Levene enrolled at Columbia University and in his spare time conducted biochemical research, publishing papers on the chemical structure of sugars. In 1896 he was appointed as an Associate in the Pathological Institute of the New York State Hospitals, but he had to take time off to recuperate from tuberculosis.
This graph shows the median age of the resident population of the United States from 1960 to 2015. In 2015, the median age of the United States population was approximately 37.7 years.
Presbyopia is widespread in the United States. According to U.S. Census Bureau estimates, in 2014 more than 150 million Americans were age 40 and older, and the country is growing older: The median age reached 37.7 that year, up 2.4 years since 2000.