What Happens at a Glaucoma Eye Exam?
If your optometrist has recommended a glaucoma assessment, or you have risk factors that warrant closer investigation, you might be wondering what the appointment actually involves. The good news is that a glaucoma eye exam is straightforward, painless and typically takes between 20 and 30 minutes. Understanding each step can help ease any nerves and ensure you get the most out of your visit.
A comprehensive glaucoma assessment usually involves four key tests. Each one looks at a different aspect of your eye health, and together they give your optometrist a complete picture of your glaucoma risk.
Tonometry: Measuring Eye Pressure
The first test most people associate with glaucoma is tonometry, the measurement of intraocular pressure (IOP). Elevated eye pressure is one of the most significant risk factors for glaucoma, though it is worth noting that not everyone with high pressure develops glaucoma, and not everyone with glaucoma has high pressure.
There are two common methods your optometrist may use. The non-contact tonometer, often called the "air puff test," directs a gentle burst of air at the surface of your eye. It is quick and requires no eye drops. The Goldmann applanation tonometer is considered the gold standard for accuracy. Your optometrist will place a numbing drop in your eye, then gently touch the cornea with a small probe. You will not feel any discomfort thanks to the anaesthetic drop.
Normal eye pressure generally falls between 10 and 21 mmHg, but your optometrist will interpret your reading alongside other findings. Pressure alone does not confirm or rule out glaucoma.
Optic Nerve Examination
Your optometrist will examine the optic nerve at the back of your eye using a bright light and a magnifying lens. In many cases, dilating drops will be used to widen your pupils, giving a clearer view of the optic nerve head.
What your optometrist is looking for is the cup-to-disc ratio, the size of the central cup relative to the overall disc. In glaucoma, the cup gradually enlarges as nerve fibres are damaged. Your optometrist will also assess the colour, shape and symmetry of the nerve between both eyes. Any asymmetry or unusual appearance may prompt further investigation.
Dilation typically takes about 15 to 20 minutes to take effect, and your vision may be slightly blurry and light-sensitive for a few hours afterwards. Bringing sunglasses to your appointment is a good idea, and you may prefer not to drive immediately after.
Visual Field Testing
Visual field testing maps your peripheral (side) vision, the area of sight most commonly affected by glaucoma. During the test, you will sit in front of a bowl-shaped instrument and focus on a central point. Small lights of varying brightness will flash in different locations, and you press a button each time you see one.
The test requires concentration, and it is completely normal to feel like you are missing some of the lights. The instrument is designed to find the threshold of your vision, so some lights are intentionally very faint. Try to stay relaxed, blink normally and respond honestly. There are no wrong answers.
The results produce a detailed map showing any areas of reduced sensitivity. Your optometrist will compare these maps over time to detect any progression. Visual field testing is one of the most important tools for monitoring glaucoma because it directly measures functional vision loss.
OCT Imaging
Optical coherence tomography (OCT) is a non-invasive imaging technology that uses light waves to create a detailed cross-sectional scan of your retina. It measures the thickness of the retinal nerve fibre layer (RNFL) surrounding the optic nerve, the very layer that thins when glaucoma damages nerve cells.
The scan takes just a few seconds per eye. You simply rest your chin on a support and look at a target inside the machine. There is no contact with your eye, no bright flashes and no discomfort at all. OCT is particularly valuable because it can detect structural changes to the nerve fibre layer before you notice any vision loss. This makes it one of the earliest indicators of glaucoma risk.
OCT imaging can detect nerve fibre thinning years before visual field loss becomes noticeable, making it a powerful tool for early detection.
Putting It All Together
No single test confirms glaucoma on its own. Your optometrist combines the results from tonometry, optic nerve examination, visual field testing and OCT imaging to form a complete assessment. They will also consider your age, family history, ethnicity and other risk factors.
If any results are outside normal ranges, your optometrist may recommend more frequent monitoring or refer you to an ophthalmologist for further evaluation. Early detection gives you the best chance of preserving your vision long-term.
Not sure whether you have risk factors worth investigating? G-Screen's free educational risk check can help you understand your risk profile in about 6 minutes. And when you are ready to book a comprehensive eye exam, you can find an optometrist near you.