Measuring eye pressure: How intraocular pressure is measured during glaucoma screening

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 prevent irreversible visual impairment or blindness in an emergency.

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 increases significantly – especially in the case of a family history, short-sightedness, diabetes or high blood pressure. This is why a regular ophthalmological examination, including intraocular pressure measurement, is part of sensible glaucoma prevention, even if there are no symptoms yet.

How does an intraocular pressure measurement work?

When measuring intraocular pressure, it is determined how much pressure is exerted inside the eye on the walls of the eye and the optic nerve. This pressure is created by the aqueous humor – a clear fluid that is produced in the ciliary body behind the pupil and drained via the angle of the eye. 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 values of intraocular pressure:

The normal range is between 10 and 21 mmHg. If the measured pressure is higher than this, this may be an indication of increased eye pressure and therefore an increased risk of glaucoma.

The most important measurement methods at a glance:

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

Applanation tonometry (gold standard according to Goldmann)

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

This is how applanation tonometry works:

• The cornea is first prepared with an anesthetic eye drop.
• A fluorescent dye is applied to make the contact surface visible.
• The cornea is slightly flattened using a fine measuring probe attached to the slit lamp microscope.
• The device uses the resistance to calculate the intraocular pressure in mmHg.

Advantages:

• Very reliable and precise
• Particularly suitable for monitoring the progress of glaucoma
• Direct contact enables precise assessment with controlled fixation

The corneal thickness can influence the measurement result – therefore pachymetry(corneal thickness measurement) is often also carried out

Non-contact tonometry (air blast measurement)

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

This is how the air blast measurement works:

• The eye fixes a point of light in the device.
• A short, precisely dosed pulse of air hits the cornea.
• The sensor measures how strongly and how quickly the cornea flattens as a result of the air blast.
• The intraocular pressure (in mmHg ) is calculated from the reaction.

Advantages:

• No anesthesia necessary
• No direct contact with the eye → hygienic and comfortable
• Fast execution (range of seconds)
• Ideal for anxious patients or for glaucoma screening

Limits:

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

Rebound tonometry (e.g. iCare tonometer)

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

This is how rebound tonometry works:

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

Advantages:

• No anesthesia necessary
• Very well tolerated, even by children and sensitive eyes
• Easy to use – also ideal for self-measurement at home
• Little disturbing, as the touch is hardly noticeable

Restrictions:

• Slightly lower accuracy than with Goldmann measurement
• Not ideal for precise follow-up of 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 that was specially developed 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 of glaucoma diagnostics.

This is how Pascal tonometry works:

• The measurement is carried out using a slit lamp microscope with a special contact sensor that precisely reproduces the natural curvature of the cornea.
• After local anesthesia, the measuring device is gently placed on the cornea.
• Pressure curves in the eye are recorded continuously over several seconds.
• The device uses this to calculate the mean intraocular pressure, including the 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 for complex cases
• Additional information about the vascular supply in the eye

Disadvantages:

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

Does it hurt? What you can expect from the eye pressure measurement

No – an eye pressure measurement does not hurt. Most procedures are completely painless, some are even non-contact (e.g. air puff measurement). With contact-based methods such as Goldmann applanation or Pascal tonometry, the eye is treated with an anesthetic drop beforehand so that you don’t feel anything.

The examination usually only takes a few seconds and requires no special prior knowledge. The only important thing is not to blink and to sit still so that the result is as accurate as possible. Afterwards, you can see again immediately and continue with your everyday life.

Who pays for the measurement of high eye pressure? What does it cost?

n Austria, statutory health insurance companies only cover eye pressure measurement (tonometry) if there is a concrete medical suspicion or a known eye disease – 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 benefit.

And if there is no suspicion?

If you would like to have the measurement carried out as part of a preventive check-up without symptoms or a request for a diagnosis, it is considered an individual health service (IGeL). This means that you pay the costs yourself.

What does the eye pressure measurement cost?

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

Why increased eye pressure can lead to glaucoma:

Permanently elevated intraocular pressure is the most important risk factor for the development of glaucoma, also known as glaucoma. This leads to gradual damage to the optic nerve, which can go unnoticed for years – until the field of vision becomes noticeably restricted or even irreversible blindnessoccurs.

The reason: in a healthy eye, there is a balance between the production and outflow of aqueous humor. If this is disturbed – e.g. due to a narrowed chamber angle or delayed outflow – the pressure inside the eye increases. This mechanical pressure puts strain on the sensitive optic nerve, particularly 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, those affected do not notice any symptoms at first, as the loss of vision progresses from the outside inwards – central vision remains intact for a long time.