Cocaine test for Horner syndrome.
A. Before drops administered (suspected right Horner syndrome).
B. After drops administered. Note that there is some pupil dilation in the right eye, but the amount of anisocoria is ≥1 mm.
Image credit: Kanagalingam S, Miller NR. Eye Brain 2015;7:35-46. Available online. Used under the Creative Commons Attribution - Non Commercial (unported, v3.0) License.