Apraclonidine test for Horner syndrome.
A. Before drops administered (suspected left Horner syndrome).
B. After drops administered. Note the slight “reversal of anisocoria” in the left eye and the resolution of ptosis.
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.