“…As an example, the POAG phenotype may be defined in many different ways: by the associated traits (endophenotypes) cup‐to‐disc ratio (CDR), intraocular pressure (IOP), visual field (VF) loss, or by some combination of these (reviewed in Weinreb, Aung, & Medeiros, ). Fifteen loci have been identified as genetic risk modifiers of disease (Burdon et al., ; Chen et al., ; Cooke Bailey, Hoffman, et al., ; Gharahkhani et al., ; Hysi et al., ; Li et al., ; Thorleifsson et al., ; Wiggs et al., ), and numerous others identified in POAG endophenotypes have recently shown association with POAG (Gao, Huang, Nannini, Fan, & Kim, ; Khawaja et al., ; MacGregor et al., ). The genetic factors identified in studies of POAG and its component phenotypes (such as IOP, CDR, VF changes) overlap but are not identical.…”