A picture made available March 27 2015 shows Andreas Lubitz, co-pilot of Germanwings flight 4U9525, running the Airportrace half marathon in Hamburg, Germany, Sept 13, 2009. [Photo/IC]

BERLIN - The co-pilot suspected of crashing a passenger jet in the Alps may have been suffering from a detached retina but investigators are unsure whether his vision problems had physical or psychological causes, a German newspaper said on Sunday.

Bild am Sonntag also reported how the captain of the Germanwings Airbus had screamed "open the damn door!" to the co-pilot as he tried to get back into the locked cockpit before the jet crashed last Tuesday, killing all 150 on board.

Another German newspaper, Welt am Sonntag, quoted a senior investigator as saying the 27-year-old co-pilot Andreas Lubitz "was treated by several neurologists and psychiatrists" and that a number of medications had been found in his apartment.

Police also discovered personal notes that showed Lubitz suffered from "severe subjective overstress symptoms", he added.

Lufthansa, the parent company of the budget airline, said the carrier was unaware of a psychosomatic or any other illness affecting Lubitz. "We have no information of our own on that," a Lufthansa spokesman said.

A spokesman for state prosecutors in Duesseldorf declined to comment on Sunday on the various media reports, adding there would be no official statement before Monday.

The mass circulation Bild am Sonntag said investigators had found evidence that Lubitz feared losing his eyesight,apparently because of a detached retina.

However, it was unclear whether this was due to an organic failure or psychosomatic illness, when physical problems are thought to be caused or aggravated by psychological factors such as stress.