Shatner's reaction both to the line "he's dead already," where it hits him that Spock is about to die, as well the sheer look of horror when Spock gets up to come near him and Kirk realizes Spock is blind and walks into the divider, are what sells just how god-awful the situation is.
Blinded again.....more seriously this time. So much for the inner eyelid, at least at that moment.