<div class="form-group">
        <p>Have you worn contact Lens before?</p>
        <input type="radio" name="lenses"  value="Yes"/> Yes<br>
        <input type="radio" name="lenses"  value="No"/> No<br>
</div>
<div class="form-group">
        <p>If yes, which type of disposable contact lens have you worn before?</p>
        <input type="checkbox" name="disposable_lens[]"  value="Monthly"/> Monthly<br>
        <input type="checkbox" name="disposable_lens[]"  value="Daily Disposables"/> Daily Disposables<br>
</div>

if(isset($_POST["submit"]))
{
if(empty($_POST["lenses"]))
{
    $error .= '<p><label class="text-danger">Lenses is required</label></p>';
}
else
{
    $lenses = clean_text($_POST["lenses"]);
}
if(empty($_POST["disposable_lens"]))
{
    $error .= '<p><label class="text-danger">Disposable_lens is required</label></p>';
}
else
{
    $disposable_lens = array_map('clean_text', $_POST["disposable_lens"]);

$mail->Body = join('', array(
        "Outlet: ",
        $_POST['outlet'],
        "<br/>",
        "Full Name: ",
        $_POST['fullname'],
        "<br/>",
        "Email Address: ",
        $_POST['email'],
        "<br/>",
        "Phone Number:",
        $_POST['contact_no'],
        "<br/>",
        "Have you worn contact lens before?: ",
        $_POST['lenses'],
        "<br/>",
        "If yes, which type of disposable contact lens have you worn before?: ",
        join(', ', $_POST['disposable_lens']),
        "<br/>",
        "Appointment Date ",
        $_POST['date'],
        "<br/>",
        "Appointment Time ",
        $_POST['time']
        ));