We always thought that Laura Ingalls Wilder's sister Mary, in the Little House on the Prairie Books, lost her sight due to the infamous scarlet fever as mentioned in the book.
Looking at the symptoms mentioned in the book, scientists are of the opinion that it could be brain inflammation that caused the Character, Mary, in the book to go blind.
To understand the reason behind Mary's blindness, researchers went through local newspapers, and letters and other work of the author.
The symptoms mentioned matched with a disease called meningoencephalitis, which is a swelling of the spinal cord and brain, caused by several viruses.
Researchers now believe that since scarlet fever was so well known at that time, editors of the book actually thought Mary's blindness was due to scarlet fever.
"Meningoencephalitis could explain Mary's symptoms, including the inflammation of the facial nerve that left the side of her face temporarily paralyzed. It could also lead to inflammation of the optic nerve that would result in a slow and progressive loss of sight."