Carl Koller studied medicine at the University of Vienna. At first Kollers interests were in embryology and experimental pathology, but soon Koller switch to ophthalmology. One of his teachers shared with him the need for a local anesthetic in eye surgery. Koller, eager to make a large contribution, experimented with various solutions on animals, but had no luck.
Koller interned at the Allgemeines Krankenhaus. He lived on the same floor as Sigmund Freud, who was also interning. Freud invited Koller to work with him studying the physiological effects of cocaine. Koller experimented with cocaine on his own tongue and noticed a numbing effect. He used cocaine on the eye of a guinea pig and found that it numbed the area so well that the eye was completely insensitive to pain. The use of cocaine as a local anesthetic became Kollers most important discovery. He would be recognized later in life with numerous awards.
Due to strong anti-Semitism in Europe, Koller was not promoted within the medical field. Consequently, he moved to New York City and became a renowned surgeon and diagnostician at Mount Sinai Hospital. Koller had a highly successful clinical practice for 56 years.