In 1910-11 with parasitologist Stanislaus von Prowazek (1875-1915) of the Hamburg Tropical Institute, he was a member of a scientific expedition to Samoa, where he worked as a private lecturer.
It was here that Leber discovered the effects on the eye caused by filarial infections by the parasite Wuchereria bancrofti.
In 1913-14 he took part in the Medizinisch-demographische Deutsch-Neuguinea-Expedition to German New Guinea with physician Ludwig Külz (1875-1938) and painter Emil Nolde (1867-1956).
At Madang, Java he became a director in a hospital for eye and tropical diseases, and it was in Leber's clinic that Max Dauthendey died from malaria in August, 1918.
During World War II he spent much of his time interned at a camp for German prisoners in Dehradun, India, and after his release became head of ophthalmology at the Prince of Wales Hospital in Bhopal.