Ulcers typically form on the eye as a result of an infection. They form on the area of the eye known as the cornea, which is the clear tissue that covers the iris and pupil. Infective corneal ulcers form as a result of bacteria, viruses or fungi. Corneal ulcers that arise without an active infection are known as Morren's ulcers. Any type of corneal ulcer causes severe eye pain, and it can lead to permanent vision loss.
According to the Archives of Ophthalmology, the average thickness of the human cornea is approximately 1/2 mm. This tissue is composed of five layers. The top layer, known as the corneal epithelium, is where the ulcer starts. If the epithelium becomes scratched, an infective microorganism can attach itself to the cornea and begin to reproduce, causing an active infection. The damage to the cornea results from the microorganism itself and from the eye's immune system fighting to kill the microorganism. If a scar develops over the pupil, the vision in the effected eye will be permanently reduced.
Bacterial Corneal Ulcer
Bacterial corneal ulcers are most commonly related to contact lens wear. Poor hygiene with the contact lenses or overwearing contact lenses can increase the risk of a bacterial corneal ulcer. Bacterial corneal ulcers will cause the eye to be red, painful and light sensitive. They generally affect one eye only and they are not contagious. Bacterial corneal ulcers are typically treated with an antibiotic eye drop.
Viral Corneal Ulcer
Viral corneal ulcers develop as a result of the herpes simplex type 1 virus. This is the same virus that causes cold sores on the mouth. The virus lies dormant in the brain stem. For the eye to become infected, the virus travels up the nerve that senses pain for the eye. When it gets to the eye, it causes a corneal ulcer to develop. This corneal ulcer only causes mild discomfort and watery eyes. The virus affects only one eye at time and is not contagious. Antiviral eye drops are the treatment. The herpes simplex type 1 virus is not related to the virus that causes genital herpes.
Fungal Corneal Ulcer
Fungal corneal ulcers most commonly develop as a result of eye trauma with plant matter such as a weed or tree branch. If the eye is poked with a weed or tree branch, fungal cells become attached to the cornea, and a corneal ulcer develops. These cause almost identical symptoms to the bacterial corneal ulcer. Antifungal eye drops will treat a fungal corneal ulcer. Unfortunately, the fungal corneal ulcers do not respond to treatment as quickly as a bacterial corneal ulcer.
A Morren's ulcer actually develops without the presence of an infection. The eye's immune system begins secreting enzymes that normally dissolve bacteria, viruses and fungi. In the absence of these microorganisms, the enzymes dissolve corneal tissue. This causes an ulcer to develop on the cornea. The Morren's ulcer causes the eye to be red, moderately irritated and light sensitive. Morren's ulcers are treated with anti-inflammatory eye drops such as corticosteroids.