2020–2021 BCSC Basic and Clinical Science Course™
Chapter 6: Perimetry
Interpretation of a Single Visual Field
Identification of artifacts is the next step in evaluation of visual field test results. Common artifacts seen on automated perimetry include the following:
Lens rim. If the machine’s corrective lens is decentered or set too far from the eye, the lens rim may block more peripheral stimuli (Fig 5-6).
Inappropriate corrective lens. If an inappropriate corrective lens is used, the resulting field may show generalized depression. This commonly occurs, for example, when testing young pseudophakic patients or when the patient is wearing a contact lens that is not considered when selecting the corrective lens power.
Eyelid artifact. Partial eyelid ptosis may lead to a superior visual field defect.
Cloverleaf visual field. If a patient stops paying attention and ceases to respond partway through a visual field test, a distinctive visual field pattern may develop. Figure 6-6 shows a cloverleaf visual field, the result of the testing order of the Humphrey 30-2 perimeter, which begins testing with the points circled in this figure and proceeds outward. This pattern may also be seen if a patient is malingering.
High false-positive rate. When a patient responds at a time when no test stimulus is being presented, a false-positive response is recorded. False-positive rates greater than 15% suggest an unreliable test that can mask or minimize an actual scotoma and can, in extreme cases, result in a visual field with impossibly high threshold values (Fig 7-6). Careful instruction of the patient may sometimes resolve this artifact.
Figure 6-5 Lens rim artifact. The 2 visual fields shown were obtained 9 days apart. The visual field on the left shows a typical lens rim artifact, whereas the corrective lens was positioned appropriately for the visual field on the right (Humphrey 30-2 program).
Figure 6-6 Cloverleaf visual field. In the Humphrey visual field perimeter test, 4 circled points are checked initially and the testing in each quadrant proceeds outward from these points. If the patient stops responding after only a few points have been tested, the result is some variation of the cloverleaf visual field shown at right (Humphrey Full Threshold 30-2 program).
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.