Normal eye pressure is between 10mmHg and 20mmHg. Eye pressure that’s typically associated with glaucoma is above 21mmHg, but eye damage can develop at a lower or higher pressure for some people.

A man gets his eye pressure checked with a tonometry test at the eye doctor's office. Share on Pinterest
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The front part of your eye is filled with a clear liquid called aqueous humor. This liquid gives your eye its shape and nourishes its cells. An imbalance in the amount of fluid inside your eye can lead to potentially damaging high or low eye pressure.

Doctors use a unit of measurement called millimeters of mercury (mmHg) to measure the pressure in your eyes. According to the American Academy of Ophthalmology, normal eye pressure is between 10mmHg to 20mmHg.

Changes to your eye pressure often don’t cause symptoms until the damage to the optic nerve is more advanced. However, regular eye exams can help detect pressure changes before complications develop.

In medical terms, high eye pressure is called ocular hypertension. If left untreated, it can cause damage to the optic nerve that carries information from your eye to your brain. High eye pressure is the leading cause of glaucoma.

Glaucoma is a group of conditions that cause progressive damage to your optic nerve which can lead to permanent vision loss or blindness.

Glaucoma is associated with eye pressures above 21mmHg, but the pressure at which eye damage develops is different for each person.

Low eye pressure is less common than high pressure. Sudden decreases in pressure may lead to tissue damage in the eye.

Your eye pressure can rise too high when the fluid inside your eye exerts too much pressure on the inner surface of your eye. This can occur if your eye produces too much fluid or if fluid isn’t able to drain properly.

Risk factors for developing high ocular pressure include:

  • uveitis, inflammation of the eye
  • eye trauma from injuries or surgery
  • birth defects that cause problems with eye fluid drainage
  • having a family history of high eye pressure or glaucoma
  • being over the age of 40
  • African American or Hispanic ethnicity
  • taking certain medications like long-term use of glucocorticoids
  • having pigment dispersion syndrome

Low eye pressure is usually caused by surgery to treat glaucoma. It can also be caused by:

  • reduced fluid production
  • proliferative vitreoretinopathy, a complication of retinal detachment
  • weakness of the eye due to genetic conditions such as Marfan syndrome
  • some medications like:
    • nitrates
    • antivirals such as cidofovir
    • beta-blockers

High or low eye pressure often doesn’t cause symptoms in the early stages. Regular eye exams are critical for catching changes to your eye pressure before you develop permanent eye damage.

How often do you need an eye exam?

The American Academy of Ophthalmology recommends a comprehensive eye exam:

  • every 2 to 4 years for people ages 40 to 54 who are at low risk for eye disease
  • every 1 to 3 years for people ages 55 to 64 who are at low risk for eye disease
  • every 1 to 2 years for people 65 years and older who have a low risk for eye disease
  • at least once a year for people with type 1 or type 2 diabetes, regardless of age

Any individual who has a higher risk of developing eye disease based on their medical history, family history, age, or race, may need more regular eye exams, even if they don’t have any symptoms.

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Glaucoma symptoms usually aren’t noticeable until you have some vision loss. It may start as patchy blind spots in your peripheral vision that then progresses to loss of your central vision.

Low eye pressure may cause painless vision loss and the development of blurred vision.

How is eye pressure measured?

Your eye doctor can measure the pressure in your eye with a test called tonometry. A specific type of tonometry called applanation tonometry is considered the most reliable test.

The exact procedure your eye doctor will follow can vary, but it will likely include steps similar to these:

  1. You’ll be given eye drops to numb your eyes and possibly an orange dye to temporarily stain the surface of your eye.
  2. You’ll rest your chin and forehead against supports on a machine called a slit lamp. A slit lamp is a special device that emits intense light to allow doctors to see inside your eye.
  3. The top of a device called a tonometer will be moved toward the front of your eye until it’s touching.
  4. A small amount of pressure is applied to your eye with the device. The numbing drops that you’re given will help ensure that you don’t feel any pain when this is done.

Although the procedure is painless, there’s a small chance of a scratch to the outer surface of your eye. If this happens, it usually heals by itself with no complications.

Sometimes doctors use non-contact tonometry to measure eye pressure instead. This test uses a puff of air to measure your eye pressure instead of directly contacting your eye with a tonometer.

High pressure in your eyes is treated with prescription eyedrops that either help the fluid inside your eye to drain or lower the amount you produce. These eyedrops may include one or more of the following:

  • beta-blockers such as timolol
  • prostaglandin analogs such as latanoprost
  • carbonic anhydrase inhibitors such as brinzolamide or dorzolamide
  • alpha-2 agonists such as apraclonidine
  • cholinergic agents such as pilocarpine
  • rho kinase inhibitors such as netarsudil
  • nitric oxide donors such as latanoprostene bunod

Some carbonic anhydrase inhibitors such as acetazolamide are available as oral formulas as well.

Laser treatments or glaucoma surgery may be needed if you don’t respond to medications.

Low eye pressure treatment

Low eye pressure can be treated by targeting the underlying cause, including previous surgery or injury.

Researchers are continuing to examine medications that may help increase eye pressure. Some medications under investigation have been found to increase pressure but have high levels of toxicity that make them impractical.

Your doctor may give you steroids or nonsteroidal anti-inflammatory agents to reduce inflammation.

If you have leaking fluid, your eye doctor may:

  • try patching a leak with a special contact lens
  • administer injections to improve healing
  • perform suturing
  • use viscoelastic substances to reshape the front of your eye

Normal eye pressure is considered to be between 10mmHg to 20mmHg. However, the pressure at which eye damage develops is different for each person.

High pressure inside your eye can damage your optic nerve and cause vision loss or blindness. Usually, there aren’t any symptoms until vision loss happens, which often starts in your peripheral vision. Low eye pressure is rarer but can also lead to eye damage.

Regular eye exams are the best way to detect high eye pressure before symptoms develop.