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Early detection and treatment of glaucoma are critical for preserving your vision, but diagnosing glaucoma can be tricky. Before making a diagnosis, your ophthalmologist will likely perform a comprehensive glaucoma exam, which consists of five tests: tonometry, ophthalmoscopy, perimetry, gonioscopy, and pachymetry

Taken together, the data provided by these glaucoma tests enable your doctor to make an informed diagnosis and design a course of treatment for your unique situation. Here’s what you can expect from each of these diagnostic tests, including what each does and how each is performed.

Five types of glaucoma tests

Close-up of an older woman's eye for a glaucoma test
Your eyes will need to be dilated for your doctor to perform the necessary glaucoma tests—in order to better see the optic nerve.
(This image is from Freepik.)

Tonometry test

Tonometry measures your inner eye pressure, or intraocular pressure (IOP). 

During a tonometry test,

  1. Eye drops are used to numb the eye.
  2. Light pressure is applied to the eye with a puff of air to measure your eye’s resistance to the air hitting it.
  3. A small device, called a tonometer, is gently touched to the surface of the eye to measure the amount of pressure necessary to flatten the cornea (the clear front part of your eye).

Most tonometers are calibrated to measure IOP in millimeters of mercury (“mm Hg”). In most cases, the IOP of people with glaucoma will measure more than 20 mm Hg. Tonometry is one of the two tests used during a regular glaucoma checkup.

Ophthalmoscopy exam

Ophthalmoscopy measures the shape and color of your optic nerve. 

During an ophthalmoscopy exam,

  1. Eye drops are used to dilate (enlarge) your pupil.
  2. The doctor will use a small device with a light on it to examine the optic nerve.

Ophthalmoscopy is the second test used during a regular glaucoma checkup. If your IOP is not within the normal range and your optic nerve looks abnormal, your doctor will likely recommend the next two tests: perimetry and gonioscopy.

Perimetry test

Perimetry tests your complete field of vision—both central and peripheral (side)—for blind spots and measures the dimmest light you can see at each spot tested. 

During a perimetry test,

  1. You are asked to look straight ahead. 
  2. A light is shone at different spots in your peripheral field of vision.
  3. You press a button every time you see the light click on.

There is a certain natural blind spot in our visual field, so you may experience a delay in seeing the light as it moves around that particular spot. This is normal and does not necessarily indicate visual damage. Your doctor may recommend taking the test more than once to compare the results.

Gonioscopy exam

Gonioscopy determines whether the angle (anterior chamber) where your iris meets the back of your cornea is wide or narrow. 

During a gonioscopy exam,

  1. Eye drops are used to numb your eye.
  2. A hand-held contact lens containing a mirror is placed on your eye.

Both wide and narrow angles are potential indications of glaucoma.

Pachymetry test

Pachymetry uses an ultrasonic wave instrument to measure the thickness of your cornea. This test is painless and simple to perform, and both eyes can be measured in about a minute.

During a pachymetry test,

  1. Eye drops are used to numb the eye.
  2. The doctor places a small probe, called a pachymeter, against the surface of your eye.

Though it’s a simple procedure, pachymetry is significant. The thickness of your cornea can affect your eye pressure readings, and your corneal thickness readings help the doctor interpret your IOP readings more accurately.

How often should I get an eye exam?

Woman gets eye test at routine eye exam for glaucoma
While a normal vision test includes simple exams, like a refraction test seen here, an eye exam for glaucoma is more complex.
(This image is from Freepik.)

It’s important to keep your annual eye exams, especially if you have any of the high-risk factors for glaucoma. These risk factors include related medical conditions, such as diabetes and high blood pressure, and a family history of glaucoma.

Though people aged 60 and above are at greater risk, experts recommend getting a baseline glaucoma screening at age 40. Early signs of eye disease may begin around this time. Your eye doctor may also recommend more frequent eye exams based upon your screening results.

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