Intraocular pressure (IOP) is the fluid pressure inside the eye. Tonometry is the method eye care professionals use to determine this. IOP is an important aspect in the evaluation of patients at risk from glaucoma. Most tonometers are calibrated to measure pressure in millimeters of mercury (mmHg). ==Physiology== Intraocular pressure is mainly det...
<ophthalmology> The pressure the fluid (vitreous) contained within the eye, exerts on the globe (lining of the eyeball). Increased intraocular pressure is a feature of glaucoma. ... (27 Sep 1997) ... 
the pressure exerted against the outer coats by the contents of the eyeball; called also intraocular tension.
Type: Term Definitions: 1. the pressure of the intraocular fluid within the eye, measured by means of a manometer, usually in millimeters of mercury.
Intraocular pressure: The pressure created by the continual renewal of fluids within the eye. The intraocular pressure is increased in glaucoma. In acute angle-closure glaucoma, the intraocular pressure rises because the canal into which the fluid in the front part of the eye normally drains is suddenly blocked. In chronic glaucoma, there is a grad...
The pressure within the eye.
[n] - pressure inside the eyeball
the pressure of the fluids within the eye 
The pressure within the globe. IOP is increased in glaucoma.