What metaphors are used in Samson Agonistes, and Shorter Poems by John Milton?

In "When I Consider," Milton deals for the first time with his total blindness, which came upon him at age 43 in 1652, when this poem is thought to have been written. The metaphor he chooses, "my light is spent," makes perfect literal sense even while implying that life itself, in a sense, has ended for him.