Tests are done for glaucoma in order to determine whether you have glaucoma, if so what sub-type of glaucoma, and to monitor the situation going forward, to make sure that your situation is stable.
During your visit, some or all of these tests may be done. Some will be done by a technician or ophthalmic assistant, and some will be done by the doctor.
Although reading, or central, vision is not affected until the very late stages of the disease, a vision check will be done at most visits. This is usually done for distance, with your best distance glasses on, if used.
High pressure does not necessarily mean that you have glaucoma, and normal eye pressure does not mean you don’t have glaucoma. However, higher eye pressure is an important risk factor for glaucoma and the only one that is altered by any of our current treatments. Furthermore, eye pressure can vary throughout the day, so it will be tested at all glaucoma visits. Many ways to test eye pressure are used. Some use a puff of air, while others use a small device to gently touch the front of the eye. If this is used, eye drops will be used to numb your eye. The test that is considered the best standard uses a a yellow drop placed into the eye and blue light with a small contact prism. Whatever the technique, the procedure is called “Tonometry”.
The eye produces fluid and it leaves the eye through the “trabecular meshwork”, often called the “drain” of the eye. A special lens may be placed over your eye to allow the doctor to look at the drainage system in your eye and to see whether it is open or shut.
The front layer of the eye (the “cornea”) is of different thickness in different people. It can be helpful to know the corneal thickness in glaucoma patients, and this can be measured with a small ultrasound probe or with a laser measuring device.
A slit lamp is an illuminated microscope that is used to look at your eye in detail for both the front and back parts of the eye. You will have to rest your chin and forehead against the headrest and the doctor will shine a light into the eye. Sometimes certain lenses are used to gain more information, such as with gonioscopy, or to see the back of the eye in better detail. Glaucoma causes loss of nerve fibers in the optic nerve and this can be seen through the microscope.
These are some of the tests your eye doctor can order:
This test assesses the sensitivity of your peripheral, or side vision, but can also be used to check central vision in certain cases.
There are different ways to take this test, most of the time we use a machine. The test flashes small lights and they become dimmer as the test progresses, as the test is looking for the dimmest light that you can see. It is a hard test and it is normal to miss spots and the test will always try some spots that are too dim for you to see. The most important part of the test is to look steadily at the center light and not look away. The small test flashes of light occur around the center light. You will click the button each time there is a flash. It is easy to look toward where light flashes, but moving the eye will result in a poor quality test. It is important to click WHENEVER you see a dim light, and not wait for a brighter one to be sure, but it is also very important NOT to click unless you did see a dim light. Your test results are compared by the software to normal individuals who are the same age. Sometimes it can take a few tests to get used to the testing and get reliable results.
Glaucoma has a classic pattern of visual field loss involving your peripheral vision first. When looking at the results, the black spots are where you do not see as well as most people of your age. As glaucoma progresses, the black spots become larger and your field of vision becomes smaller.
Patients with glaucoma have damage to the optic nerve over time and it is important to have ways to track changes in the optic nerve. Apart from visual fields, doctors may use a combination of the following image tests to follow your optic nerve. Depending on which province you are in and the arrangement your eye doctor has, you may be asked to pay a fee for some of these tests.
OCT takes a cross sectional picture through the layers of the back of the eye. It can be used to image the optic nerve as well as the center area for vision. It measures the thickness of the nerve fibers in the back of the eye. In glaucoma, the nerve fibers are lost and this can be tracked with this imaging over time.
HRT also uses light to image the nerve and creates a 3D image of the optic nerve and can be compared over time. This gives a different view of the optic nerve.
You may be asked to take pictures of the nerve in the back of your eyes to compare to in the future. These are plain photos taken with a camera to document your nerve.