Where is the gray line?

The gray line is a well-known surface anatomic landmark used by surgeons in the repair of lacerations involving the lid margin. To the best of our knowledge, no description of any deep or superficial anatomic counterpart of the gray line has been previously reported. We examined block resections of 51 eyelids histologically following localization of the gray line. The visualized gray line was consistently seen to correspond histologically to the most superficial portion of the orbicularis muscle, known as the muscle of Riolan. We comment on changes in gray line morphology with lid movement, and we advance a hypothesis to explain its "gray" color.