Andreas Lubitz, the co-pilot who crashed Germanwings Flight 4U9525 into the side of a mountain on Tuesday, killing himself and 149 passengers and crew, is reported to have been suffering from vision problems that may have threatened his career.

According to The New York Times, Lubitz, 27, was diagnosed with “vision problems,” which may have exacerbated an already existing psychiatric condition.

Investigators are exploring the theory that the severe stress and fear of losing his job as a result of the condition may have driven him to crash the Airbus A320 into the side of a mountain in the French Alps.

Andreas Lubitz was alone in the cockpit of the aircraft after manually locking the door of the cabin on a flight from Barcelona to Düsseldorf. According to recordings from the cockpit, Lubitz ignored demands from the captain to be let back in when the plane crashed.

Germanwings pilot had 'serious illness' http://t.co/c14SlwToW3 pic.twitter.com/JfeBm1SMU4

— The Independent (@Independent) March 29, 2015

A hospital in Dusseldorf confirmed Friday that Lubitz visited in February for an evaluation and again on March 10 for further treatment, but has declined to specify the condition for which he sought treatment, citing patient confidentiality. However, the hospital specifically noted that he was not being treated for depression, which adds weight to the theory that his visit to the hospital was indeed for vision problems that may have been an instigating factor in his decision to lock the cabin door and deliberately crash the plane.

According to friends and acquaintances, Andrea Lubitz, who began flying gliders at the age of 14, dreamed of becoming a pilot and being grounded would have been a major loss in his life.

Investigators found evidence in Andreas Lubitz’ apartment on Thursday that he was given a medical leave, including the day of the crash, which the airline said was kept from them. Lubitz reportedly tore up the note and threw it in the trash bin, where it was found by investigators.

A source “with knowledge of the investigation” told The New York Times that “the authorities had not ruled out the possibility that the vision problem could have been psychosomatic.”

Investigators may have already found remains of suspected killer co-pilot Andreas Lubitz http://t.co/jNJBLl3Gvt pic.twitter.com/NVqNDmQ66Z

— The Independent (@Independent) March 29, 2015

A leading theory is that depression also played a factor in Andreas Lubitz’ actions and was strengthened with the discovery of antidepressants in his apartment.

As pieces of the puzzle of what happened on the fated flight begin to come together, questions linger for the aviation industry and the families of those lost in the flight, including the question of whether Andreas Lubitz’ act was desperate and impulsive, or whether it was deliberately planned.

Prosecutor: Letter found in co-pilot's home indicates doctor declared him 'unfit to work.' http://t.co/hFJNWmcgSA pic.twitter.com/PDYRNxJMmA

— World News Tonight (@WNTonight) March 28, 2015