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Intraocular Pressure (IOP): What It Is, Normal Range and High Eye Pressure
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Intraocular pressure (IOP) (noun, abbreviated IOP; also called eye pressure): the pressure of the fluid inside the eye, measured in millimetres of mercury (mmHg). A normal intraocular pressure is roughly 10 to 21 mmHg and changes through the day. Pressure that is too high for your optic nerve can damage the nerve and lead to glaucoma, which is why glaucoma care at Laser Istanbul Clinic, led by Prof. Dr. Ahmet Satıcı, centres on lowering it.
Intraocular pressure: key facts
- What it is
- The fluid pressure inside the eye, which keeps the eye in shape
- Unit
- Millimetres of mercury (mmHg)
- Normal range
- About 10 to 21 mmHg (some sources give 10 to 20); it varies through the day and from person to person
- What makes it
- A clear fluid, the aqueous humour, made just behind the iris and drained where the iris meets the cornea
- High IOP without nerve damage
- Called ocular hypertension; the optic nerve looks normal and vision is not affected
- Link with glaucoma
- Pressure is the risk factor that treatment can change, but glaucoma also occurs at normal pressure
- Symptoms
- Usually none; a sudden, very high pressure (angle-closure attack) causes severe pain and is an emergency
- Measured by
- Tonometry: a quick test, usually by air puff or a gentle touch after numbing drops
- Specialist
- Ophthalmologist; at Laser Istanbul Clinic, glaucoma is treated by Prof. Dr. Ahmet Satıcı
What is intraocular pressure?
Intraocular pressure is the pressure of the fluid inside your eye. The front part of the eye, between the iris (the coloured part) and the cornea, is filled with a clear fluid called the aqueous humour. The American Academy of Ophthalmology (AAO) explains that this fluid is made just behind the iris, circulates through the front of the eye and then drains out where the iris meets the cornea. As long as the fluid is made and drained in balance, the pressure stays steady and the eye keeps its shape.
You can think of it like a tap and a drain. If the drain works well, the pressure stays in its normal range. If the drain is partly blocked, fluid builds up and the pressure rises. The NHS describes glaucoma in the same way: it usually results from fluid building up in the eye because it cannot drain properly, which can damage the optic nerve that connects the eye to the brain.
Eye pressure is not the same thing as blood pressure. Having diabetes or high blood pressure is, however, listed among the risk factors for raised eye pressure.
What is a normal eye pressure?
A normal eye pressure is about 10 to 21 mmHg, according to the AAO. Another AAO page rounds this to 10 to 20 mmHg, so you will see both figures. The number changes during the day, which is why a single reading is only a snapshot.
The important point is that "normal" is not exactly the same for everyone. The US National Eye Institute (NEI) notes that normal eye pressure varies by person, so what is normal for one person could be high for another. Some people with pressure above the usual range never develop glaucoma, and some people develop glaucoma with pressure inside the usual range.
| Eye pressure situation | What it means | What usually happens |
|---|---|---|
| About 10 to 21 mmHg, healthy optic nerve | Within the usual range | Routine checks |
| Higher than normal, healthy optic nerve and normal vision | Ocular hypertension (a "glaucoma suspect") | Monitoring, sometimes eye drops |
| Higher than normal, optic nerve damage and loss of side vision | Glaucoma with raised pressure | Treatment to lower the pressure |
| Within the usual range, optic nerve damage and loss of side vision | Normal-tension glaucoma | Treatment to lower the pressure further |
What causes high intraocular pressure?
