Intraocular pressure (IOP): the pressure of the fluid inside the eye, measured in millimetres of mercury (mmHg).
Aqueous humour: clear fluid that nourishes the inside of the eye and creates the pressure.
Drainage angle: the angle between the cornea and the iris, where the aqueous humour drains away.
Trabecular meshwork: the fine, sieve-like drainage system in the angle.
Optic nerve / disc: the nerve “cable” to the brain; the disc is its visible entry point in the eye.
Visual field: everything the eye sees without moving.
Perimetry: the measurement of the visual field.
Tonometry: the measurement of eye pressure.
OCT: a painless scan of the optic nerve and retina (“optical ultrasound”).
Gonioscopy: the examination of the angle with a special contact lens.
Pachymetry: the measurement of corneal thickness.
Open-angle glaucoma: the most common form; the angle is open but drainage works poorly.
Angle-closure glaucoma: a form with a narrow or blocked angle; can occur as an emergency.
Normal-tension glaucoma: glaucoma despite “normal” pressure readings.
Cataract: clouding of the eye’s lens; a different disease from glaucoma.