Uveitis poses a serious public health concern, but, compared with its impact, what we know about this inflammatory disease is disproportionally small. Uveitis includes a group of diseases of the uveal structures—iris, ciliary body and choroid—and inflammation of any of these may be potentially vision-threatening. Experts note that its epidemiology is unclear, and its classification is difficult because its multiple presenting characteristics and signs are tough to identify. To estimate the prevalence and incidence of uveitis, researchers conducted a systematic review of the Medline, Embase and Cochrane databases for all time up to January 2019. They found wide variation in population-based estimates of uveitis epidemiology and noted that the conclusiveness of these studies was limited.

The literature review team appraised all studies that met the criteria with a grading system based on the Oxford Levels of Evidence. The researchers compiled detailed descriptions of the study populations and factors affecting the estimates.

A total of 49 retrospective population studies met the criteria, 22 of which were population-based and 27 hospital-based. They noted that there was “substantial” heterogeneity among the study populations and methods of ascertaining uveitis (e.g., definitions, results reporting). This variability was especially important in prevalence studies, the researchers noted. Data ranged from nine to 730 cases per 100,000. Incidence studies turned up a pooled incidence of 50.45 per 100,000 people. The researchers wrote that geographic region was an important explanatory factor for the variability among the studies.

“Based on the results obtained in this systematic review, it’s very difficult to draw definitive conclusions,” the researchers wrote. “The studies analyzed present a variable methodology, which hampers obtaining unified figures of prevalence and incidence of uveitis. It’s also important to note that the quality of the studies was medium-low.”

Hospital-based studies are limited by selection, classification bias and confounding, but offer valuable information on etiologies and other factors, the researchers noted. “Hospital-based studies can be highly biased due to the inclusion of more severe patients or the use of different tools for diagnosis and classification,” they said.

“Despite the observed variability and the subsequent difficulty of having reliable estimates, the obtained results provide an idea of the frequency of this disease,” the researchers wrote. “The large heterogeneity underlines the need to carry out population-based epidemiological studies, with a rigorous methodology, to have reliable estimates of uveitis in our environment if we want to adequately plan the derived care needs.” They stressed the importance of studying different etiologies to establish a map of the “real care needs” of uveitis patients.