How do I use inserted values using getopts

I have this bash code combined with getopts and if I understood getopts correctly OPTIND contains the index of the next command line option and all the command line options provided to shell script are presented in the variables $1, $2, $3 etc.. Correct me if I am wrong but basically the same concept as local variables in the functions.

So according to this why options [-a somevalue ] or [-b somevalue ] won't give me any results. What am I doing wrong?

OPT_A=A
OPT_B=B

while getopts :a:b FLAG; do
 case $FLAG in
    a) 
      OPT_A=$OPTARG
      ;;
    b) 
     OPT_B=$OPTARG
      ;;
  esac
done

shift $((OPTIND-1))

    while [ $# -ne 0 ]; do

if [[ -z $OPT_A ]]; then
    if [ `echo $1 | grep -o '\.' | wc -l` -ne 3 ]; then
        echo "Parameter '$1' does not look like an IP Address (does not contain 3 dots).";
            exit 1;
        elif [ `echo $1 | tr '.' ' ' | wc -w` -ne 4 ]; then
            echo "Parameter '$1' does not look like an IP Address (does not contain 4 octets).";
        exit 1;
            else
        for OCTET in `echo $1 | tr '.' ' '`; do
                if ! [[ $OCTET =~ ^[0-9]+$ ]]; then
                        echo "Parameter '$1' does not look like in IP Address (octet '$OCTET' is not numeric).";
                        exit 1;
                elif [[ $OCTET -lt 0 || $OCTET -gt 255 ]]; then
                        echo "Parameter '$1' does not look like in IP Address (octet '$OCTET' in not in range 0-255).";
                        exit 1;
                fi
        done
    fi
fi


if [[ -z $OPT_B ]]; then
        if [[ "$2" =~ ^[0-9]+$ ]] && [ "$2" -ge 1 -a "$2" -le 10000 ]; then 
            echo "chosen variable: $2";
            exit 1;
            else echo "variable $2 is not in range '1 - 10000'";
            exit 1;
        fi
    fi

    done
    exit 0