The Collaborative International Dictionary of English v.0.48:

Nyctalopia \Nyc`ta*lo"pi*a\ (n[i^]k`t[.a]*l[=o]"p[i^]*[.a]), n.
   [L. nyctalopia, fr. nyctalops a nyctalops, Gr. nykta`lwps.
   Gr. nykta`lwps meant, a person affected either with day
   blindness or with night blindness, and in the former case was
   derived fr. ny`x, nykto`s, night + 'w`ps, 'wpo`s, the eye; in
   the latter, fr. ny`x + 'alao`s blind + 'w`ps.] (Med.)
   (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.
       [1913 Webster]

   Note: Some writers (as Quain) use the word in the opposite
         sense, night blindness. See Hemeralopia.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Moonblink \Moon"blink`\, n.
   A temporary blindness, or impairment of sight, said to be
   caused by sleeping in the moonlight; -- sometimes called
   nyctalopia.
   [1913 Webster]

WordNet (r) 3.0 (2006):

nyctalopia
    n 1: inability to see clearly in dim light; due to a deficiency
         of vitamin A or to a retinal disorder [syn: nyctalopia,
         night blindness, moon blindness]