Glaucoma is the second leading cause of blindness in the world, with open-angle accounting for two-thirds of those affected.
Frequently presents asymptomatically and may be identified on routine ophthalmic examination.
Intra-ocular pressure may or may not be elevated.
Optic disc cupping is diagnostic.
May lead to irreversible loss of peripheral vision and, later, of central vision if untreated.
Glaucoma is a neurodegenerative condition primarily due to dysfunction in outflow of the nutrient-rich fluid, aqueous humour that constantly flows through the eye. Aqueous humour, created in the ciliary body, passes through the pupil into the small area between the iris and the cornea, called the anterior chamber. The fluid then flows into the periphery of the chamber known as the anterior chamber angle. This angle is where the fluid travels through the trabecular meshwork and into blood vessels. Open-angle glaucoma is characterised by an anatomically open angle but with an obstructed and slowed drainage system outflow. The mechanism of blockage is unclear. A rise in increased intra-ocular pressure results, characterised by retinal ganglion cell damage, then peripheral vision loss in early disease and central vision loss in late disease. 
Consultant Ophthalmic Surgeon
University Hospital Southampton NHS Trust
NA has received honoraria for educational talks from Thea Pharmaceuticals and Allergan. These companies manufacture drops used in the treatment of open angle glaucoma.
Dr Nishani Amerasinghe would like to gratefully acknowledge Dr Robert B. Avery and Dr Michael N. Wiggins, the previous contributors to this monograph. RBA and MNW declare that they have no competing interests.
Associate Professor of Ophthalmology
Department of Ophthalmology
Jones Eye Institute
University of Arkansas for Medical Sciences
RAH declares that he has no competing interests.
Queen Margaret Hospital
RS declares that she has no competing interests.
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