OBJECTIVE: To define sloping of the retina, a novel stereoscopic feature in primary open-angle glaucoma (POAG), and to evaluate its prevalence and associated risk factors in an African ancestry population. METHODS AND ANALYSIS: Digital stereo disc images were graded for sloping by trained non-physician graders. We defined a sloping retina as one that slanted downward towards the disc margin instead of existing on the same plane as the disc margin. A 'sloping retina' approached the disc margin at an angle along at least one-third of the disc's circumference. The ocular and demographic risk factors of sloping were evaluated by univariable and multivariable logistic regression models. RESULTS: The prevalence of sloping in eyes with POAG was 22.0% (95% CI 20.6% to 23.4%). In a multivariable analysis, compared with eyes without sloping, eyes with sloping were less likely to have disc haemorrhages (p=0.03) and more likely to have a tilted disc (p<0.001), larger cup-to-disc ratio ((defined as 0.7-1), p=0.002), grey crescent (p=0.02), nasalisation of the vessels (p=0.01), moderate or deep cup depth (p<0.001) and conical cup shape (p<0.001). Sloping was not associated with any demographic characteristics in the multivariable analysis. CONCLUSION: Associated with risk factors of advanced POAG, sloping presents as a novel feature that warrants further study to determine its mechanisms of development and prevalence in other study populations. Study limitations include: large difference in the number of eyes with and without sloping, potential morphological expressions of other phenotypes posing as sloping, impact of anatomical variability on grading, inherent biases when grading stereoscopic images and absence of a control or glaucoma suspect group. Future research into this phenotype in POAG patients might determine whether sloping retina is the result of or a precursor to glaucomatous damage, leading to a better understanding of POAG.