Possible Clues:

• Sounds as if I get a cover that's a cover. see?
• Close over 14 across? Can't see if it does it (6)
• Don't see how one might close this
• Cover for a seer?
• This will provide cover for the viewer
• Winking membrane
• Iris cover
• Pupil's hidden behind this
• One may have 20 lashes
• Natural ocular protector