While elevated IOP and aging remain primary risk factors [65,173], genome-wide association studies (GWASs) have identified several common susceptibility loci associated with POAG, including SIX1–SIX6 and CDKN2A/B (p16^INK4A^) [174,175].These variants confer modest risk and contribute to disease susceptibility in the general population, in contrast to rare, high-penetrance mutations such as those in Myocilin (MYOC) and optineurin (OPTN), which underlie monogenic, early-onset forms of glaucoma [176,177]. Here, CDKN2A is linked to open-angle glaucoma.