Measuring eye pressure: How intraocular pressure is measured in glaucoma prevention

Excessive intraocular pressure often goes unnoticed for a long time – but can gradually damage the optic nerve and lead to the development of glaucoma. This is why regular eye pressure measurement is a key part of glaucoma prevention, especially from the age of 40 or if there are known risk factors such as short-sightedness, diabetes or a family history of the disease.

In this article, we explain how eye pressure is measured, which measurement methods are available, how reliable and painless the examination is – and when it is medically necessary. Even if you haven’t experienced any symptoms so far, you should take a closer look at this topic. After all, a simple measurement can help to keep the eye healthy in the long term – and in an emergency, prevent irreversible visual impairment or blindness.

Measuring eye pressure – when is it necessary? Symptoms of high pressure in the eye:

An eye pressure measurement is particularly important if there is a suspicion of increased intraocular pressure – as this can cause no symptoms for a long time and yet slowly damage the optic nerve. The problem only becomes noticeable when part of the vision has already been lost – which in the worst case can manifest itself as glaucoma.

• Frequent feeling of eye pressure or dull pain in the eye
• Headaches in the forehead or eye socket area
• Blurred vision or reduced vision – especially in the morning
• Halos or rings of light around light sources
• Feeling of pressure or tension when looking at screens
• Sudden deterioration in vision, with no apparent cause

From the age of 40, the risk of increased intraocular pressure rises significantly – especially with a family history, short-sightedness, diabetes or high blood pressure. Therefore, a regular ophthalmological examination including intraocular pressure measurement is part of sensible glaucoma prevention, even if no symptoms are present yet.

How does an intraocular pressure measurement work?

During intraocular pressure measurement, the amount of pressure inside the eye exerted on the walls of the eye and the optic nerve is determined. This pressure is caused by the so-called aqueous humor – a clear fluid that is produced in the ciliary body behind the pupil and drained again via the chamber angle. If there is no balance between the production and drainage of the aqueous humor, the pressure inside the eye can increase.

Intraocular pressure measurement (tonometry) determines this value in millimeters of mercury (mmHg).

Normal intraocular pressure values:

The normal range is approximately between 10 and 21 mmHg. If the measured pressure is above this, it can be an indication of increased eye pressure and thus an increased glaucoma risk.

The most important measurement methods at a glance:

In practice, intraocular pressure values are determined using the following four measurement methods.

Applanation Tonometry (Goldmann Gold Standard)

Goldmann applanation tonometry is considered the gold standard for eye pressure measurement – especially in the context of glaucoma diagnostics. It provides very precise values and is therefore particularly frequently used in ophthalmological practice. The method is based on a clear principle: the higher the intraocular pressure, the harder it is to flatten (applanate) the cornea of the eye.

How applanation tonometry works:

• The cornea is first prepared with anaesthetic eye drops.
• A fluorescent dye is applied to make the contact surface visible.
• The cornea is gently flattened using a fine measuring probe attached to the slit lamp microscope.
• Based on the resistance, the device calculates the intraocular pressure in mmHg.

Advantages:

• Very reliable and accurate
• Particularly suitable for monitoring glaucoma progression
• Direct contact allows for precise assessment with controlled fixation

The corneal thickness can influence the measurement result – therefore, pachymetry (corneal thickness measurement) is often also performed.

Non-Contact Tonometry (Air-Puff Measurement)

Non-contact tonometry, often simply referred to as air-puff measurement, is a fast, painless, and non-contact method for measuring intraocular pressure. It is particularly frequently used in preventive examinations or in initial diagnostics – e.g., in cases of suspected increased eye pressure or glaucoma.

How air-puff measurement works:

• The eye fixates on a light point in the device.
• A short, precisely dosed air pulse hits the cornea.
• The sensor measures how strongly and how quickly the cornea flattens due to the air puff.
• From the reaction, the intraocular pressure (in mmHg) is calculated.

