It is the No. 1 line-item cost of Medicare reimbursement and affects more than 20 million people in the United States. Cataracts, which can have devastating effects on the eye, affect 42 percent of the population between the ages of 70 and 80, and 68 percent of the population over the age of 80, according to the National Eye Institute. Now, a University of Missouri professor has identified an important step in how cataracts form.