Abnormal pupil morphology Persistent pupillary membrane 2009-05-02T05:51:28Z The tunica vasculosa lentis anterior (pupillary membrane) normally undergoes atrophy in the third trimester of pregnancy. If the membrane does not completely atrophy, then remnants of membranous structures can be observed to emrge from the iris. The presence of remnants of a fetal membrane that persist as strands of tissue crossing the pupil. SNOMEDCT_US:95500008 UMLS:C0344541 HP:0009917