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Eye pressure rises mainly when the fluid circulating inside the eye does not drain properly. However, high eye pressure does not automatically mean glaucoma. Glaucoma is present only when damage to the optic nerve or the visual field is detected. If the pressure is high without any damage, the condition is called ocular hypertension.
How is pressure inside the eye regulated?
A clear fluid, the aqueous humour, is constantly produced inside the eye and nourishes the tissues of the anterior segment. This fluid drains through the angle of the eye, between the iris and the cornea, via a microscopic network that works like a filter. The balance between production and drainage determines the intraocular pressure.
In most people, the pressure ranges roughly between 10 and 21 mmHg. It is not constant throughout the 24 hours: it is often higher early in the morning and when lying down. This is why a single measurement is not always enough to draw reliable conclusions.
What raises eye pressure?
Permanent or chronic factors
- Reduced drainage with age: the filter in the angle becomes less efficient over the years.
- Narrow angle: in some eyes, often long-sighted ones, the angle is anatomically narrow and may close.
- Pseudoexfoliation and pigment dispersion: material or pigment gradually blocks the drainage system.
- Inflammation inside the eye: eye inflammation, such as uveitis, can raise the pressure.
- Trauma: an old blow to the eye can cause the pressure to rise, even years later.
Corticosteroids: a well-known and often overlooked factor
Steroid (cortisone) medicines are among the best-known causes of raised intraocular pressure. The risk is greatest with steroid eye drops, but it also exists with tablets, injections, inhalers and creams applied around the eyes. Not everyone reacts in the same way: a proportion of people are particularly sensitive, and their pressure rises within just a few weeks.
If you use steroids for a long period, in any form, let your ophthalmologist know so your eye pressure can be checked regularly. However, do not stop any medicine without speaking to the doctor who prescribed it.
Other medicines in predisposed eyes
In people with a narrow angle, certain medicines that dilate the pupil, such as some anticholinergics, antihistamines, antidepressants or anti-epileptic drugs, can rarely trigger an acute angle-closure glaucoma attack. This is why many patient information leaflets carry a glaucoma warning. Your ophthalmologist can tell you whether your angle is open or narrow.
Temporary rises in everyday life
Some situations raise the pressure briefly without causing a problem for a healthy eye. In people with advanced glaucoma, however, they deserve some care:
- head-down positions, such as certain yoga poses,
- lifting weights while holding your breath,
- intense and prolonged playing of wind instruments,
- drinking a large amount of fluid in a very short time,
- pressure on the eye, such as rubbing it or sleeping face down on the pillow.
Caffeine causes a small, temporary rise that does not appear to matter for most people. The evidence on stress is limited.
Ocular hypertension and glaucoma: what is the difference?
The two terms are very often confused. The distinction is made not only by the pressure, but by the appearance of the optic nerve and the visual field.
| Feature | Ocular hypertension | Open-angle glaucoma | Normal-tension glaucoma |
|---|---|---|---|
| Intraocular pressure | High | Usually high | Within normal limits |
| Optic nerve | Healthy | Characteristic damage | Characteristic damage |
| Visual field | Normal | Defects, often in the periphery | Defects |
| Management | Monitoring or treatment depending on risk | Treatment to lower the pressure | Treatment to lower the pressure further |
Ocular hypertension is a risk factor, not a disease. In a large American study, about one in ten patients with untreated ocular hypertension developed glaucoma within five years, while treatment significantly reduced this risk. Whether treatment is started depends on the pressure level, corneal thickness, age and the appearance of the optic nerve. Conversely, glaucoma can also occur with normal pressure readings. For a detailed look at the disease, see our page on glaucoma of the eye.
Who is at higher risk of glaucoma?
- people over 40, with the risk increasing with age,
- those with a parent or sibling with glaucoma,
- people with high myopia or, for narrow-angle glaucoma, long-sightedness (hyperopia),
- those with a thin cornea,
- people of African descent,
- those taking steroids long term,
- people with diabetes or with very low blood pressure at night.
Which tests clarify the picture?
Measuring the pressure is only the first step. For a proper assessment, the ophthalmologist combines:
- Tonometry, ideally at different times of day or at different visits.
- Pachymetry of the cornea, because a thick cornea gives falsely high readings and a thin one falsely low readings.
- Gonioscopy, to show whether the drainage angle is open or narrow.
- Examination of the optic nerve during fundoscopy.
- Optical coherence tomography, which measures the nerve fibre layer. An OCT scan detects thinning before any loss of vision appears.
- Visual fields, which record whether there are areas the eye cannot see. Find out more about visual field testing and how it is done.
How is high eye pressure treated?
When treatment is considered necessary, the aim is to lower the pressure to a level that protects the optic nerve. This level is not the same for everyone and is set individually. The main options are:
- Eye drops, which reduce the production or improve the drainage of the fluid. They need to be used daily and consistently.
- Laser, such as selective laser trabeculoplasty for open angles or iridotomy for narrow angles, both carried out in the clinic.
- Surgery, when drops and laser are not enough.
Damage that has already occurred to the optic nerve cannot be reversed. Treatment can, however, significantly slow down or stop further loss, which is why sticking to treatment and follow-up appointments is crucial.
When to see an ophthalmologist
Open-angle glaucoma is painless and causes no symptoms until a significant part of peripheral vision has been lost. This is why regular check-ups are recommended after the age of 40, and earlier or more often if you have risk factors. In contrast, an acute angle-closure attack is an emergency. Seek help immediately if you experience:
- severe eye pain and redness,
- sudden blurring of vision,
- coloured rings (halos) around lights,
- headache with nausea or vomiting together with the above.
If you have been told that you have high eye pressure, book an appointment at our clinic in Neo Psychiko, Athens, for a full glaucoma assessment.
Frequently Asked Questions about Eye Pressure
Does high blood pressure also raise eye pressure?
Blood pressure and intraocular pressure are different measurements. The link between them is small: high blood pressure is only slightly associated with higher intraocular pressure. Interestingly, very low blood pressure, especially at night, can reduce the blood supply to the optic nerve. This is why your ophthalmologist should know which medicines you take.
Can I tell on my own if I have high eye pressure?
Usually not. Raised intraocular pressure and open-angle glaucoma cause neither pain nor blurred vision in the early stages. Headaches or tired eyes are rarely due to it. The only way to know is to have your pressure measured and your optic nerve checked during an eye examination.
If I have ocular hypertension, will I definitely get glaucoma?
No. Most people with ocular hypertension do not develop glaucoma, especially when they are monitored properly. The risk is, however, increased and varies from person to person. Based on the pressure, corneal thickness, age and the optic nerve findings, the ophthalmologist decides whether monitoring is enough or treatment is needed.
Questions about your case?
Dr. Skouteris will examine you at his practice in Neo Psychiko and explain your options.
Ophthalmic surgeon trained at the John Radcliffe University Hospital in Oxford and Fellow of the European Board of Ophthalmology (FEBO).
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