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What is normal eye pressure, and what does a high reading mean?

When people hear "eye pressure" they often think of blood pressure. The two are different. Eye pressure is the pressure of the fluid inside the eye, and it is one of the most important numbers in an eye check-up, because raised eye pressure is the main risk factor for glaucoma. This guide explains what the numbers mean. For glaucoma care at ReNew Vision, see glaucoma check-up and treatment in Vasco.

What is eye pressure?

The front part of the eye is filled with a clear, watery fluid that nourishes the lens and the cornea. It is made continuously and drains out through a fine mesh in the angle where the iris meets the cornea. The balance between how much fluid is made and how fast it drains sets the pressure inside the eye, which keeps the eye firm and its shape steady. If drainage slows, the pressure rises, and over time high pressure can damage the optic nerve.

Eye pressure is measured in millimetres of mercury (mmHg), the same unit as blood pressure, but the two are not linked in a simple way. Having high blood pressure does not mean you have high eye pressure.

What is a normal eye pressure?

In most people, eye pressure is between about 10 and 21 mmHg. But "normal" is a range on a population, not a safe line for each person:

• some people have glaucoma damage with pressure inside this range
• some people have pressure above it for years with no damage
• pressure changes through the day, and is often higher in the early morning
• the two eyes can read differently
• the thickness of the cornea can make the reading seem higher or lower than the true pressure

So one reading is never the whole story. The eye doctor looks at the pressure together with the optic nerve, the drainage angle, your family history and, when needed, a visual field test.

What does a high eye pressure reading mean?

It means the eye needs a closer look. There are three common answers:

• Ocular hypertension: the pressure is above the usual range, but the optic nerve and side vision are healthy. Some people with ocular hypertension develop glaucoma over the years and many do not. The eye doctor decides whether to treat or to watch, depending on how high the pressure is and your other risks.
• Glaucoma: raised pressure with signs of damage to the optic nerve. Treatment lowers the pressure to protect the sight you have.
• A one-off reading: pressure can read high if you squeezed your eyes shut, held your breath, or wore a tight collar during the test. A repeat measurement settles it.

Can I have glaucoma with normal eye pressure?

Yes. In normal-pressure (normal-tension) glaucoma, the optic nerve is damaged although the pressure stays within the usual range. The nerve in these eyes seems more sensitive to pressure, and blood flow to the nerve may play a part. Treatment still aims to lower the pressure, below the person's own starting level. This is the main reason a glaucoma check never relies on the pressure alone.

What causes high eye pressure?

• slow drainage through the mesh in the drainage angle, the usual cause in open-angle glaucoma
• a narrow drainage angle that the iris can block, in angle-closure glaucoma
• steroid medicines, especially steroid eye drops used for weeks without an eye doctor checking the pressure
• an old eye injury, or inflammation inside the eye
• advanced diabetic eye disease

A word of caution: steroid eye drops are sometimes bought over the counter for red or itchy eyes. Never use them unless an eye doctor has prescribed them and is checking your eye pressure.

Does high eye pressure cause symptoms?

Usually not. Pressure that rises slowly does not hurt, redden the eye or blur vision, which is why it is only found by measuring it. The exception is a sudden, very high rise in an angle-closure attack: severe eye pain, a red eye, blurred vision, haloes around lights, headache and vomiting. That is an emergency; emergency eye care at ReNew Vision is available 24 hours. See eye emergency.

How is the eye pressure test done?

The test is called tonometry and takes only a few seconds for each eye. Depending on the instrument and your eye, it is done in one of these ways:

• A puff of air blown briefly at the eye. It makes you blink; most people feel only the brief puff.
• A light touch of a small measuring tip on the eye, after a numbing drop and sometimes a yellow dye. Most people feel no more than a faint touch.
• A handheld device with a tiny tip that touches the eye very briefly.

To get an accurate reading: sit comfortably, breathe normally rather than holding your breath, keep both eyes open and look where you are asked. After a numbing drop, do not rub your eyes until the numbness has worn off. If you use glaucoma drops, keep using them as usual before the test, and tell the eye doctor what time you last put them in.

Can I lower my eye pressure naturally?

Healthy habits are good for you, but no diet, exercise or home remedy can replace glaucoma treatment. Some practical points:

• Regular moderate exercise, such as walking, is fine and may lower the pressure a little.
• Head-down positions, such as some yoga poses, raise eye pressure while you hold them. If you have glaucoma, ask the eye doctor about them.
• Large amounts of strong coffee or tea at one time can raise the pressure slightly; normal amounts are fine for most people.
• Never stop or skip prescribed glaucoma drops because you feel well.

How often should my eye pressure be checked?

As part of every complete eye check-up from about 40, and more often if you have glaucoma, ocular hypertension, a narrow angle, a family history of glaucoma or long-term steroid use. People on glaucoma treatment usually have their pressure checked every few months. For family risk, see is glaucoma hereditary? For the symptoms of glaucoma, see why glaucoma is called silent.

Eye pressure tests in Vasco

The eye pressure test is part of every complete eye check-up at ReNew Vision Eye Hospital, Vaddem, Vasco da Gama; see eye check-up in Vasco. Eye OPD Monday to Saturday, 4 pm to 7 pm. Call or WhatsApp 072489 88039.

Questions patients ask

What is a normal eye pressure?

In most people it is between about 10 and 21 mmHg. But glaucoma can occur within this range and some people stay healthy above it, so the eye doctor judges the pressure together with the optic nerve and drainage angle.

Is high eye pressure the same as glaucoma?

No. High pressure with a healthy optic nerve is called ocular hypertension; it raises the risk of glaucoma but does not always lead to it. Glaucoma means the optic nerve shows damage.

Does high eye pressure cause headaches?

Usually not. Slowly rising pressure gives no symptoms. A sudden very high rise in an angle-closure attack causes severe eye pain, headache, a red eye, blurred vision and vomiting, which is an emergency.

Does the eye pressure test hurt?

Most people feel very little. It takes a few seconds: a brief puff of air, or a faint touch after a numbing drop. Do not rub your eyes until a numbing drop has worn off.

Should I use my glaucoma drops before an eye pressure check?

Yes, keep using them as usual unless the eye doctor has told you otherwise, and note the time of your last drop. This shows how well the treatment is working.

This page is general eye-health information, not personal medical advice. Your eye doctor advises you after examining your eyes.