Pope Benedict XVI
Pope Benedict XVI is to step down at the end of February (Reuters)

Pope Benedict XVI had been so weighed down by the pressures of the job that he lost the sight in one eye and dropped "a considerable amount of weight", according to his biographer.

German journalist Peter Seewald, who is writing an official biography of 85-year-old Joseph Ratzinger, said Benedict looked exhausted at their last meeting in the Apostolic Palace in December.

"[His] hearing had gone down, he was blind in the left eye, his body had grown thinner," Seewald wrote in German magazine Focus and Italian Corriere della Sera.

"He didn't look ill but it was impossible not to notice the fatigue that laid hold of him," Seewald said. "I had never seen him so exhausted."

The Catholic Church leader shocked the world when he announced he would resign at the end of February because of old age and declining strength.

Seewald said Ratzinger was already considering the almost-unprecedented move when they last met.

"'What should we expect from your papacy?' I asked him," Seewald wrote. "'From me? Not much. I am an old man and strengths are leaving me. I believe what I have already done to be enough'.

"'Are you thinking of retiring?' 'It depends on what my body will impose'."

Some Vatican observers said Benedict decided to step down after reading a damning report by a commission of three cardinals on the Vatileaks scandal. The report was reportedly handed to Ratzinger at around the same time as his last meeting with the biographer.

"During a conversation at Castel Gandolfo [the Pope's summer residence], I asked him if he had been shaken by Vatileaks. 'I don't let myself [fall] to universal despair,' he answered. 'I simply find it unconceivable.'"

"[Benedict] maintained that the scandal didn't caused him to lose his bearings or feel the strain of his office, 'because it can always happen'," Seewald added.

According to Italian magazine Panorama, the Vatileaks report revealed power struggles and infights in the Holy See that made Benedict feel betrayed by some of his closest aides.

"Ratzinger has never sought power. He has dodged the Vatican's plots and tricks," Seewald said.

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