While Mary Ingalls and her eyesight issues was periodically addressed in the early episodes of Little House on the Prairie, such as the season two episode Four Eyes. In this episode Mary first gets glasses, but she didn’t actually become blind until later in the series.
Mary eventually does lose her eyesight in season four, in the the two part season finale episodes, I’ll Be Waving As You Drive Away (Part One) and I’ll Be Waving As You Drive Away (Part Two). This transitions the series to have a heavy focus on the school for the blind, where Mary Ingalls first attends and then later becomes a teacher, eventually opening a school for the blind in Walnut Grove.
