On the failure of completion of lines passing through the blind regions related to the optic disc, and to scotomas of migraine auras.

We compared the appearance of a line passing through the optic-disc blind spot with that of lines passing just medial or just lateral to the blind spot. Though there is no well-defined gap in the line, we see a consistent difference, which is hard to describe. On the other hand, during a migraine aura experienced by one of us, lines passing through scintillating scotomas showed clear sharply defined gaps.