High intraocular pressure is usually the result of fluid that does not drain well enough through the eye's drainage angle. The AAO lists these risk factors for ocular hypertension:
- A family history of ocular hypertension or glaucoma
- Diabetes or high blood pressure
- Age over 40
- African-American or Hispanic ethnicity
- Severe short-sightedness (myopia)
- Long-term steroid use
- A past eye injury or eye surgery
- Pigment dispersion syndrome or pseudoexfoliation syndrome (two conditions that affect the eye's drainage system)
Steroids and eye pressure
Corticosteroids can raise eye pressure in some people. EyeWiki, the AAO's clinical wiki, reports that steroid eye drops usually raise the pressure within 3 to 6 weeks and that about 1 to 4 in 100 people show a significant rise with drops. Steroid injections into or around the eye carry a higher chance: roughly half of people have a rise after an intravitreal triamcinolone injection. Steroids taken by mouth, inhaled, or applied to the eyelid skin can also do it in susceptible people. When the steroid is stopped, the pressure usually returns to normal within days to weeks, but never stop a prescribed steroid on your own; ask the doctor who prescribed it. Tell every eye doctor about all steroid treatment you use.
Injury, surgery and narrow angles
Eye injuries and eye surgery are also listed risk factors. In eyes with a narrow drainage angle, the angle can close suddenly, which causes the emergency described below.
Does high eye pressure mean glaucoma?
No. High eye pressure does not always mean glaucoma. Ocular hypertension means the intraocular pressure is higher than normal while the optic nerve looks normal and there is no vision loss, according to the AAO. People in this group are called "glaucoma suspects" because they have a higher chance of developing glaucoma later.
The cut-off varies by source. The AAO describes damaging pressure as typically above 21 mmHg, while EyeWiki defines ocular hypertension as an IOP of 24 mmHg or more with a normal optic nerve, normal visual fields and open drainage angles. Your ophthalmologist decides what is high for you by looking at the whole picture, not the number alone.
How likely is ocular hypertension to become glaucoma?
The Ocular Hypertension Treatment Study, summarised on EyeWiki, found that about 9.5% of untreated people with raised pressure developed primary open-angle glaucoma within 5 years, compared with 4.4% of those treated with eye drops, a relative risk reduction of roughly 60%. Over around 20 years of follow-up about 45% eventually developed glaucoma, usually later and with mild disease. The same summary lists the strongest warning signs: a central corneal thickness below 555 micrometres, a baseline IOP above 24 mmHg, a larger cup-to-disc ratio of the optic nerve, and older age. This is why your doctor measures your corneal thickness and examines your optic nerve instead of treating the pressure number by itself.
Normal-tension glaucoma
Normal-tension glaucoma is glaucoma with eye pressure that stays at or below 21 mmHg. In the Collaborative Normal-Tension Glaucoma Study, summarised on EyeWiki, lowering the pressure by 30% reduced the risk of progression: 12% of treated eyes progressed at five years against 35% of untreated eyes. So even when the pressure is "normal", lowering it can protect the nerve.
Glossary: Glaucoma
What are the symptoms of high eye pressure?
Usually there are none. Raised pressure and early open-angle glaucoma do not hurt and do not blur your vision, which is why the AAO calls glaucoma the "silent thief of sight". Blind spots appear slowly in the side (peripheral) vision, and most people do not notice them until the damage is advanced. The NHS also says glaucoma is usually found during a routine eye test, often before it causes any symptoms.
This is the single most important fact about eye pressure: you cannot feel it, so you can only find out by having it measured.
The emergency: acute angle-closure glaucoma
When the drainage angle closes suddenly, the pressure rises very quickly. The symptoms are:
- Severe eye pain
- A red eye
- Blurred vision
- Rainbow-coloured rings or halos around lights
- Headache
- Nausea or vomiting
This is a true eye emergency. The AAO advises calling your ophthalmologist right away, and the NHS says to call 999 or go to A&E if symptoms develop suddenly. Outside the UK, go to the nearest emergency department. Without prompt treatment an attack can lead to blindness.
How is intraocular pressure measured?
Eye pressure is measured with a quick test called tonometry. It is part of a comprehensive eye examination, and the NEI says it does not hurt. The usual methods are:
- Air-puff test: you rest your chin on a machine, and it blows a quick puff of air onto the eye. It is a painless screening test.
- Applanation tonometry: after numbing drops, the specialist gently presses a small probe on the surface of the cornea, either through the slit-lamp microscope or with a handheld device.
