New evidence suggests that bacteria produced in the gut may be responsible for a condition known as uveitis. Uveitis is an inflammatory eye disorder that attacks the uvea, the part of the eye that comprises the iris, ciliary body, and choroid. Symptoms of this autoimmune disorder include eye pain, redness, blurred or decreased vision, light sensitivity, and the appearance of a hypopyon (whitish area) on the iris. Corticosteroids, such as Durezol, are typically prescribed to treat this disease because of their anti-inflammatory properties.
Types of Uveitis
There are several types of autoimmune uveitis, each marked by where it occurs:
• Irisitis – occurs in the front of the uvea (also called anterior uveitis)
• Pars planitis – uveitis that occurs in the middle section of the uvea
• Posterior uveitis – exists when the back part of the uvea is affected
• Panuveitis – all layers of the uvea are affected
One of the most significant problems with this disease is that it can be slow to develop and detect, and may linger for months or years. Because patients cannot use corticosteroids for extended periods, there is a need for greater understanding of what causes autoimmune uveitis to develop safer, more effective treatments.
Irisitis Anterior Uveitis Diagram
Causes of Uveitis
Autoimmune uveitis, which causes more than ten percent of all severe visual disabilities, is caused by an individual’s immune system attacking the eye; viruses, systematic inflammatory diseases (Crohn’s disease, etc.) and fungus (rarely) are some examples.
However, one of the problems with understanding this disorder and treating it is the nature of the eye itself, as it is one of the organs that is protected from the rest of the body by a blood-tissue barrier that mitigates the back-and-forth movement of blood-borne cells and other substances. The ability to understand what triggers autoimmune uveitis is the key element in developing more effective long-term therapies and, perhaps, a means of preventing it.
Gut Microbiota and Uveitis
Scientists have been puzzled about this breach of the blood-tissue barrier for generations. However, recent research conducted by the National Eye Institute (NEI) may have found an answer. Their results indicate that bacteria, viruses, and fungi in the gut may program immune cells (T cells) to seek out certain proteins found only in the eye and penetrate the ocular barrier. According to the research, bacteria in the gut produce a molecular protein that T cells identify as a protein in the retina, conditioning them to its presence. Bacteria can then begin to search out and attack the retinal protein.
While the implications of this research have yet to be fully determined, the study does provide more information that can contribute to solving not only the problem of autoimmune diseases of the eye but other areas of the body as well. If gut-activated T cells precede an autoimmune disease or disorder, it may eventually be possible to identify the specific bacteria involved and develop targeted treatment and therapy.