package my::model::subclass;

use strict;
use warnings;

use base qw/my::model/;

our %normal = ( top_level_key => { name1 => value1,
                                   name2 => value2,
                                 },
              );

# the rest of the package...

##</code><code>##

package my::model;

use strict;
use warnings;

sub use_subclass_package_var {
    my ($self, @cols) = @_;
    my $normal = join '::', ref $self, 'normal';

    foreach my $col (@cols) {
        #
        # I need help getting the next line to work properly
        #

        next unless exists eval { %{$normal{$col}} };

        # the rest of the code
    }
}

##</code><code>##

my $obj = my::model::subclass->new();
$obj->use_subclass_package_var('top_level_key');