Visual field loss, or visual field defects, occur when there are areas of the vision which are blacked or grayed out. Often, this is due to a problem within the eye or the brain that results in a loss of part of the vision.
Within the eye, conditions like glaucoma and macular degeneration can result in specific patterns of visual field loss. In the brain, a stroke or a tumor may cause visual field loss of a quadrant or entire half of the vision.
Understanding the possible causes of visual field loss helps to guide the diagnosis of conditions in both the eye and the brain.
What is the Visual Field?
A person has a set amount of the world which can be viewed at one time without moving the head or the eyes.
This area of vision includes a central vision and peripheral vision and is collectively the visual field.
Therefore, any type of vision loss can be categorized as a partial or complete visual field defect.
How are Visual Field Defects Measured?
The brain is naturally prone to accommodate for any missing vision in one or both eyes by filling in the vision with the best guess of the area.
Because the brain is so quick to adapt to visual field loss, it may be completely asymptomatic or have symptoms that are less bothersome than would be expected given the amount of vision that has been lost.
To accurately determine if there has been any visual field loss, an instrument called a visual field analyzer or perimeter is used.
This instrument requires patching one eye and focusing on a central location or target. Once these parameters are met, the instrument then shows small lights to measure the sensitivity of certain areas of the vision.
Visual Field Defects from Glaucoma
Glaucoma causes visual field loss in the periphery and slowly advances into central vision loss.
These visual field defects may present as a nasal loss, an arcuate defect through the upper or lower vision, or an entire half of the vision missing.
Typically, visual field defects from glaucoma will not be noticed but mobility may become more difficult or you may bump into things more frequently.
Visual Field Defects from Macular Degeneration
Macular degeneration impacts the center portion of the vision called the macula.
With macular degeneration, the vision in the center will be blurred initially and as the condition worsens, it will become black and form a visual field defect.
Since these defects are centrally located, they are much more likely to cause symptoms that are rapidly perceived and any changes are noted as well.
As macular degeneration progresses and the center of the vision is damaged, the eye may begin to fixate with a non-central point to achieve better vision and avoid the large central visual field defect.
Visual Field Defects from Tumors or Strokes
A brain injury in the form of a compressive tumor or stroke (cerebrovascular accident), may cause a visual field defect if the area of the brain affected is responsible for visual processing.
The occipital, temporal, and parietal regions of the brain are all likely locations of these types of brain injuries that can result in visual field defects
These visual field defects will be symmetrical and respect the vertical and horizontal midline since the optic nerve fibers split once they are within the brain.
Using only a visual field and the resulting visual field defects, the location of a stroke or tumor can be predicted and verified with imaging.
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