What are Visual Fields
Visual field: The entire area that can be seen when the eye is directed forward, including that which is seen with peripheral vision. The visual field can be tested to measure the extent and distribution of the field of vision
What is Visual Field Testing?
Visual field test: A test that measures the extent and distribution of the field of vision.
A visual field test may be done via a number of methods, including:
- confrontation visual field testing
- Amsler grid
- tangent screen
- automated perimetry
Why do VF testing?
- Many diseases can adversely affect the visual field, including: • glaucoma • strokes (CVA) • Tumors
- Medications can also affect the visual field • E.g., hydroxychloroquine (Plaquenil) toxicity
- Occupational safety standards are determined by VF’s • Driver’s license qualification • Pilots (private, commercial, military)
- Determination of functional loss • Benefits for loss of vision • Insurance reimbursement (cosmetic vs. medically necessary)
Visual field screening
- Generally done when VF loss unlikely, but possible
* Should be quick, easy, and capable of eliciting a wide variety of defect
Qualitative or diagnostic field testing
Designed to determine the characteristics of a VF defect (location, borders, shape, size, etc.)
• For example: special DL testing, ptosis functional loss assessment, etc.
Quantitative visual field testing
- Fully quantifies a known or suspected defect, so future changes detectable
- Requires automated (full threshold) perimetry
The why and when of VF screening?
- Incidence of visual field loss about 3-5% (10-15% in those over age 65).
- One study (n=1500) found 4.4% of those appearing for first optometric eye exam had VF defects and in half the cause was sight- or life-threatening.
- VF defects are often asymptomatic and may be the only detectable evidence of a disease/disorder.
Confrontation Visual Fields
- Can be done in multiple ways
- A quick, simple way to screen for gross VF loss
- Does not require special equipment and can easily be done with homebound or bedridden patients
- Sensitivity not very high (better for posterior visual pathway lesions than anterior pathway lesions)
Technique for Confrontation VF’s (counting fingers)
How far away does the examiner sit in front of the patient?
Examiner sits facing patient (about a meter in front of them)
Technique for Confrontation VF’s (counting fingers)
Is this test done with one eye or both?
Patient covers one eye (test is done on each eye separately). Have patient look straight ahead into appropriate eye of examiner.
Technique for Confrontation VF’s (counting fingers)
Should they wear their glasses or contact lenses?
No for glasses
Can wear contacts
Technique for Confrontation VF’s (counting fingers)
How many fingers should the examiner use?
Examiner introduces fingers (one, two, or four) in each quadrant while making sure patient maintains fixation straight ahead (into their eye)
What are tips to obtaining reliable confrontation VF’s?
- Make sure target presented to your patient at corresponding point in your own VF (assumes you have normal fields).
- Don’t make it too hard or too easy!
- Make sure entire target remains completely within the quadrant you intend to assess.
- Recognize deceptive responses (feigned sight or malingering) and know how to detect it.
How & when to assess the central VF?
• Central field loss is usually, but not always, associated with reduced visual acuity.
• Therefore, unlike peripheral VF’s, central VF loss is not routinely screened for.
When macular disorders are suspected, function should be assessed via some form of central VF testing:
Common methods for assessing central VF’s include:
- Amsler grid testing
* Specialized automated VF test strategies
What is Amsler grid testing?
A simple, quick way to check for defects within the central portion of the visual field.
How many degrees does the Amsler grid test measure?
Assesses roughly the central 10 degrees of the VF
What area of the eye does the Amsler grid assess? Is this a qualitative or quantitative assessment?
A qualitative, rather than quantitative, assessment of macular function (macula = portion of retina responsible for central vision).
What are indications for using the Amsler grid?
- Should be done to detect gross abnormalities that may be caused by suspected disorders of the macula (e.g. AMD, etc.)
- May be given to patients with instructions on how to use themselves at home to monitor such conditions themselves .
What is a normal response to the Amsler grid?
Normal response is:
• Dot at center seen when looking directly at it.
• All for corners seen when looking at dot.
• No areas of the grid missing
• No areas of the grid distorted (no “wavy lines”)
What is an abnormal response to the Amsler grid?
Anything abnormal indicates a defect of the central VF. • This may confirm macular dysfunction in someone suspected of having a macular disorder • Also used to monitor for change in those with known defects
Normal visual fields should be:
Normal VF’s:
• Full in extent (up, down, left, and right) both eyes.
• Free of “blind spots” (within visual field).
• Free of areas of distortion (within visual field).
