He went on to study medicine at Limoges, and then in Paris in 1869. When the Franco-Prussian War broke out in 1870, he went to serve as a doctor with the Red Cross, where he earned a medal for Unusual Bravery. After the war, Parinaud returned to Paris to continue his studies.
His thesis for medical school was on optic neuritis in acute meningitis in children, which earned him respect and recognition in the field
His other fields of work included multiple sclerosis, ophthalmoplegic migraine, hysteria, supranuclear lesions, and concomitant squint. All in the realm of neurology.
Parinaud also worked in the physiology of vision, where he worked on role of the visual receptors, the light sense, night-blindness, and color vision. He is well known for the medical term Parinaud"s syndrome, which is, "A dorsal midbrain lesion such as pinealoma which results in vertical gaze palsy, convergence-retraction nystagmus and light-near dissociation".