hello,just wondering if any of you can help me. we got our tax credit exemption certificate a month or so ago. i am just wondering how it works. i need to sign up to a dentists so will ALL dentists charges be free or is there a catch? i wear glasses and im way over on having a test. again,does ANY optitans except the certificate? it says on letter that your entitled to * free sight tests. *a full value of a voucher towards the cost of glasses. so do i need to pay anything? thanks in advance.