Advantages:

• No anaesthesia necessary
• No direct contact with the eye → hygienic and comfortable
• Quick execution (seconds range)
• Ideal for anxious patients or for glaucoma prevention

Limitations:

• Slightly less accurate than applanation tonometry – especially with very thick or thin corneas
• Not ideal for monitoring glaucoma progression, but good for screenings

Rebound Tonometry (e.g., iCare Tonometer)

Rebound tonometry is a modern and particularly patient-friendly method for measuring intraocular pressure – and is often used for children, sensitive individuals, or for home glaucoma prevention. The best-known device in this class is the iCare tonometer.

How rebound tonometry works:

• A tiny, spring-loaded probe is briefly and quickly propelled against the cornea – similar to a mini-impact.
• The rebound speed provides information about how hard or soft the eye is.
• The slower the rebound, the higher the eye pressure.

Advantages:

• No anaesthesia needed
• Very well tolerated, even by children and sensitive eyes
• Easy to use – also ideal for home self-measurement
• Minimally disruptive, as the touch is barely noticeable

Limitations:

• Slightly lower accuracy than Goldmann measurement
• Not optimal for exact follow-up controls in existing glaucoma
• Corneal conditions can influence the result

Dynamic Contour Tonometry (Pascal Tonometry)

Dynamic Contour Tonometry (DCT) – also known as Pascal Tonometry – is a particularly precise measurement method developed specifically for patients with unfavorable corneal conditions. It measures intraocular pressure independently of corneal thickness and shape and is therefore considered one of the most modern methods in glaucoma diagnostics.

How Pascal tonometry works:

• The measurement is performed on the slit lamp microscope with a special contact sensor that precisely maps the natural curvature of the cornea.
• After local anaesthesia, the measuring device is gently placed on the cornea.
• Over several seconds, pressure curves in the eye are continuously recorded.
• From this, the device calculates the mean intraocular pressure, including ocular pulse amplitude (a kind of “pulse” of the eye).

Advantages:

• Independent of corneal thickness and elasticity
• Particularly reliable for patients with glaucoma or corneal changes
• Very accurate pressure profiles over time – helpful in complex cases
• Additional information about the vascular supply in the eye

Disadvantages:

• Somewhat more complex and expensive than standard procedures
• Requires local anaesthesia
• Not available in every practice

Does it hurt? What to expect during eye pressure measurement

No – an eye pressure measurement does not hurt. Most procedures are completely painless, some even non-contact (e.g., air-puff measurement). For contact-based methods such as Goldmann applanation or Pascal tonometry, the eye is pre-treated with anaesthetic drops so that you feel nothing.

The examination usually takes only a few seconds and requires no special prior knowledge. The only important thing is: do not blink and sit still so that the result is as accurate as possible. Afterwards, you can immediately see again and resume your daily routine.

Who pays for the measurement if eye pressure is too high? What does it cost?

In Austria, the statutory health insurance funds only cover eye pressure measurement (tonometry) if there is a concrete medical suspicion or a known eye condition – such as glaucoma or increased intraocular pressure. In this case, the examination is part of the medically justified diagnostics and is billed as a health insurance service.

And if there is no suspicion?

If you wish to have the measurement performed as part of a preventive examination without symptoms or a diagnostic request, it is considered an Individual Health Service (IGeL). This means: you pay the costs yourself.

What does eye pressure measurement cost?

• As part of an IGeL service: usually between 20 and 40 euros per measurement
• In a package with a glaucoma screening examination (incl. optic nerve assessment): correspondingly more

Why increased eye pressure can lead to glaucoma:

Persistently increased intraocular pressure is the most important risk factor for the development of glaucoma. This involves gradual damage to the optic nerve, which can go unnoticed for years – until the field of vision is noticeably restricted or even irreversible blindness threatens.

The reason: In a healthy eye, there is a balance between the production and drainage of aqueous humor. If this is disturbed – e.g., by a narrowed chamber angle or delayed drainage – the pressure inside the eye increases. This mechanical pressure stresses the sensitive optic nerve, especially at its entry point into the eyeball (optic disc).

The longer this pressure remains too high, the greater the risk that the nerve fibers will die. Typically: affected individuals initially notice no symptoms, as vision loss progresses from the outside in – central vision remains intact for a long time.