Holoprosencephaly (HPE) is a complex brain malformation resulting from incomplete cleavage of the prosencephalon, occurring between the 18th and 28th day of gestation, and affecting both the forebrain and face, which results in neurological manifestations and facial anomalies of variable severity.

A fold of skin starting above the medial aspect of the upper eyelid and arching downward to cover, pass in front of and lateral to the medial canthus.