You can also use eval:

#! perl
use strict;
use warnings;

{
    package Aardman;
    our @ISA = qw( Wallace Gromit );
}

{
    package main;
    my $pkg = 'Aardman';
    my $var = $pkg . '::ISA';
    my $ref = eval "\\\@$var";
    print join(', ', @$ref), "\n";
}
[download]

Output:

Wallace, Gromit
[download]

(But, for the reasons given by davido and tobyink above, you should probably just use no strict 'refs'.)