the key for obtaining a diagnosis. This is especially important as some of these diseases such as inflammatory bowel disease, pancreatitis, and Whipple’s disease may be fatal if not treated.

Another important entity in this chapter is the retinal and choroidal manifestations of malabsorption syndromes, such as vitamin A deficiency, which is accompanied by nyctalopia. These manifestations are reversible with the supplementation of the specific vitamin or minerals, but an appropriate diagnosis needs to be made. These vitamin deficiency syndromes have become more prevalent in recent years in developed countries with the increase in bariatric surgery procedures, which are very often followed by malabsorption syndromes.

Many posterior segment inflammatory findings are often left as idiopathic, but it is important to keep in mind that they may be manifestations of gastrointestinal diseases. Because they are frequently nonspecific and variable, the clinician must have a high degree of suspicion regarding the possibility of any gastrointestinal disease, as different tests can be performed and specific treatment needs to be prescribed.

Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is an immunemediated chronic intestinal condition. It has been divided into two different types: ulcerative colitis (UC) and Crohn’s disease (CD).

It is thought that the disease is brought about by an abnormal immune response to certain microorganisms in a person with a genetic predisposition. Both diseases consist of chronic inflammation of the colon but they have different characteristics. Ulcerative colitis involves the large intestine and the colon and is often most severe in the rectal area, which can cause frequent diarrhea. By definition, ulcerative colitis only involves the mucosa of the intestinal wall. Crohn’s disease generally involves both the ileum and colon, usually in a discontinuous pattern. The inflammation in CD is transmural and can be associated with granuloma formation, severe scarring, and fistulas (not generally found in UC) [1].

Epidemiology

The incidence of IBD varies depending on the location and type of population. It is found more frequently in Europe and North America. In North America, the incidence is estimated at 1.3–2.2 cases per 100,000 persons/year for ulcerative colitis and 3.1–14.6 cases per 100,000 persons/ year for Crohn’s disease. Prevalence rates for UC in North America are estimated at 37–246 cases per 100,000 persons/year and at 26–199 cases for CD [2]. Incidence and prevalence rates in Europe are similar. IBD was thought to be rare in other locations, but its incidence is increasing in areas such as Japan, South Korea, Singapore, India, and Latin America, especially referring to cases of UC. The mortality ratio for UC and CD has been estimated to be 1.37 and 1.51, respectively based on a Swedish population [2]. Mortality generally occurs from complications in the first years of the disease or as a result of late-stage colon cancer.

The peak age of onset is 15–30 years, although there is a second peak from ages 60 to 80. In Crohn’s disease, men and women are equally affected, whereas in UC, men are slightly more affected (1.2–1.8 men per woman). Prevalence of the disease is also related to population type: Jewish populations have a higher prevalence, especially Ashkenazi Jews. It is also more frequently found in urban areas as opposed to rural populations, especially in people of higher economic status. Smoking has a different effect on the risk of developing IBD: nonsmokers have a greater risk for developing UC, whereas smokers have a twofold risk of developing CD. Oral contraceptives also seem to increase the risk of CD (odds ratio: 1.4). Appendectomy increases the chance of having CD but is protective against UC. IBD is frequently associated to immune diseases such as psoriasis, ankylosing spondylitis, and primary sclerosing cholangitis.

IBD is most likely related to certain genetic susceptibilities and therefore runs in families. A first-degree relative of a patient has a 10% chance of developing the disease, and this figure rises to 36% if the subject is the child of two parents with IBD.

A hereditary pattern seems to be more present in CD than UC [3].