Why one reading is not enough
The AAO is clear that a single eye-pressure test by itself is not enough to diagnose glaucoma. Pressure changes through the day, and corneal thickness helps doctors interpret a raised reading. A glaucoma examination therefore adds:
- Pachymetry: measures the thickness of the cornea. People with thin corneas are at higher risk of glaucoma.
- Gonioscopy: a special mirrored contact lens to see whether the drainage angle is open or closed.
- Optic nerve examination and imaging: to look for damage to the nerve.
- Visual field test: to check your side vision for blind spots.
How is high eye pressure treated?
High eye pressure is treated by lowering it, because that slows or prevents optic nerve damage. The AAO is also clear about the limit: glaucoma damage is permanent and cannot be reversed, so treatment aims to stop further damage. The NHS adds that there is no cure, but treatment can slow the damage.
| Treatment | How it lowers pressure | Notes |
|---|---|---|
| Eye drops | Reduce the amount of fluid the eye makes, or help it drain | The usual first approach; prostaglandin analogues are a common first-line choice. Side effects can include stinging, itching, red eyes, blurred vision, and eyelash growth or changes in the look of the eye |
| Laser trabeculoplasty (SLT) | Makes the drainage angle work better in open-angle glaucoma | A laser treatment |
| Laser iridotomy | Makes a tiny hole in the iris so fluid can flow, used in angle-closure glaucoma | A laser treatment |
| Trabeculectomy | Creates a small flap in the sclera and a pocket (bleb) for fluid to drain | Operating-theatre surgery |
| Drainage devices (tube shunts) | A tiny tube carries fluid to a reservoir under the conjunctiva | Operating-theatre surgery |
| Cataract surgery | Removing the natural lens can lower pressure by opening space between the iris and cornea | Particularly helpful in narrow-angle eyes |
Treatment only works if you keep using it. The AAO notes that people with glaucoma need regular ophthalmology visits, every 3 to 6 months, and consistent use of their medication.
Can you lower eye pressure at home?
None of the sources we checked describes a home remedy that replaces eye drops, laser or surgery. What you can do is have your pressure measured, use your prescribed drops exactly as directed, tell your doctor about any steroid use, and keep every follow-up appointment.
Treatment with us
At Laser Istanbul Clinic, glaucoma care is led by Prof. Dr. Ahmet Satıcı, who treats glaucoma from SLT laser through trabeculectomy to MIGS stents. Surgery takes place in a fully equipped, Ministry of Health–licensed operating theatre in Istanbul. Your pre-operative examination and scans, surgery by the named surgeon, medication, follow-up checks in Istanbul, a personal interpreter, a coordinator and remote follow-up are included in the price we quote you in writing. Hotel and airport transfers are not included; we arrange them on request at a separate charge.
Glaucoma treatment & surgery in TurkeyWhen to see a doctor about your eye pressure
See an eye doctor and have your pressure measured if any of these apply:
- You are over 40 and have never had a full eye examination with a pressure check. The NHS recommends an eye test at least every two years, and the NEI suggests every 1 to 2 years for people at higher risk.
- You have a family history of glaucoma, or you have diabetes, high blood pressure or severe short-sightedness.
- You use steroid eye drops, injections, or long-term steroids by mouth or inhaler.
- You have had an eye injury or eye surgery.
- You have been told your pressure is "borderline" or you are a "glaucoma suspect" and have not had a follow-up.
- You notice blind spots or a narrowing of your side vision.
Go to an emergency department immediately if you have sudden severe eye pain, a red eye, halos around lights, blurred vision, headache, or nausea and vomiting.
Not sure what your reports mean? Send them to us, and our team will tell you what they show and which treatment, if any, may suit you.
Frequently asked questions
Intraocular pressure is the fluid pressure inside the eye, measured in millimetres of mercury (mmHg). The fluid, called aqueous humour, is made behind the iris and drains where the iris meets the cornea. When production and drainage are in balance, the pressure stays steady and the eye keeps its shape.
