1) An ocular disease, occurring in many forms, having as its primary characteristics an unstable or a sustained increase in the intraocular pressure which the eye cannot withstand without damage to its structure or impairment of its function. The consequences of the increased pressure may be manifested in a variety of symptoms, depending upon type and severity, such as excavation of the optic disk, hardness of the eyeball, corneal anesthesia, reduced visual acuity, seeing of coloured halos around lights, disturbed dark adaptation, visual field defects, and headaches.

2) A disease of the eye marked by increased pressure within the eyeball that can result in damage to the optic disc and gradual loss of vision.