STUDIES

Visual Fields

Amsler Grid

Amsler Grids are just graph paper with a dot in the middle which the patient is supposed to focus on. Patients cover one eye while looking at the Amsler Grid. It is then the technicians job to ask questions about what they see. Amsler Grids are only used to test the central 20 degrees of a patients field of vision not the peripheral. If a patient is complaining of distortions it is important to use the Grid so that the patient can mark where distortions are seen.

Confrontation Fields

This is testing visual fields with fingers only. It is mostly used for screening purposes just to check the peripheral vision. The benefit to confrontation fields is that no special equipment is needed and it is a quick way to get an idea of a patients peripheral vision.

  1. The patient covers one eye
  2. The patient looks at the examiner’s nose
  3. The examiners holds his fingers up, equidistant from him to the patient, in the patients inferior, superior, nasal, and temporal peripheral fields and asks the patient to tell him how many fingers are being held.
  4. This test is repeated for the other eye.

Automated Perimetry

This requires special equipment and takes longer than confrontation fields. This is the most common way providers use to track patients with visual field defects.

  1. The patient must keep their chin in the chin rest and forehead against the forehead rest.
  2. The eye not being used must be covered with a patch
  3. The patient must always look at the fixation light
  4. The patients date must be put  in. The patients current prescription and age are necessary data that the machines needs to calculate the trial lenses.
  5. The following should be monitored:
  • Fixation Loss – how many times the patient looks away from the central target. This number must be less than 4.
  • False Positives – This is when the patient responds when no stimulus is present. This tests the patients understanding of the test.
  • False Negatives – This is when the patient at first responds to a dim light, but later in the test does not respond to a brighter light in that same location. The purpose of false negatives is to test the patients alertness.
  • Stimulus Brightness – This represents how bright a stimulus had to be before the patient would see it. A number of 0 represents no vision in that area. The larger the number the better.

Three common reasons to use an automated perimeter

  1. Monitor glaucoma. One way a physician monitors glaucoma is to pre from periodic visual field tests.
  2. Testing for stokes/brain injury
  3. Test for Ptosis – ptosis is the drooping of the eyelids. To perform this test a patient is tested on their superior field of vision then the test is repeated with the patient’s eyelids taped up. This is referred to as a “taped/untaped test.”

 

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