Major depressive disorder (MDD) is a frequent and particularly disabling disorder. The efficacy of current antidepressants is limited, with 50-60% of patients not achieving a sufficient response to treatment. Indeed, to date, clinicians are unable to predict the therapeutic response a patient will obtain to a given molecule. This often results in several trials of a molecule until clinical efficacy is achieved, with a delay of several months of untreated disease. Achieving faster efficacy by targeting the right molecule for each patient in the 1st line of treatment would limit the morbidity and mortality induced by MDD, and its impact on quality of life. To achieve this goal rapidly, there is a need to identify markers for predicting and monitoring therapeutic response to antidepressants.

This is why the MESANTIDEP study aims to propose electroretinographic (ERG) biomarkers for predicting therapeutic response at 12 weeks for the two main therapeutic classes of antidepressants prescribed as 1st-line treatment for major depressive disorder: Selective Serotonin Reuptake Inhibitors (SSRIs) and alpha-2 adrenergic receptor antagonists (alpha-2 antagonists). Secondly, investigators will look for ERG biomarkers of therapeutic response at 6 weeks, and 12 weeks, for these two therapeutic classes of antidepressants.

For this purpose, patients diagnosed with MDD and requiring the initiation of an antidepressant - of the SSRI or alpha-2-antagonist class - will be included. At their inclusion visit, patients will not yet have started their antidepressant treatment and will undergo various tests. These include clinical questionnaires, sleep assessment questionnaires and three ERG tests (fERG, PERG and mfERG). Antidepressant treatment can be started by the patient the day after the inclusion visit. 6 and 12 weeks later, the patient undergoes the same tests as at the inclusion visit to monitor their therapeutic response to the prescribed antidepressant. The identification of electrophysiological markers predictive of therapeutic response to antidepressants is intended to help clinicians in the treatment of MDD patients. More rapid therapeutic intervention tailored to each patient will limit the functional impact, improve quality of life and reduce the morbidity and mortality associated with the disease. These electrophysiological ERG measurements are easy to perform. They are therefore accessible to all, and can be used, through a multimodal approach, in routine clinical practice.

Inclusion Criteria:

• Diagnosis of a current unipolar depressive episode according to DSM-V criteria
• Prescription of antidepressant treatment - SSRI or alpha-2 antagonist - by the psychiatrist or referring physician for the current depressive episode
• Age 18 or more
• Affiliation with a welfare scheme and native French speakers
• Complete information on the study received and written informed consent signed

Exclusion Criteria:

• Diagnosis of a progressive psychiatric disorder (except MDD and anxiety disorder) according to DSM-V criteria
• Seasonal character of the depression
• Current antidepressant treatment
• Recommended antidepressant treatment other than SSRI or alpha-2 antagonist
• High suicide risk
• Retinal or ophtalmologic pathology affecting visual acuity as assessed by the Monoyer scale.
• History of head trauma, epilepsy or other neurological disorders
• Participation in another interventional study (including exclusion period)
• Intellectual disability leading to difficulty participating or impossibility or inability to understand the information provided on the study.
• Persons cited in Articles L. 1121-5 to L. 1121-8 of the French Public Health Code: pregnant women, parturient or breastfeeding mothers, persons deprived of their liberty by a judicial or administrative decision, persons under psychiatric care under duress, persons admitted to a health or social establishment for other goals than research, minors, adults subject to a legal protection, adults who are unable to express their consent and who are not subject to a legal protection measure.
• Criteria incompatible with the use of the ERG device: open wound in an area covered or enveloped by the device; implantable medical device (e.g. pacemaker); user at high risk of contagion