"Blind eyes could blaze like meteors and be gay": Like meteors, these men's eyes are bright, vivid, and yet in some ways inhuman. They seize attention, just as meteors light up the night sky.
Throughout the poem, night and darkness are used as metaphors for death, while light and day represent life.
Words forking lightning: Forking lightning serves as a metaphor for leaving lasting change, just as redirecting lightning changes its course.
Deeds dancing: Their deeds could have been the center of attention, frolicking for all to see.
Catching and singing the sun in flight: The men the stanza discusses adventured, full of vitality, but "learned too late" that their efforts were ultimately fruitless, like someone trying to catch the sun.
Blind men who see with blinding sight: These men may be literally blind, as Thomas's father was as his death approached, but they also may be figuratively blinded by their age. Yet in spite of their blindness, their insights are so bright and brilliant that they can blind others.