But in a new study published today in the journal Pediatrics, University of Michigan researchers found it is likely scarlet fever had nothing to do with Mary's blindness.

Senior author Beth A. Tarini, M.D., and her co-authors used evidence from newspaper reports, Laura Ingalls' memories and school registries to conclude Mary's blindness was probably caused by viral meningoencephalitis.

"Since I was in medical school, I had wondered about whether scarlet fever could cause blindness because I always remembered Mary's blindness from reading the Little House stories and knew that scarlet fever was once a deadly disease," says Tarini, an assistant professor of pediatrics in the Child Health Evaluation and Research Unit at the University of Michigan's C.S. Mott Children's Hospital.

"I would ask other doctors, but no one could give me a definitive answer, so I started researching it."

Mary Ingalls went blind in 1879 at age 14. Tarini and her co-authors found evidence in Laura Ingalls Wilder's memoirs and letters that described Mary's illness as "spinal sickness" with symptoms suggestive of a stroke.

The study quotes a local newspaper item that reports that Miss Mary Ingalls was confined to her bed and "it was feared that hemorrhage of the brain had set in (sic) one side of her face became partially paralyzed."

"Meningoencephalitis could explain Mary's symptoms, including the inflammation of the facial nerve that left the side of her face temporarily paralyzed," Tarini says, "and it could also lead to inflammation of the optic nerve that would result in a slow and progressive loss of sight."

It's not surprising that scarlet fever was labeled the culprit in the books instead, Tarini says. Between 1840 and 1883, scarlet fever was one of the most common infectious causes of death among children in the United States.

"Laura's memoirs were transformed into the Little House novels. Perhaps to make the story more understandable to children, the editors may have revised her writings to identify scarlet fever as Mary's illness because it was so familiar to people and so many knew how frightening a scarlet fever diagnosis was," says Sarah S. Allexan, B.A., lead author of the paper and a medical student at the University of Colorado.

For reasons that remain unclear, scarlet fever case fatality rates fell dramatically in the early 20th century, well before antibiotic treatment.

But even now, a scarlet fever diagnosis can strike fear into the heart of parents Tarini sees in her pediatric practice.

"Familiar literary references like these are powerful -- especially when there is some historical truth to them." Tarini says. "This research reminds us that our patients may harbor misconceptions about a diagnosis and that we, as physicians, need to be aware of the power of the words we use -- because in the end, illness is seen through the eyes of the patient."

Additional authors: Carrie L. Byington, M.D of the University of Utah.; Jerome I. Finkelstein, M.D., F.A.C.S., assistant professor of Opthalmology and Visual Sciences at the University of Michigan.