Understanding Visual Field Testing

• 1). You might think of your visual field as if it were a dart board. The bull's-eye is the central field of vision. Central vision sees fine detail and helps you read, sew, and write. The outer rings are the peripheral field and help you become aware when something appears to the side, above, below, or from behind you when you are looking straight ahead. You rely on your peripheral vision when you are driving, walking, and playing sports. All the rings between the peripheral field and the central field are called the paracentral field. Loss of vision in any of these areas can affect your quality of life and may even indicate serious physiological conditions.
  
  
• 2). Find out what field of vision tests measure. A field of vision test measures how well you can see throughout your visual field---the central field (straight ahead), the peripheral field (all around the edges), and the paracentral field (in between the central and peripheral fields). By having you stare straight ahead and then testing your ability to see things in each area, the eye doctor can detect the presence of one or multiple scotomas, or blind spots. Mapping out the location of a scotoma can help diagnose diseases of the eye (for example, retinitis pigmentosa) or brain disorders, such as stroke or traumatic brain injury.
  
  
• 3). Learn the definition of scotoma. A scotoma is the loss of vision, or blind spot, in a particular area of your visual field. When this blind spot occurs on the edges of your visual field, or the periphery, daily activities may not be affected very much. However, if the scotoma affects the core of your visual field and you lose the central vision that lets you see fine detail, your life may be seriously impacted. Scotomas can be of any size, shape, or location within the visual field and their detection and measurement can determine the cause.
  
  
• 4). Discover what a scotoma may indicate. The appearance of a scotoma can have different causes depending on the placement, shape, and size of the blind spot. Glaucoma produces a specific pattern of visual field loss as does retinal cell death due to eye diseases such as retinitis pigmentosa. Optic nerve damage due to toxic influences, stroke, or acquired brain injury can also cause scotomas.
  
  
• 5). Understand what the field of vision test may reveal. A field of vision test is often used when determining whether a person is officially vision-impaired. To be recognized as legally blind by the Internal Revenue Service, Social Security Administration (SSA), vocational rehabilitation agencies, and other disability-based benefit programs, you must have a visual field of less than 20 degrees. A normal visual field is 180 degrees.