Source : Webster's Revised Unabridged Dictionary (1913)

Nyctalopia \Nyc`ta*lo"pi*a\, n. [L. nyctalopia, fr. nyctalops a
   nyctalops, Gr. ?. Gr. ? meant, a person affected either with
   day blindness or with night blindness, and in the former case
   was derived fr. ?, ?, night + ?, ?, the eye; in the latter,
   fr. ? + ? blind + ?.] (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}.

   Note: Some writers (as Quain) use the word in the opposite
         sense, night blindness. See {Hemeralopia}.

Source : WordNet®

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