The eyelid ...

... is a screen, a curtain and covering, and is a sort of dwelling place and fortress. The hand could cover the eye, but before the hand came, the eye would have already have been obscured. But now the eyelid lies close by, placed above; at once it perceives the harm and puts forward the covering. Because of this the pupil also, placed under a covering, is not continually open to attack. The eye, alone of our organs, wishes to be untouched; it is veiled by the covering of the eyelid.

It is surrounded by lashes. Why?