The only sure way to diagnose glaucoma is with a complete eye exam. A glaucoma screening that only checks eye pressure is not enough to find glaucoma.
During a glaucoma exam, your ophthalmologist will:
Measure your eye pressure
Inspect your eye’s drainage angle
Examine your optic nerve for damage
Test your peripheral (side) vision
Take a picture or computer measurement of your optic nerve
Measure the thickness of your cornea Glaucoma is usually picked up during a routine eye test, often before it causes any noticeable symptoms.
It’s important to have regular eye tests so problems such as glaucoma can be diagnosed and treated as early as possible. Early treatment can help stop your vision becoming severely affected.
You should have an eye test at least every two years. If you’re at a higher risk of glaucoma, for example, if you have a close relative with it, you may be advised to have more frequent tests.
Tests for glaucoma
There are several quick and painless tests that can be carried out to diagnose and monitor glaucoma.
Eye pressure test
An eye pressure test (tonometry) uses an instrument called a tonometer to measure the pressure inside your eye.
A small amount of anesthetic (painkilling medication) and dye is placed onto the front of your eye. A light from the tonometer is gently held against your eye to measure the pressure inside.
High pressure in your eye can be a sign that you have glaucoma or are at increased risk of developing it.
Gonioscopy is an examination of the front outer edge of your eye, between the cornea (transparent layer at the front of your eye) and the iris (the colored part of your eye).
This is the area where the fluid should drain out of your eye.
A gonioscopy can help to determine whether this area (called the “angle”) is open or closed (blocked), which can affect how fluid drains out of your eye.
Visual field test
A visual field test – sometimes called perimetry – checks for missing areas of vision.
You may be shown a sequence of light spots and asked which ones you can see. Some dots will appear in your peripheral vision (around the sides of your vision), which is often affected by glaucoma, to begin with.
If you can’t see the spots in your peripheral vision, it may indicate the glaucoma has damaged your vision.
Optic nerve assessment
The optic nerve (the nerve connecting your eye to your brain) can become damaged in glaucoma, so an assessment may be carried out to see if it’s healthy.
For the test, eye drops will be used to enlarge your pupils. Your eyes are then examined with a slit lamp (a microscope with a bright light) to assess your optic nerve.
The eye drops used to widen your pupils could temporarily affect your ability to drive, so you’ll need to make arrangements for getting home after your appointment.
Optical coherence tomography
Optical coherence tomography (OCT) is a type of scan where special rays of light are used to scan the back of your eye and produce an image of it.
This can help detect any damage to the retina (the light-sensitive layer at the back of the eye) or optic nerve caused by glaucoma.
Referral to a specialist
If glaucoma is picked up during an eye test, you should be referred to an ophthalmologist (eye doctor) for further tests.
Your ophthalmologist will confirm your diagnosis and find out:
- How far the condition has developed
- How much damage glaucoma has done to your eyes
- What may have caused the glaucoma