Little House on the Prairie: Season 4, Episode 21

4 - 21: I'll Be Waving as You Drive Away (1)

Long hours studying by candlelight for the state teacher's exam results in tired, blurry eyes for Mary Ingalls, prompting a routine visit to the eye doctor; but when Charles is told that Mary's worsening sight is just the beginning of a much more serious problem, the concerned father can't bring himself to tell his beloved daughter that she will, most certainly, soon be completely blind.