Loss of part of the normal area of vision in one or both eyes
Visual field defects take different forms, ranging from loss of areas at the outer edges of vision (peripheral vision) or small blind spots to loss of most of the area that you normally see (the visual field). If you notice a loss of vision, you should seek urgent medical advice because visual field defects sometimes indicate a serious underlying disorder. Regular vision tests are important because visual field defects may develop slowly without being noticed.
Visual field defects may be caused by damage to the light-sensitive retina at the back of the eye; the optic nerve, along which nerve signals are carried from the retina to the brain; or the parts of the brain involved with vision.
Several eye disorders cause characteristic patterns of visual field loss. For example, a gradual increase in fluid pressure in the eye (see Chronic glaucoma) can damage nerve fibres in the retina, causing loss of peripheral vision. If glaucoma is left untreated, only a narrow area of central vision will remain (tunnel vision). Inflammation of the optic nerve (see Optic neuritis) typically causes loss of central vision, and a pituitary tumour often causes loss of the outer half of the visual field in each eye. Brain damage due to a stroke or tumour (see Brain tumour) may result in loss of the right or left half of the visual field in both eyes. Migraine can cause temporary visual field defects.
Visual field defects usually appear gradually and often remain unnoticed. In other cases, depending on the type of defect, symptoms may include:
Bumping into objects on one side.
Missing whole sections of text while you are reading.
Being able to see only straight ahead (tunnel vision).
The majority of visual field defects can be detected during routine vision tests. However, you should see your doctor immediately if you notice a change in your normal field of vision.
Your doctor may carry out a visual field test to assess the pattern and extent of the defect.
The treatment for the defect depends on the underlying cause. For example, if you have chronic glaucoma, you will be given drugs to reduce the pressure in the eye (see Drugs for glaucoma). Existing defects are usually permanent, but treatment of the underlying condition may prevent further deterioration. Many people who have a visual field defect become used to it, but it may affect their lifestyle or choice of occupation. For example, if you have tunnel vision, you should not drive.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.