Second set of clear eyelids

part of the genetic tailoring for Nilfeheim colonists.

To better see underwater a second eye lid was genetically added to their biological make up.

Many Terramn Life forms have a form of that.

The nictitating membrane (from Latin nictare, to blink) is a transparent or translucent third eyelid present in some animals that can be drawn across the eye from the medial canthus for protection and to moisten it while maintaining vision.