A normal intraocular pressure is about 10 to 21 mmHg, according to the AAO, and some pages quote 10 to 20 mmHg. It changes during the day and varies from person to person. A reading in this range does not by itself rule out glaucoma, and a higher reading does not by itself prove it.
There is no single number that is dangerous for everyone. Pressure above about 21 mmHg is generally considered high, and the risk of nerve damage rises with higher pressure, thin corneas, older age and other risk factors. A very sudden, very high pressure with severe pain, a red eye and nausea is an emergency, whatever the number.
No. If your pressure is high but your optic nerve looks normal and your vision is normal, you have ocular hypertension, not glaucoma. In the Ocular Hypertension Treatment Study, about 9.5% of untreated people developed glaucoma within 5 years, so most did not in that time, but you do need monitoring.
Usually not. Raised pressure and early glaucoma are painless, and vision loss starts in the side vision, so most people notice nothing. Only a sudden angle-closure attack causes pain, redness, halos and nausea. The only reliable way to know your pressure is to have it measured.
Usually the eye's drainage system does not let the fluid out fast enough. Risk factors include family history, diabetes, high blood pressure, age over 40, severe short-sightedness, previous eye injury or surgery, pigment dispersion or pseudoexfoliation, and the use of steroids (eye drops, injections, tablets or inhalers).
With tonometry, a quick test that is part of an eye examination. Either a puff of air is blown onto the eye, or a small probe gently touches the cornea after numbing drops. Because one reading is not enough, a diagnosis also uses pachymetry, an optic nerve examination and a visual field test.
Treatment lowers pressure with prescription eye drops, laser (trabeculoplasty or iridotomy) or surgery (trabeculectomy, drainage devices, and cataract surgery in some narrow-angle eyes). Which one suits you depends on the cause and on your optic nerve. Use any prescribed drops as directed and do not stop them without asking your doctor.
Yes. Normal-tension glaucoma is glaucoma with an eye pressure at or below 21 mmHg. It is treated by lowering the pressure further: in one large study, with a 30% reduction, 12% of treated eyes progressed at five years against 35% of untreated eyes.
Sources for the facts on this page
- American Academy of Ophthalmology. Eye Pressure and Glaucoma. https://www.aao.org/eye-health/tips-prevention/eye-pressure-glaucoma
- American Academy of Ophthalmology. What Is Glaucoma? https://www.aao.org/eye-health/diseases/what-is-glaucoma
- American Academy of Ophthalmology. What Is Ocular Hypertension? https://www.aao.org/eye-health/diseases/what-is-ocular-hypertension
- American Academy of Ophthalmology. Glaucoma Diagnosis. https://www.aao.org/eye-health/diseases/glaucoma-diagnosis
- American Academy of Ophthalmology. Glaucoma Symptoms. https://www.aao.org/eye-health/diseases/glaucoma-symptoms
- American Academy of Ophthalmology. Glaucoma Treatment. https://www.aao.org/eye-health/treatments/glaucoma-treatment
- National Eye Institute (NIH). Glaucoma. https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/glaucoma
- National Eye Institute (NIH). Get a Dilated Eye Exam. https://www.nei.nih.gov/learn-about-eye-health/healthy-vision/get-dilated-eye-exam
- MedlinePlus (NIH). Glaucoma Tests. https://medlineplus.gov/lab-tests/glaucoma-tests/
- NHS. Glaucoma. https://www.nhs.uk/conditions/glaucoma/
- NHS. Glaucoma: diagnosis. https://www.nhs.uk/conditions/glaucoma/diagnosis/
- EyeWiki (AAO). Ocular Hypertension (includes a summary of the Ocular Hypertension Treatment Study). https://eyewiki.org/Ocular_Hypertension
- EyeWiki (AAO). Normal Tension Glaucoma (includes a summary of the Collaborative Normal-Tension Glaucoma Study). https://eyewiki.org/Normal_Tension_Glaucoma
- EyeWiki (AAO). Steroid-Induced Glaucoma. https://eyewiki.org/Steroid-Induced_Glaucoma
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