In this study of HIV-positive patients with a CD4 count below 100 cells/μL presenting to a primary care HIV clinic, the presence of ocular symptoms and reduced visual acuity considerably increased the likelihood of having CMV retinitis (i.e., high positive likelihood ratio), but had low positive predictive value at the relatively low prevalence of retinitis found in this population. This evidence concerns the gene CD4 and cytomegalovirus retinitis.