The Collaborative International Dictionary of English v.0.48:

Skiascope \Ski"a*scope\, Sciascope \Sci"a*scope\, n. [Gr. ? a
   shadow + -scope.] (Med.)
   A device for determining the refractive state of the eye by
   observing the movements of the retinal lights and shadows. --
   Ski*as"co*py, Ski*as"co*py, n.
   [Webster 1913 Suppl.]