Seth damaged an eye of his nephew Horus in a battle. The latter was taking revenge of his father Osiris killed by Seth. Next, Horus gave his eye repaired by Thoth to Osiris, so that he lived again. Wedjat eyes are the repaired eye of Horus, symbolic of resurrection. They were made in an infinity of materials and variants throughout all Dynastic Periods and are with scarabs the most common amulets. There are right and left eyes, sometimes double-sided like the two right examples below
Incised amazonite, flat back, pierced for suspension L 1.3, H 1.0, T 0.4 Before Dynasty 22
Biconvex diorite, pierced for suspension L 3.0, H 2.2, T 1.0 Third Intermediate Period Private collection DA
Green glazed steatite, pierced for suspension L 1.4, H 0.8, T 0.3 Dynasty 21