Ocular Hypertension: What causes high eye pressure?

Medically reviewed by Sharon Copeland on 16 March 2021

The pressure inside the eye is also known as intraocular pressure. High eye pressure is known as ocular hypertension and can be caused by a range of factors. People with ocular hypertension are more likely to develop glaucoma.

What is ocular hypertension?

Ocular hypertension is when the pressure inside the eye is higher than usual. It can be referred to as high IOP (Intraocular Pressure).

The eye pressure builds up when the front of the eye doesn't drain the aqueous humor (fluid inside your eye) properly. The channels that normally drain the fluid from inside the eye do not function properly. More fluid is continually being produced but cannot be drained because of the improperly functioning drainage channels. This results in an increased amount of fluid inside the eye, hence raising the pressure. Most people with ocular hypertension do not experience any symptoms. For this reason, regular eye examinations with an eye doctor are very important to rule out any damage to the optic nerve from the high pressure.

High eye pressure can cause glaucoma. Ocular hypertension is not the same as glaucoma; however, those with hypertension face a higher risk of glaucoma, an eye disease which can lead to loss of vision.

What is the difference between glaucoma and ocular hypertension?

Unlike glaucoma, ocular hypertension will not cause damage to the optic nerve or vision loss. Ocular hypertension is more likely to occur than primary open-angle glaucoma, a common type of glaucoma. Glaucoma is a common eye condition where the optic nerve, which connects the eye to the brain, becomes damaged.

The term ocular hypertension usually refers to the pressure inside the eye, called intraocular pressure, being higher than normal. Eye pressure is measured in millimetres of mercury (mm Hg). Normal eye pressure ranges from 10-21 mm Hg. Ocular hypertension is an eye pressure of greater than 21 mm Hg.

What is considered dangerously high eye pressure, raised intraocular pressure and normal intraocular pressure?

Having a consistently high pressure can be a risk factor in the development of glaucoma, the higher the pressure, the greater the risk. The relationship between eye pressure and glaucoma is a complex and one which we do not fully understand, some people can have IOP and develop glaucoma some people may not, hence why it’s so important to have regular sight tests. It is essential to understand what a normal eye pressure is to gauge whether you are at risk of developing glaucoma.

Dangerously high eye pressure

An elevated IOP in people with ocular hypertension is considered dangerously high as it can cause one to develop glaucoma, resulting in optic nerve damage. People with ocular hypertension are considered glaucoma suspects.

Normal intraocular pressure

Normal intraocular pressure ranges between 10-21mm Hg.

Raised intraocular pressure

A raised intraocular pressure is anything above the measurement of 21mm Hg and is considered as ocular hypertension. Eye pressure is measured in millimetres of mercury (mm Hg).

What causes high eye pressure and how can it be reduced?

Ocular hypertension is one of the main risk factors for glaucoma. It can be caused by an imbalance in the production and drainage of fluid in the eye. When the drainage system doesn't function properly, there is an excess of fluid inside the eye, which raises the pressure in the eye. It is essential to reduce high eye pressure to prevent the risk of glaucoma.

Causes of high eye pressure

In addition to excessive fluid production and inadequate drainage, the following factors can also cause high eye pressure:

• Medications - including steroids to treat asthma
• Eye trauma
• Eye diseases
• A family history of ocular hypertension or glaucoma
• Age – chances are greater as we get older
• Ethnicity – you’re more likely to develop this condition if you are from African-Caribbean descent
• Very high myopia (short-sightedness)
• Certain medications have side effects that raise eye pressure in some people
• Eye injuries, even years after they happen, can affect your intraocular pressure

Race, family history, diabetes and age can also be a cause of high eye pressure. Those of African-Caribbean descent, those over the age of 40 and those with a family history of ocular hypertension or glaucoma, are more likely to have high eye pressure.

People who have thick corneas are often mistaken for having high eye pressure as thick corneas can cause a high reading which is often false.

Can stress raise eye pressure?

Stress can lead to an increase in blood pressure which can raise eye pressure. There is certainly a link between elevated stress levels and high eye pressure.

How can I lower my eye pressure fast?

There are several ways to lower eye pressure, including the following:

• Lower your insulin levels by avoiding sugary and carbohydrate-heavy foods
• Exercise regularly
• Reduce stress by incorporating breathing exercises, walking and yoga into your daily routine
• Eat a healthy diet full of nutrients such as vitamin C, E and A and make sure to include fatty acids and minerals
• Limit your caffeine intake
• Sleep with extra pillows to elevate your head.

These simple lifestyle changes will help to lower eye pressure; however, caring for your eyes takes time.

Can you feel ocular hypertension?

A person with ocular hypertension can usually feel the pressure behind their eyes, however it is always advised that you have regular sight tests to ensure IOP is detected.

Symptoms of ocular hypertension

It is rare to experience any symptoms with ocular hypertension and very unlikely that it will damage your vision in the short term. Nevertheless, it can lead to glaucoma, which is why it is crucial to go for regular eye tests.

Diagnosing ocular hypertension

Your eye care specialist will carry out a range of tests to check for ocular hypertension. They may look at the following:

• Your eye pressure-anything consistently above the level of 21mm Hg would indicate ocular hypertension
• Visual field testing your peripheral vision
• Other eye conditions which may be causing an increased eye pressure
• How healthy your optic nerve is

Can ocular hypertension be cured?

Ocular hypertension cannot be cured. Nevertheless, you can reduce the risk of damage to your eyes with the right treatment.

Treatment for ocular hypertension

Daily eye drops can reduce the risk of developing glaucoma. Regular eye exams are essential to monitoring eye pressure and detecting signs of glaucoma.

Does high blood pressure cause ocular hypertension?

High blood pressure can cause ocular hypertension as it causes the eye to produce more fluid and can affect the eye's drainage of that fluid. High blood pressure can also damage the retina and retinal circulation.

Does eye pressure increase with age?

Eye pressure does slowly increase with age, as does the prevalence of glaucoma. As we age, so does our eye health and people over the age of 40 are more likely to have ocular hypertension.

High eye pressure in those who are young is a cause for concern as they will face a higher risk of optic nerve damage.

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