、。
Everything in front of me went completely dark.
Literal
I [of-の] eye [of-の] before [subject-が], completely dark became.
目の前 ('before one's eyes, in front') is a set expression, literally 'the front of the eye.' 真っ暗 ('pitch dark') uses the intensifier 真っ to mean 'completely, truly.' The に+なる marks the change into that state. A common metaphor for losing consciousness or experiencing sudden despair.