Do any of you have a link to the medical codes used when doctors file medical claims?

I saw a specialist for my eyes today. He is well versed in dry eyes and how to treat them, but he is used to dealing with post lasic patients and not with people with Sjogren's Syndrome. We need to file on our medical insurance because we have no vision coverage. He did not have the codes for Sjogren's and wasn't sure the best way to file the paperwork in order to get us some coverage.

I appreciate any help for this.

Billye