Pupillometry and the problem of the quantification of depression

To date, there are no laboratory tests or biomarkers to diagnose depression; diagnosis is based on a clinical interview. This descriptive diagnosis says little about the biological causes and ignores the neurobiology of the symptoms. Pupillometry, a window into the brainstem, could help identify subtypes for personalized treatment. Apps for mobile pupillometric devices are now being tested and would pose easy-to-use solutions for the clinic.