The Collaborative International Dictionary of English v.0.48:

Photopsia \Pho*top"si*a\, n. [NL., fr. Gr. fw^s, fwto`s, light +
   'o`psis sight.] (Med.)
   An affection of the eye, in which the patient perceives
   luminous rays, flashes, coruscations, etc. See phosphene.
   [1913 Webster]