This study aims to investigate a potential link between Obstructive Sleep Apnoea (OSA) and Open Angle Glaucoma (OAG); initially by determining whether the prevalence of OSA is higher in patients with OAG in comparison to people without glaucoma and if OSA is an independent risk factor for OAG. It will comprehensively phenotype glaucoma patients for variables that may be associated with both OSA and OAG.