Visual Field Testing

During a routine eye exam, some eye doctors may want to determine through visual field testing the full horizontal and vertical range of what you are able to see peripherally. This is commonly referred to as "side vision."

Visual field tests assess the potential presence of blind spots (scotomas), which could indicate eye diseases. A blind spot in the field of vision can be linked to a variety of specific eye diseases, depending on the size and shape of the scotoma.

Many eye and brain disorders can cause visual field abnormalities. For example, optic nerve damage caused by glaucoma creates a very specific visual field defect. Other vision problems associated with blind spots developing within the visual field include optic nerve damage (optic neuropathy) from disease or toxic exposure or damage to the light-sensitive inner lining of the eye (retina).

Brain abnormalities such as those caused by strokes or tumors can affect the visual field. In fact, the location of the stroke or tumor in the brain can frequently be determined by the size, shape, and site of the visual field defect.

Confrontation visual field testing typically is used as a screening visual field test. One eye is covered while the other eye fixates on a target object, such as the doctor's open eye, while the doctor stands or sits directly in front of you. You then are asked to describe what is seen on the far edges or periphery of your field of view. As an example, your eye doctor may hold up different numbers of fingers within your peripheral field of view and ask how many can be seen while you continue to fixate on the doctor's eye.

A patient undergoes visual field testing with a Humphrey Field Analyzer (HFA), which uses automated perimetry to measure responses to visual stimuli appearing in central and side vision. (Photo courtesy of Carl Zeiss Meditec)

If an eye disease is suspected, you may need to undergo more comprehensive, formal types of visual field testing to evaluate how well you see across a wide range of vision. Numerous tests for measuring visual field loss exist, and can include:

• Automated Perimetry: Various forms of automated perimetry tests measure your responses to the presence of objects in different areas of your field of view. While your head is held still, usually with a chin rest inside a large bowl-like instrument, you stare (fixate) on a source of light straight ahead. A series of random lights of different intensities are flashed in your peripheral field of vision. You then press a button or use other means to indicate your response when you perceive the computer-generated light suddenly appearing in your field of view. If you are unable to see objects in an appropriate portion of your field of view, then you may have a blind spot indicating vision loss.
   
• Frequency Doubling Perimetry: Frequency doubling is based on an optical illusion that uses vertical bars of contrasting colors such as black and white appearing on a screen. These bars appear to double in number when they alternately flicker at higher frequencies, a phenomenon thought to be due to the unique response of specific light-sensitive cells (photoreceptors) within the eye's inner back lining (retina). Inability to see vertical bars at certain frequencies could indicate optic nerve or other types of eye damage with accompanying loss of vision in certain areas of the visual field.

 

• Electroretinogram: This test automatically measures the way cells within the eye's light-sensitive inner layer (retina) respond to different flashing light stimuli, resulting in creation of a pattern of responses or "map" used for evaluating vision loss. This test is conducted by placing a device that detects electrical impulses (electrode) on your eye's clear outer surface (cornea), which is treated with a topical anesthetic to ease any potential discomfort. The electrode then automatically detects responses from your eye's retina. The results can be directly related to the part of a visual field that might be defective. This is based on the anatomical relationship of the retinal images and the visual field.