Is the plica semilunaris—often referred to as a third eyelid—a vestigial structure from evolution?

The plica semilunaris is a small fold of tissue in the inner corner of the eye. While some evolutionists consider it a vestigial remnant of a third eyelid found in birds and reptiles, it serves several important functions in humans. Without this support, the eyeball could shift, resulting in double vision. It also helps support the tear duct, preventing tears from running down the cheeks. In addition, the membrane traps debris, collecting the crusty material that builds up in the inner corner during sleep. Therefore, it is incorrect to claim that the plica semilunaris has no purpose. It was designed and is not the same as the bird’s third eyelid, which keeps the eyes from drying out during flight.¹