In which scripture is the story in which Radha was originally born blind, and opened her eyes when she met Krishna found?
Padma Purana , Patala Khanda, Chapter 71 (5.71.29-31) describes that Vrishabhanu, the father of Sri Radha perceived her to be motionless, blind and deaf and requested the sage Narada to have a look at her.
Then, when the best sage, after having talked to the excellent cowherd, decided to go, Bhanu spoke to him like this: "O god, I have (also) a daughter, resembling the wife of a god. She is younger than this boy(Bhanu's son). Her form (i.e. she) is dull and blind and deaf. Prompted by the desire for her prosperity, I seek a boon from you, O most glorious one. By just casting a pleasing glance at the girl make her quite composed."
I heard that Narada advises Vrishabhanu to call all the cowherds announcing the birth of daughter. Nanda and Yashoda also arrived with Krishna. When child Krishna comes in front of Radha, Radha becomes active and opens her eyes. I don't have any reference for this though.