Automated full-threshold visual field testing is an important assessment your optometrist may recommend as part of your comprehensive eye examination. Visual field testing is used to evaluate how well the periphery of your vision is functioning; this is different to testing your central vision using standard letter charts in the exam room. The test helps to detect and monitor eye conditions – early detection is the best practice to ensure your best vision is maintained.
Many ocular conditions such as glaucoma, retinal vein occlusion, optic neuropathy, brain tumours and stroke can lead to visual field defects. It is important to measure these defects to help the diagnosis of new conditions and monitor the progression of known eye conditions. Around 50% of the eye’s retinal nerves can be lost before a patient notices a visual field defect themselves – this highlights why early detection of these conditions with the help of a visual field analyser is essential.
Our Adelaide practice is equipped with a Heidelberg Edge Perimeter, and at our Woodville practice we use the Medmont M700 Visual Field Analyser. A visual field test is generally performed one eye at a time and takes approximately 5-10 minutes per eye, with you pressing a button whenever a spot of light appears in your peripheral vision. These tests get easier with practice, so don’t be surprised if you miss a few spots in your first run!
The retinal photograph below shows a patient with advanced glaucoma in the left eye. The optic nerve is quite excavated due to significant nerve fibre loss.
CAPTION: Advanced glaucoma
This has lead to a visual field defect as seen in the test below. Sadly, as you can see, most of the top half of this patient’s vision is now irreversibly blind.
CAPTION: Results from a visual field test. Note: The NO means zero vision. Corresponding areas of the retina have been superimposed over the visual field to show which part of the retina has lost its sight.
In the early stages of glaucoma, only the peripheral vision is affected. Most people will not notice the peripheral vision loss until it is too late. Regular eye tests and early detection will prevent this from ever occurring.