usually caused by Acanthamoeba. On May 25, 2007, the CDC issued a health advisory due to increased risk of Acanthamoeba keratitis (AK) associated with use of Advanced Medical Optics (AMO) Complete Moisture Plus Multi-Purpose eye solution.
- Bacterial keratitis. Bacterial infection of the cornea can follow from an injury or from wearing contact lenses. The bacteria involved are Staphylococcus aureus and for contact lens wearers, Pseudomonas aeruginosa. Pseudomonas aeruginosa contains enzymes that can digest the cornea.
- Fungal keratitis (cf. Fusarium, causing recent incidences of keratitis through the possible vector of Bausch & Lomb ReNu with MoistureLoc contact lens solution).
- Viral keratitis.
- Herpes simplex keratitis. Viral infection of the cornea is often caused by the herpes simplex virus which frequently leaves what is called a 'dendritic ulcer'.
- Herpes zoster keratitis.
- Onchocercal keratitis, which follows O. volvulus infection by infected blackfly bite. These blackfly usually dwell near fast-flowing African streams, so the disease is also called "river blindness".
- Exposure keratitis — due to dryness of the cornea caused by incomplete or inadequate eye-lid closure.
- Photokeratitis — keratitis due to intense ultraviolet radiation exposure (e.g. snow blindness or welder's arc eye).
- Ulcerative keratitis
- Contact lens acute red eye (CLARE) — a non-ulcerative sterile keratitis associated with colonization of Gram-negative bacteria on contact lenses.
- Severe allergic response may lead to corneal inflammation and ulceration (i.e. vernal keratoconjunctivitis).
- Feline eosinophilic keratitis — affecting cats and horses; possibly initiated by feline herpesvirus 1 or other viral infection.
Treatment depends on the cause of the keratitis. Infectious keratitis generally requires antibacterial, antifungal, or antiviral therapy to treat the infection. This treatment can involve prescription eyedrops, pills, or even intravenous therapy. Any corneal or conjunctival foreign body should be removed.
Wetting drops may be used if disturbance of the tears is suspected to be the cause of the keratitis. Steroid drops may often be prescribed to reduce inflammation and limit scarring. This must be done carefully and judiciously, since some infections can be worsened with their use.
Contact-lens wearers are typically advised to discontinue contact-lens wear, whether or not the lenses are related to the cause of the keratitis.