Not quite.
while (<STDIN>)
is equivalent to
while ($_ = <STDIN>)
but when spelled out explicitly, they're both
while (defined($_ = <STDIN>))

>perl -MO=Deparse -e"while (<STDIN>) {}"
while (defined($_ = <STDIN>)) {
    ();
}
-e syntax OK

>perl -MO=Deparse -e"while ($_ = <STDIN>) {}"
while (defined($_ = <STDIN>)) {
    ();
}
-e syntax OK
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