What is normal eye pressure?

What is eye pressure, and how is it measured?

Like everything else in our bodies, the eyes need to stay in balance to be healthy. Normal eye pressure helps the cavity inside the eyes keep its shape and ensures good circulation of nutrients to the cornea and lens.

But when the fluids in your eyes aren't circulating properly, that pressure imbalance can cause some serious and hard-to-detect problems. When the pressure in these areas builds up too high, or dips too low, the result can even be a temporary or permanent loss of vision. 

Eye pressure explained

Your eyes are soft and full of fluids. One fluid, the old-timey sounding aqueous humor, fills the space in the front of the eye between the lens and the cornea. Blood vessels can't grow here because they'd block your vision, so instead, the transparent aqueous humor circulates oxygen and nutrients in this small space. Behind the lens, the eye has a large cavity that also has fluid in it. This is the vitreous humor, which is more jelly-like and helps the eye keep its shape by applying stable pressure to the cavity.

If everything is going right, both of these fluids continuously circulate through their cavities, carrying nutrients in and removing waste the way blood does for other parts of the body.

But when things aren't right, one or both of the fluids can get trapped and build up, causing an increase in pressure. This can cause several problems, up to and including blindness if the pressure damages the optic nerve.

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Measuring eye pressure

The most common way to measure eye pressure is called tonometry. These three tests measure the pressure inside your eye by gently pressing against your corneas, and measuring how much force it takes to push them in.

Imagine pressing your finger into a water balloon until it deforms a bit. If the balloon is very full, the pressure inside is high, and it takes more force to push in the walls. If the pressure is low, it's easier to press the balloon flat. Please note: don’t stick your fingers in your eyes, okay?

The most common tonometry test is probably the “puff” test, or the non-contact tonometry test. This uses a puff of compressed air to push the cornea, so your eye care professional doesn't have to physically make contact with the front of your eye.

While this isn't the most accurate way to do the test, it does give a good ballpark figure for people with normal eye pressure. It's quick and kid-friendly, so it's preferred for pediatric eye exams.

If your non-contact test came up with higher than expected pressure, or if you're in a high-risk group for glaucoma, you might get applanation, sometimes called a Goldmann tonometry.

For this test, the provider puts numbing drops in your eyes so you don't feel the probe, which then gently presses against the front of the cornea. Your eyes are then examined through a slit lamp for a precise pressure reading. This is a more accurate test than the no-contact one, and it's usually done as a follow-up to get precise readings for at-risk individuals.

Finally, electronic indentation tonometry involves the tester putting a small electronic device on the cornea. The instrument tests the pressure in your eyes with painless electrical signals, like radar pulses for your eyes. The feedback comes up on a computer monitor nearby and generates immediate results.

Who needs tonometry?

Your eye care professional might recommend one or another type of tonometry test for several reasons. A test for normal eye pressure could just be a regular part of your eye exam, or it could be a special order for these risk factors:

• A high pressure reading
• Family history of glaucoma
• Being over age 40
• Elevated-risk racial group
• History of eye injuries
• High blood pressure or diabetes
• Migraines
• Unusually thin corneas
• Blurred or tunnel vision
• Eye pain
• Seeing halos around lights
• Losing peripheral vision

What is considered normal eye pressure?

Normal eye pressure can be a bit different from person to person, but yours should fall within a stable range. Certain factors can drive pressure out of balance and cause or signal the presence of a medical condition.

What is the average eye pressure range?

Eye pressure is measured in millimeters of mercury (mmHg). Normal eye pressure for most adults is between 10 and 20 mmHg. But what really matters is the comparison between one reading and another. While there's usually some variation within the normal eye pressure range, and some variation is normal, results above 20 mmHg are a warning sign.

Factors affecting eye pressure

Pressure that builds up behind the eyes can cause a lot of pain, but interestingly, this usually isn’t a sign of trouble in the aqueous or vitreous humors. High fluid pressure inside the eye is usually painless, unless it's gotten to extreme levels.

Rather, painful pressure is much more likely to result from an infection behind the orbits, or eye sockets. This can be caused by a lot of things, including a persistent toothache, so it's always worth getting checked out.

The importance of monitoring eye pressure

Eye pressure can be a helpful window into the state of your health. The main pressure-related eye condition is glaucoma, but several other conditions are either caused by or associated with abnormal eye pressure.

Since pain isn’t a normal symptom of glaucoma, it’s all the more important to get regular eye exams, because this is the only reliable way to detect high pressure inside the eye.

The relationship between eye pressure and glaucoma

Glaucoma is a medical condition caused by excess pressure inside the eyes. When the pressure builds up high enough and stays there long enough, damage can be done to the optic nerves that feed visual data back to the brain.

Pinching these nerves affects vision the same way your arm can go to sleep if you lie on it wrong. If it happens once or twice, you may not have a problem, but consistently high pressure can easily cause vision loss, up to and including total blindness.

If regular eye exams have caught the glaucoma before it goes on too long, the pressure can be brought down in most cases, and severe damage avoided. Delays in treatment may cause partial vision loss or temporary total blindness.

Eventually, untreated glaucoma can take your vision for good by causing permanent and untreatable damage, making it impossible for your eyes to communicate with your brain. After cataracts, this is the second-leading cause of blindness, affecting nearly 58 million people worldwide.

Eye pressure's role in other medical conditions

Glaucoma isn't the only medical problem that's connected with eye pressure. Ocular hypertension is a precursor to glaucoma, and it refers to the buildup of pressure in the eye by itself. Even if your optic nerve is fine, this hypertension can cause thinning of the cornea and a variety of other eye conditions over time. Some of these badly affect the way you see, such as causing blurred vision, and many can only be found during an eye exam.

When to seek medical attention

You should be getting an eye exam every year, especially if you're over 40 or have relatives with eye problems, including poor vision. Apart from that, there are a few reasons to schedule an eye exam without delay. These include:

• When your regular doctor advises an eye exam
• When you're starting a new job, such as ambulance driver or heavy equipment operator, that requires healthy vision
• When you have severe or persistent eye pain
• If your eyes start to look odd, such as being consistently red or brown, dry, ulcerated, or otherwise not normal
• After you suffer an injury, no matter how minor, to the eye area
• If you've been having vision disturbances, especially tunnel vision or wavy lines around your line of sight
• A noticeable loss of vision acuity, such as being unable to read close up or see things clearly in the distance

Normal eye pressure is a big deal

You might not be in the habit of wondering how your eye pressure is doing, but it's more important to your health than many people think. Getting regular eye exams and monitoring for normal eye pressure is just another part of your regular medical checkup routine.

Even if you get nothing but normal eye pressure readings all your life, it’s worthwhile to have peace of mind that glaucoma isn't a problem for you, and that your vision is doing okay.

If you've never had a proper check for eye pressure before, or if it's been a while, book an eye exam in your area today, and make sure all is well with your eyes.

FAQs

Can eye pressure change throughout the day?

Like many things in the body, your eye pressure can change a bit during the day as fluid flows in and out. But it should stay within the normal (10 and 20 mmHg) eye pressure range.

How often should you have your eye pressure checked?

Adding an eye pressure check to your annual health care routine is a good idea. Your eye care professional may recommend more frequent checks if you're in a higher-risk category.

Can normal eye pressure prevent glaucoma?

Normal eye pressure helps prevent glaucoma, but it's not 100% guaranteed. Some people, especially those in high-risk groups, still get glaucoma without ocular hypertension.