/ Dictionary / Index P protanopia: Meaning and Definition of Find definitions for: pro•ta•no•pi•a Pronunciation: (prōt"n-ō'pē-u), [key] — n. Ophthalm. a defect of vision in which the retina fails to respond to red or green. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: protanopia (Thesaurus) protanomaly protasis Related Content Daily Word Quiz: mamba Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language