Eye Pressure Testing
Our eyes constantly make a fluid called aqueous humor. As new aqueous flows into your eye, the same amount should drain out through a tiny drainage area. This process keeps pressure in your eye (called intraocular pressure or IOP) stable. But if the drain is not working properly, fluid builds up. Pressure inside the eye rises, damaging the optic nerve. This is often how glaucoma develops.
As part of a complete eye exam, your ophthalmologist or an assistant will measure your eye pressure. This pressure check is called tonometry.
In the past, you may have had an eye pressure test using a puff of air. Now most ophthalmologists use a more accurate device that measures pressure by direct contact with the eye.
How Is Eye Pressure Measured?
- Eye drops are put in your eyes to numb them.
- Then the doctor or assistant gently touches the front surface of your eye with a device that glows with a blue light. Other times a different handheld instrument is used.
- Both methods apply a small amount of pressure to the eye.
- This allows your ophthalmologist to measure the pressure inside each eye.
- During this test, it is very helpful to relax and breathe normally.
Each person's eye pressure is different, and there is no single correct pressure for everyone. Generally, the range for normal pressure is between 10 and 21 mmHg ("mmHg" means "millimeters of mercury," a scale used to record eye pressure).
Most people who have glaucoma will have an eye pressure higher than 21 mmHg. However, some people with pressures between 10 and 21 mmHg may have glaucoma.
Your ophthalmologist will determine the eye pressure range that is healthy specifically for you.