Normal Eye Pressure

The thick watery fluid called aqueous humor is present in the space between the eye lens and the cornea. The pressure generated by the fluid inside the eye is known as eye pressure or Intra-ocular Pressure (IOP). Ophthalmologists measure this pressure with the help of a tonometer. IOP helps evaluate severity of situations like glaucoma.

Role of Aqueous Humor in Eye Health
Aqueous humor provides nutrition to the eyes. It is responsible for typical convex shape of the eye (inflation of the eye). It also acts as an antioxidant. It helps prevent various eye diseases. The rate of production and drainage of aqueous humor plays an important role in maintaining normal intra-ocular pressure. Even slightly affected production or drainage of aqueous humor can lead to significant changes in the pressure. Thus, an equilibrium between the rate of production and corresponding rate of drainage of aqueous humor is essential to maintain normal eye pressure. Corneal thickness and rigidity also play an important role in measuring IOP.

Intra-ocular Pressure
The unit of measurement of eye pressure is 'millimeters of mercury' (mmHg) and normal range of IOP is 10-20 mmHg. IOP more than 20 mmHg is known as Ocular Hypertension (OHT). Average IOP is 15.5 mmHg; but it is not constant. Throughout the day and night, it may increase or decrease by about 2.75 mmHg. During daytime activities, it may increase or decrease by about 3-6 mmHg. Pressure below 12 mm Hg is referred to as low eye pressure. The condition wherein IOP is equal to, or lower than, 5 mmHg is known as ocular hypotony. Such a low IOP suggests fluid leakage and deflation of the eyeball. Both high and low eye pressure can lead to pain behind eye and headache.

Certain physical activities can affect IOP temporarily. For example, standing on your head or lifting heavy objects can affect IOP temporarily. But IOP will soon return to its original level without causing any harm. IOP varies according to heart rate, respiration, exercise and fluid intake. Certain drugs and medications also influence IOP. Caffeine leads to high IOP and alcohol abuse leads to low IOP. If high or low eye pressure continues to exist for a longer period of time, then it is considered as harmful. Proper eye care can help prevent serious eye problems. Certain exercises like walking, jogging, running, yoga and aerobics help lower intra-ocular pressure.

How is IOP Measured
Eye pressure is measured by various ways. One of the simplest way is described here. Patient is given numbing eye drops. A hand-held device, which looks like a pencil, is used by the doctor to measure IOP. The device records the pressure at once, when it touches the eye. No pain or discomfort is experienced during this procedure.

Effects of Increased IOP
The condition wherein IOP is higher than 20 mmHg, without optic nerve damage or loss of vision, is known as Ocular Hypertension. OHT is one of the most important risk factors of glaucoma. Increased intra-ocular pressure, optic nerve damage, and vision loss are noticed in patients diagnosed with glaucoma. Sometimes, differences in pressure between the two eyes is noticed; which can lead to certain types of glaucoma, iritis or retinal detachment. Certain structural problems, genetic factors, certain medications, exercises, inflammation of the eye can result in OHT. Usually, IOP increases with aging.

It is believed that psychological stress brings about changes in normal eye pressure. More studies are required to conclude about the effect of psychological stress on intr-aocular pressure. Those diagnosed with ocular hypertension are more closely watched by doctors for the onset of glaucoma. Uncontrolled glaucoma can result in loss of vision and blindness. Therefore it is necessary to consult an ophthalmologist immediately; if you have any type of eye problem.