How to Measure Eye Pressure and What It Means for Your Eye Health

April 30, 2025

Your eyes are one of the most delicate and complex organs in your body, and keeping them healthy requires regular monitoring. One critical aspect of eye health is intraocular pressure (IOP)—the pressure inside your eye. High or unstable eye pressure can increase the risk of conditions like glaucoma, which can lead to permanent vision loss if left untreated. Understanding how eye pressure is measured and what the results mean can help you take proactive steps to protect your vision.

What Is Eye Pressure?

Eye pressure, also known as intraocular pressure (IOP), refers to the fluid pressure within the eye. The aqueous humor, a clear liquid inside the eye, helps maintain its shape and nourishes the tissues. Normally, this fluid drains out through a structure called the trabecular meshwork at the front of the eye. When the balance between fluid production and drainage is disrupted, pressure can build up, potentially leading to damage to the optic nerve—a key factor in glaucoma.


Normal eye pressure typically ranges from 10 to 21 mmHg (millimeters of mercury). When eye pressure rises above this range, it may indicate an increased risk of glaucoma or other eye conditions.

How Is Eye Pressure Measured?

Eye pressure is measured through a process called tonometry, which can be done using several different techniques. Each method provides a reliable reading of intraocular pressure and helps eye doctors assess overall eye health.

1. Goldmann Applanation Tonometry (GAT)

How It Works: This is the gold standard for measuring eye pressure. The test involves using a small probe that gently touches the cornea after numbing drops are applied. The resistance of the cornea to flattening determines the pressure inside the eye.

Why It’s Used: It provides highly accurate results and is the most widely used method for detecting glaucoma risk.

2. Non-Contact Tonometry (NCT) – "The Air Puff Test"

How It Works: This method uses a quick puff of air to slightly flatten the cornea, and a sensor calculates the pressure based on the cornea’s resistance.

Why It’s Used: It is quick and does not require eye drops, making it more comfortable for patients. However, it is generally considered less precise than Goldmann tonometry.

3. Tono-Pen (Handheld Tonometry)

How It Works: A small, pen-like device is lightly pressed against the cornea after applying numbing drops. It provides an instant pressure reading.

Why It’s Used: This method is portable and convenient, often used for children or patients who have difficulty with other tonometry tests.

4. Rebound Tonometry

How It Works: A lightweight probe makes brief contact with the cornea without the need for numbing drops. The device calculates eye pressure based on the rebound speed.

Why It’s Used: It is a quick and comfortable method that is sometimes used in home monitoring devices for glaucoma patients.

What Do Your Eye Pressure Readings Mean?

Your eye pressure measurement can provide key insights into your risk of developing glaucoma or other eye diseases.

10–21 mmHg → Normal Eye Pressure: Your eyes are within a healthy range. However, regular exams are still important to detect any changes over time.

21–30 mmHg → Elevated Eye Pressure (Ocular Hypertension): Higher than normal pressure may indicate a risk of glaucoma, even if no vision loss has occurred. Your doctor may monitor your eyes closely or recommend treatment.

Above 30 mmHg → High-Risk Pressure: This level of pressure significantly increases the likelihood of optic nerve damage and requires immediate medical attention.

Below 10 mmHg → Low Eye Pressure (Hypotony): While less common, abnormally low pressure can indicate issues such as leaking fluid or retinal detachment.

Why Is Measuring Eye Pressure Important?

Regular eye pressure checks are essential for detecting early signs of glaucoma, a leading cause of irreversible blindness. Since glaucoma often develops without noticeable symptoms, many people don’t realize they have the disease until permanent vision loss occurs. In addition to glaucoma, abnormal eye pressure can be linked to:

Ocular Hypertension – Increased pressure without optic nerve damage (but still a glaucoma risk factor).

Inflammatory Eye Conditions (Uveitis) – Can cause fluctuations in eye pressure.

Eye Injuries – Trauma to the eye can lead to either high or low eye pressure.

Cataract Surgery or Other Procedures – Some eye surgeries can temporarily affect intraocular pressure.

Schedule an Eye Pressure Check Today

Monitoring your eye pressure is a simple but critical step in preserving your eyesight. If it’s been a while since your last eye exam or if you have risk factors for glaucoma, now is the time to schedule a comprehensive eye check. At Harvey & Lewis Opticians, our professional eye doctors use advanced technology, including Visual Field and OCT testing, to assess your eye health and detect any early signs of disease. With multiple convenient locations across Connecticut, we make it easy to prioritize your vision care. Don’t wait—schedule your eye exam today by calling your nearest Harvey & Lewis location to book an appointment. Your eyes deserve the best care!