Welcome to the fun world of Ophthalmology/Optometry coding! There is a lot of information out there on the web, but I happen to like this site. It has a lot of clear articles about the finer points of eye coding:
http://www.corcoranccg.com/
The short answer to your question of when to bill 92xxx codes vs 99xxx codes is: it depends on the documentation and the payer. If your ophthalmologist is seeing routine eye exams and billing to vision plans, most of them request 92xxx codes. If s/he is seeing problems/medical eye exams, there's more variety but in general most payers in my experience prefer the 99xxx codes. This is just a general rule, though. Also, the documentation requirements are stricter with the 99xxx codes so if your doc's documentation isn't up to snuff, sometimes 92xxx codes are the way to go.
Lastly, as a tie-breaker, it's sometimes good to check out the fee schedules on your major payers. If the documentation supports a 99214, you might want to use that instead of a 92012, for instance. On the other hand, if your documentation only supports a 99213, you might be better off using a 92012.
I hope this helps, and good luck!
