Truth be told, there is not very much detail that needs to be learned about embryology; after all, we've already learned embryology in medical school. At the same time, there are some key embryology concepts that are very helpful to understanding ocular disease, and may also show up on test questions. There usually seems to be at least one question that addresses embryology, and there are tons of practice questions that test your knowledge of embryology.
Funny-looking optic discs are a "fun" diversion in an ophthalmology clinic (sarcasm implied here). What was initially a routine exam immediately turns into an agonizing "is this normal or not" exercise. Part of the angst that comes from seeing anomalous optic discs is that some of the congenital disc anomalies are associated with systemic diseases. If there is concurrent visual field loss or decreased visual acuity, the challenge becomes deciding if those defects in the visual system are due to the anomalous nerve, or if there is some other ophthalmic cause that we don't want to miss.
As you can probably tell, I'm starting to skip around a little bit while I put together these OKAP review articles. I have a fairly large list of topics to cover, but hopefully these will all be helpful pieces of information. I decided to skip to aniridia, because it is one of those conditions that seems to be very popular in practice questions.