During preliminary testing, your doctor may have you capture the patient’s intraocular pressure. Intraocular pressure is the pressure of the fluid within the eye measured in millimeters of mercury. The pressure of the eye depends largely on the amount of fluid that is secreted into the eye and by the ease of which it leaves. The rate of the fluid exiting the eye or the fluid outflow is the single most important factor in regulating the eye pressure. Increased intraocular pressures can indicate occlusion.