Despite the high prevalence of the LOXL1 variants in the general population, a much lower proportion of the population develops PEX, suggesting that in addition to LOXL1, other genetic, epigenetic and environmental factors may contribute to the development of PEX. Also, LOXL1 cannot help to identify those with PEX at increased risk for glaucoma development. Increased risk for glaucoma development in PEX patients who present with increased IOP may be related to other factors beyond IOP, contributing to increased vulnerability of the optic nerve to glaucoma development in the presence of PEX.