The Water Drinking Test in Glaucoma Study

Inclusion Criteria: * Able to give informed consent to participate in the study * Aged between 18 and 80 years of age * Clear optical media * Spherical equivalent +-10 Dioptres * Normal tension glaucoma proven by visual field testing or OCT imaging combined with clinical assessment. * Primary open angle glaucoma proven by visual field testing or OCT imaging combined with clinical assessment. Exclusion Criteria: * Are using ocular hypotensive therapy, or have done so in the last 30 days * Have any other known ocular disease (except glaucoma) * Have serious cardiac or kidney disease (WDT contra-indication) * Have swallowing difficulties associated with either a neurological or gastrointestinal condition. * Patients with any contra-indication of drinking large amounts of water in a small period of time e.g. swallowing impairment, oesophageal stricture, gastric banding. * Have secondary or narrow/closed angle glaucoma * Patients submitted to any surgical procedure or laser intervention during the evaluation period