What does "nyctalopia" mean?

Nyctalopia: (a) A disease of the eye, in consequence of which the patient can see well in a faint light or at twilight, but is unable to see during the day or in a strong light; day blindness. (b) See Moonblink. Note: Some writers (as Quain) use the word in the opposite sense, night blindness. See Hemeralopia.