Constant Loiseau (1838-1890), inventor of the optometer, was born in Namur, Belgium. He lost his father at an early age. Like his father, he decided to become a doctor in the Belgian army, specialising in ophtalmology.
His optometer, designed to measure eye refraction, proved extremely useful to catch men who tried to avoid having to join the army by pretending their eyesight was poor.
Loiseau died of diabetes in 1890 in Leuven but his optometer was in use until the first World War.