Visual field defect, a blind spot (scotoma) or blind area within the normal field of one or both eyes. In most cases the blind spots or areas are persistent, but in some instances they may be temporary and shifting, as in the scotomata of migraine headache. The visual fields of the right and left eye overlap significantly, and visual field defects may not be evident without specific testing of each eye separately. Causes of visual field defects are numerous and include glaucoma, vascular disease, tumours, retinal disease, hereditary disease, optic neuritis and other inflammatory processes, nutritional deficiencies, toxins, and drugs.

Causes of Visual Field Defect
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 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. Inflammation of the optic nerve 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 may result in loss of the right or left half of the visual field in both eyes. Migraine can cause temporary visual field defects.

Symptoms of Visual Field Defect
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).

What might be done?
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. 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.