Ocular tension is often referred to as intraocular pressure. It is the pressure of the gel-like fluids, such as the aqueous humor and the vitreous humor, against the tunics of the eye. The tunics are the protective layers around the eye and are known as the sclera, choroid and retina. A normal pressure of these fluids against the tunics is essential, because it is the force that gives shape to the eyeballs. Excess or reduced pressure however can lead to problems such as ocular hypertension or ocular hypotony.
The vitreous humor is the gel-like fluid between the lens and the retina, and its main function is to maintain the shape of the eye. Between the lens and cornea is the aqueous humor, which also helps maintain ocular tension and provides essential nutrients to surrounding tissues. The aqueous fluid is constantly flowing in and out of this area in equal amounts, which helps to maintain the correct pressure. If the fluids cannot drain properly, or if excess fluids are produced, then it often results in high pressure, which is known as ocular hypertension.
Ocular hypertension is a major risk factor for glaucoma, which can eventually lead to blindness if not taken care of in time. The risk for developing ocular hypertension increases with age, but it has also been linked to genetics, eye inflammations, certain medications and other physical health problems. In addition, consumption of alcohol and caffeine as well as changes in blood pressure can negatively affect ocular tension as well. Exercise such as running, walking, yoga and Pilates, along with proper fluid intake, can help maintain ocular tension at a healthy level of 10-20 millimeters of mercury (mmHg).
If the ocular tension drops below 5 millimeters of mercury, it results in a deflated eyeball, known as ocular hypotony. This condition occurs if more fluids are drained than what the body can produce. It can occur as a result of an eye injury, dehydration, a low blood flow, inflammation or rhegmatogenous retinal detachments.
A tonometer is used to measure the pressure of the eye. There are several types, such as an applanation tonometer and a rebound tonometer. Both of these come in contact with the eye and thus require an anesthetic to be applied to the eye before the pressure can be taken. Another type of tonometer is the ocular response analyser, which does not come in contact with the eye but simply measures the shifting of the cornea as a mist of pressurized air is applied.