“As a rule, men worry more about what they can't
see than about what they can.”
- Julius Caesar
Testing the Visual Field
Visual field testing helps us understand the type of loss, the completeness of the loss, the density of the loss, the presence of any sparing of the macular or central vision, and the possible location of the cause of the visual field loss.
Visual field defects from stroke and brain injury can vary greatly. When we look at only forms of hemianopsia we still find great variation. The methods used to test visual fields will also result in differences. Clinicians should not rely only on the computerized visual fields to fully define the visual field loss.
Threshold Computerized Visual Field Testing
Computerized automated threshold visual field testing has become the standard in most ophthalmic practices. Threshold field tests are not always able to define small amounts of sparing of the central vision, the macular region. Additionally the limits of these tests may fail to detect some peripheral conditions including retained temporal crescents or the Half Moon Syndrome.
To evaluate the visual field of an acquired brain injury patient our doctors find a combination of testing methods produces a better understanding of the shape and density of the loss. We combine computerized threshold visual fields, manual 3 mm white target testing, gross confrontation testing, Macular Sparing plot on the Amsler Grid and response to light and movement.
Testing the Density of the Field Loss
Since computerized tests do not always accurately represent the density of the visual field loss. It is helpful to test the visual fields with various types of targets. With one eye occluded, we test the impaired field in each eye with the light of a penlight, a very large target and a moving hand to help understand the density and absoluteness of the visual field loss. Various targets and motion can be tested.
Plotting Sparing or Splitting of the Macular Field
Threshold visual fields are not always accurate enough to detect small amounts of macular sparing. Sparing may mean a better outcome for reading and sometimes in travel. Plotting the boundary of the hemianopsia on an Amsler Grid chart can detect and accurately measure macular sparing. It can detect smalls amounts of sparing that may not be defined on the threshold automated perimeter.
A small target can be used to the amount of sparing of the central macular vision. Each 5mm square on the Amsler Grid chart represents 1 degree when the test chart is held at 30 cm. Macular sparing has been associated with better potential for reading and for mobility. In the photo to the right, the Amsler Grid is used to measure macular sparing.
Manual Testing of the Far Peripheral Fields
A quick manual screening of the far peripheral visual field can test areas that a routine threshold visual field does not reach.
This can discover a temporal crescent, where vision is retained with an otherwise loss from a homonymous hemianopsia or a Half Moon Syndrome, where a small crescent of loss occurs at the far temporal side of one eye within a normal field.
Here a technician uses a simple portable manual perimeter to measure the peripheral field. This instrument can also be helpful for patients who are unable to perform automated perimetry.
Please contact us if you have any questions.
The Low Vision Centers of Indiana
Richard L. Windsor, O.D., F.A.A.O., D.P.N.A.P.
Craig Allen Ford, O.D., F.A.A.O.
Laura K. Windsor, O.D., F.A.A.O.
Indianapolis (317) 844-0919
Fort Wayne (260) 432-0575
Hartford City (765) 348-2020