Glaucoma is a neurodegenerative disease of the optic nerve (optic neuropathy) and is characterised by the progressive, irreversible loss of retinal ganglion cells resulting in irreversible visual impairment and eventual blindness. Glaucoma is the most common optic neuropathy, with a global prevalence of 3.5% in people above the age of 40 years.1 There are many other causes of optic neuropathy, and these can easily be mistaken for glaucoma. This article will consider various ways that clinicians can differentiate between these by means of history taking, examination, investigations, and observation.