You can use split to break you comma separated matches into individual pieces:
use strict;
use warnings;
my $line = 'FIELDS=(1,10,3,A,11,10,7,D,9,10,11,A)'
if ( my ($fields) = $line =~ /FIELDS=(\(.*\))/ ) {
my @vars = split /,/, $fields;
# do whatever you want with @vars
}