There are many different eye conditions that are associated with congenital nystagmus; theoretically, any bilateral visually-significant pathology present at birth or in infancy during the critical period of visual development may interfere with the development of stable fixation (1) Eventually I'll get around to discussing the finer points of nystagmus; but for now, I'm sticking to some basic study stuff.
Corneal dystrophies are clinically fairly rare (with notable exceptions) but have pretty easily identifiable appearances. Because we have learned quite a bit about the genetics, inheritance, etc. about many of the dystrophies, this seemed to be a pretty popular topic on tests – though it seemed like in the past few years the number of questions on corneal dystrophies decreased quite a bit. I don’t know the minds of the test-writers, so who knows if it was a random thing, or if there was more emphasis on clinically significant questions.
There are TONS of causes of leukocoria (white pupil). But this can be a very important differential, as it can be the presenting sign of some sight-threatening and life-threatening conditions (most obviously retinoblastoma). Because of its clinical importance, it is essential to be able to not only recognize what it is, but to also have a decent differential diagnosis so that you don’t miss out on any key causes when conducting a history and physical.