In my experience there is no comprehensive list and they tend to approve on a case-by-case basis. They have a form where you put in the details of the item, cost, etc.
I know people who have claimed for cancer-related items (prosthesis, wigs) and for orthopaedic devices.
You could contact your local health office and ask for the HSE list - if they cover it for medical card patients then you can mention that in your VHI claim.