When I hand the referral to the patient I always explain to him/her all the clinical findings and the need to be referred. I always put the letter in an unsealed envelope and I say to the person that he/she is free to read it.
If the person does not want to take the letter to the doctor, that is his/her own responsability. However I have come across with many elderly people with memory problems coming by themselves to have their eyes tested. It is ONLY in this circumstances when I prefer to send the letter directly to the doctor because I evaluate what I think it is more beneficial to the patient.