Pachymetry Test

What is a pachymetry test?

A pachymetry test, or corneal pachymetry test, measures the thickness of your cornea. The cornea is the clear, tough tissue in your eye that helps you focus and offers protection by keeping out dirt and germs.

There’s a link between corneal pachymetry and corneal topography. Corneal topography creates color-coded maps of your cornea.

When is a pachymetry test performed?

Your eye care provider may measure your cornea’s thickness when diagnosing or treating:

• Glaucoma.
• Refractive errors. Your provider will want to measure your cornea if you’re having corrective surgery like LASIK.
• Corneal diseases like corneal hydrops, keratoconus and Fuchs’ dystrophy.
• Eye injuries.

A pachymetry test will help your eye care provider make sense of your tonometry test, which measures intraocular pressure (IOP).

How does a pachymetry test work?

There are two different pachymetry tests, including optical and ultrasonic (ultrasound). You don’t need to prepare for this type of test. The equipment generally takes a series of measurements and provides the average as your result.

Optical pachymetry

Your provider may use imaging systems to do an optical pachymetry test, including optical coherence tomography.

In optical pachymetry, you’ll sit down in front of the equipment. You’ll put your head and chin up against a machine that will take the measurements from images. The pachymetry equipment doesn’t touch your eye.

Ultrasonic pachymetry

• Your provider will put numbing drops into your eye.
• They’ll use a sterilized handheld pachymeter to touch your cornea for only a few seconds.
• They’ll measure the central part of your cornea and may measure other areas of your cornea as well. The test uses ultrasound waves to measure thickness.

You may want to have a driver if you know you’re having any kind of eye drops at an eye exam. Sometimes, eye drops can make your pupils open very wide (dilate). It could be difficult to see. Numbing eye drops may also affect your vision.

What are the risks of pachymetry?

There aren’t risks associated with optical pachymetry. The risks associated with ultrasonic pachymetry are few, but they can include:

• Infection.
• Eye irritation.
• Issues with numbing eye drops.
• Temporary damage to the cornea from the contact with the pachymeter.

If you have any difficulty with your vision after any type of eye exam, contact your eye care provider.

What type of results do you get from pachymetry?

Your provider will have the results of the measurements right away. They should be able to discuss them with you at this time.

In the U.S., the range of typical central cornea thickness (CCT) values is between 540 and 550 micrometers (or microns). However, these figures are estimates. Your provider will consider other factors in determining what the results mean, including your age and health. Your eyes can still be healthy if the thickness values fall outside of the typical range.

If the results of a pachymetry test are abnormal, what are the next steps?

Your provider will use the pachymetry test results to consider the next steps in treating glaucoma or will use the information to evaluate you for eye surgery. Your surgeon will want to make sure your cornea is thick enough, reducing the risk of corneal ectasia, which happens when your cornea bulges forward.

What does having a thick cornea mean?

Having a thicker cornea could mean that you’re less likely to have glaucoma. People with thicker corneas can also look like they have higher eye pressure than they really do. Knowing the thickness of your cornea will help your provider diagnose you correctly.