The Afterimage Test
This test involves stimulating the macula of each eye so as to produce a different linear afterimage in each eye, 1 horizontal and 1 vertical, by having each eye fixate on a linear light filament separately. The test can also be performed by covering a camera flash with black paper and exposing only a narrow slit; the center of the slit is covered with black tape to serve as a fixation point, as well as to protect the fovea from exposure. Because suppression scotomata extend along the horizontal retinal meridian and may obscure most of a horizontal afterimage, the vertical afterimage is induced in the deviating eye and the horizontal afterimage in the fixating eye. The patient is then asked to draw the relative positions of the perceived afterimages. Possible perceptions are shown in Figure 7-12. In patients with eccentric fixation (see Chapter 6), the afterimage is extrafoveal, and the test cannot be interpreted.
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.