What tests are involved in determining glaucoma? “YouTube Eye Doctor” Michael Nelson, O.D., FAAO, a Canadian optometrist practicing in Winnipeg, educates patients on a full spectrum of eye-related topics at his channel Good Optometry Morning. Here, he explains in detail how glaucoma is diagnosed.*

What is glaucoma? (0:12)

Glaucoma is a genetic eye disease that affects the optic nerve. It impacts about 4% of people aged 40-80 and is a leading cause of blindness in people over 60. In susceptible people, the nerve is more delicate and deteriorates under increasing pressure, damaging nerve fibers and causing vision loss.

• Glaucoma is asymptomatic until nerve damage is severe. The eyes feel and look fine, with no vision changes. Glaucoma that goes undiagnosed and untreated, however, will lead to blindness.

States Nelson, “It’s really important that you get this diagnosed, and it’s important you get it diagnosed early.”

No glaucoma ‘test’ (0:55)

There isn’t a single test to definitively identify glaucoma. Instead, there are several tests that, collectively, can give a good indication of whether or not someone has the disease. If overall results are inconclusive, a person may be deemed higher disease risk or a “glaucoma suspect.”

The diagnostic process (1:44)

An eye doctor will conduct some or all of these common tests to determine your glaucoma risk profile.

Personal history (1:50)

Knowing a person’s family and health history is the first step. This will reveal glaucoma risk factors including:

• Age
• Race (African, Hispanic, and Asian heritages are at increased risk)
• Parents or siblings who have glaucoma
• Past eye injuries
• Strong glasses prescriptions
• Steroid use
• Blood circulatory problems

Eye pressure testing (2:17)

Knowing your eye pressure is the next step, which can be determined in multiple ways. Normal eye pressure is about 11-20 mmHg (millimeters of mercury). Most people fall within this range, but people above this range are at risk for glaucoma. That said,

• People can have elevated eye pressure and not develop glaucoma.
• People can also have normal eye pressure and develop “normal-tension glaucoma.”

Measuring corneal thickness (2:57)

The cornea is a clear, protective layer covering the front of the eye. Thinner-than-average corneas can somewhat increase glaucoma risk.

Gonioscopy (3:12)

Gonioscopy measures the angle between the iris (colored part of the eye) and cornea, where fluid drainage occurs. This test can help your doctor see if the drainage area is clogged, or if the angle has narrowed and fluid has difficulty exiting the chamber.

Optic nerve assessment (3:56)

The optic nerve has a certain appearance in glaucoma, measured by cup-to-disk ratio—the disk being the visible part of the nerve and the cup being an indented portion of the disk caused by disease damage. People with a higher ratio have a higher glaucoma risk, as more nerve fibers die and the cup gets larger. 

Optical coherence tomography (5:06)

The optic nerve consists mostly of nerve fibers coming from the retina. In glaucoma, optic nerve and retinal nerve fibers are dying and the nerves are thinning. Optical coherence tomography (OCT) uses light waves to measure the thickness of these nerve layers.

Visual field test (5:54)

Visual field testing is typically the last glaucoma test performed. To measure your peripheral (side) vision—one of the first casualties of glaucoma—, you’ll look into a machine with dim, flashing lights on either side and click a button for each light flash seen. 

These tests may need to be repeated in order to make a diagnosis or an accurate determination of glaucoma risk.

*Good Optometry Morning: YouTube Eye Doctor. (2021, February 9). GLAUCOMA DIAGNOSIS: what tests eye doctors use to diagnose glaucoma [Video file]. YouTube. Retrieved from https://www.youtube.com/watch?v=X45T56YHjro