Why is Eye Pressure Important?

Author: Premier Eye Associates

Eye Pressure

Did you know that just like blood pressure, eye pressure can be measured within the eye?

In fact, eye pressure is a very important part of your eyes’ health! Therefore, eye pressure is checked every time you go in to see your eye doctor.


What Exactly is Eye Pressure?

The eye is an organ, it is made up of soft tissues just like any other organ in the body. In order for the eye to stay round and perfectly shaped, it is filled with fluid to keep it inflated.

There are two types of fluid in the eye, separated down the middle by a structure called the lens. The back half of the eye is filled with a jelly-like substance called vitreous humor and the front half of the eye is filled with a watery-like substance called aqueous humor.

What makes the eye unique is that the fluids (aqueous humor and vitreous humor) must be clear to allow for clear vision. Thus, this fluid is different from other parts of the body. In fact, the eye makes this fluid special for itself!

Eye pressure is technically determined by the overall fluid in the eye exerting pressure on the front surface of the eye (cornea). However, aqueous humor is what plays the major role in determining if a person’s eye pressure is high or low.


The Aqueous Humor and Eye Pressure

Aqueous humor (the fluid within the front half of the eye) is produced by filtering certain substances from the blood into the eye. It enters the eye at about the equator—right about where the lens sits.

The aqueous humor brings nutrients to the lens and cornea of the eyes to keep them healthy. Therefore it travels from the equator, to the front of the eye, and then flows out through a series of shunts and vessels where it eventually is put back into the blood.

Think about it almost like air flowing through a hot air balloon. It enters the balloon as hot air, blows it up, keeps it turgid, and then exits once it has lost its heat/ability to help push the balloon up into the sky. In the eye, however, the aqueous enters, provides nutrients, keeps the front of the eye turgid and holds it shape, and then exits at the front of the eye.

Eye pressure can become high if aqueous humor is being made and entering the eye faster than it is exiting.

Eye pressure can become low if aqueous humor is exiting the eye faster than it’s being made.

There are many different things that can cause either of these circumstances—the main one that eye doctors watch for is glaucoma.


Glaucoma and Eye Pressure

Glaucoma is a disease in which the nerve in the back of the eye—optic nerve—becomes damaged and therefore no longer transmits light detected by the eye to the brain.

There are several different types of glaucoma, so we will not get into the specifics here. However, eye pressure is a major aspect of glaucoma detection and care.

In glaucoma, high eye pressures are typically seen (again, this is not in every case, but in a majority of cases this is true). When the eye pressure is high, it pushes backwards into the back structures of the eye and compresses the optic nerve, resulting in damage to the optic nerve.

Think about the balloon again. If you put too much air into a balloon—its pressure increases until it eventually pops. The eye will NOT pop. Instead, the structures at the back of the eye get pushed on from the increased pressure and become damaged over time.

Thus, monitoring eye pressures and making sure they do not get too high is a major component of glaucoma treatment and care.

How is Eye Pressure Measured?

Eye pressure can be measured in many different ways. One of the most common methods is the dreaded air-puff test, officially called and NCT (non-contact tonometer).

The air puff test was used more commonly 10-20 years ago but is still used in some offices today.

Air is puffed at the eye at a given speed and pressure. When the air reaches the eye, it rebounds and pushes back towards the machine. The machine detects the change in speed and pressure and converts this measurement into the patient’s eye pressure.

Another method is a tool called “iCare”. This is a small handheld device with a little probe at the end. The probe comes very close to the cornea (the very front part of the eye) and bounces back into the hand-held device.

This device detects the change of speed of the probe and converts it to the patient’s eye pressure. The difference between the iCare and air puff test is that iCare takes several measurements and then averages it out to one pressure reading.

iCare devices are becoming increasingly popular as they are less invasive to the patient and relatively quick and easy, especially in today’s COVID-19 epidemic.

The golden standard of eye pressure measurement is Goldmann Tonometry. This involves a probe, eye drops, and a special blue light.

Your eye doctor will use a special microscope called a slit lamp to look at the cornea of the eye under high magnification. He or she will put a yellow-dye drop into your eye—this may stain your cornea a yellowish tint for 15-20 minutes, but will go away as your tears flush it out.

Using a blue light, your doctor will place the probe on your eye and use it to detect the pressure. This process does not hurt and tends to get the most accurate and consistent results, however it is a little more invasive than the other two methods previously listed.

There are several other methods of taking eye pressure which are also great. The three listed here are just the most commonly used—so do not be surprised if your doctor uses a different method.

What is a “Normal” Eye Pressure?

Several factors again go into determining what is normal and what is abnormal. This includes your individual thickness of your cornea, the size of your cornea, your race, medications, history of disease, family history of disease, etc.

Generally speaking, a normal reading is 10-24 mmHg. However, your eye doctor will take other characteristics into account when determining if your eye pressure is normal or abnormal.

Some people may have an eye pressure of 18 mmHg and your doctor will want to initiate the use of eye pressure depending on the other factors. Others may have an eye pressure of 26 mmHg and the doctor will opt not to do anything.

Regardless, it is always best to have your eye pressure checked every year. Having too great or too low of an eye pressure for extended periods of time can result in serious, irreversible eye damage. Make your yearly appointment to see your eye doctor today!


Dr. Anthony Spina and the staff of Premier Eye Associates specialize in glasses, soft contact lenses, hard contact lenses, and medical eye exams. Call our eye doctor in Auburn, AL today at (334) 539-5391 or schedule an appointment online  if you are interested in learning more about your eye pressure.  Our optometrist provides only the highest quality eye care services amongst eye doctors in the Auburn Alabama area.

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