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.