IOP (intraocular pressure): The pressure created by the continual renewal of fluids within the eye. The normal IOP varies among individuals. The intraocular pressure is increased in glaucoma.
In acute angle-closure glaucoma, the intraocular pressure rises rapidly because the iris blocks the angle in the front of the eye where the anterior chamber fluid normally drains out.
In chronic glaucoma, there is a gradual imbalance between the production and removal (resorption) of the fluid in the back part of the eye (with supply exceeding demand).