Final answer:
The epic poem Beowulf does not mention the protagonist, Beowulf, having bad eyesight. The tale focuses on his battles with monsters such as Grendel and a dragon, highlighting themes of heroism and the fight between good and evil.
Step-by-step explanation:
The question "what caused Beowulf's bad eyesight" appears to be based on a misinterpretation of the text. In the Old English epic poem Beowulf, there is no specific reference to the protagonist, Beowulf, having bad eyesight. As a work of literature, Beowulf relates the tale of its heroic protagonist, who fights against various monsters, including Grendel, Grendel's mother, and later in his life, a dragon. The poem focuses on themes of heroism, loyalty, and the struggle between good and evil. It is possible that a translation or adaptation of Beowulf makes creative alterations, but in the traditional and historical texts of the poem, Beowulf's eyesight is not discussed or mentioned as impaired.