BCR and posterior uveitis: It has been shown that whilst HLA-A29 is detected in almost 96 % of patients with BCR, the positive predictive value of HLA-A29 as a screening test in patients with posterior uveitis remains less than 50 % due to the rarity of BCR (rare even within the posterior uveitis population) and the background prevalence of HLA-A29 in the rest of the population (eg up to 5 % for Caucasians as discussed earlier).