The prison cell that has been Jason Rezaian’s home for most of the past 141 days has no mattress. He has slept on blankets on the hard floor and awakened each morning with back pain, for which he has received no treatment.

He suffers from chronic eye infections that have persisted for so long his family fears permanent damage to his vision. For more than a month, he has been afflicted by a groin inflammation so painful he sometimes has trouble standing.

Almost five months after Rezaian’s still-unexplained arrest, family members say conditions in Iran’s Evin prison are taking a fearsome toll on the 38-year-old Tehran correspondent for The Washington Post. But even worse than the physical discomforts, they say, are the psychological effects from near-total isolation and uncertainty over how long the ordeal will last. The uncertainty deepened further Sunday withIran’s announcement that formal charges — still unspecified — have been filed.

“Every day, we’re in new territory,” Rezaian’s brother, Ali, a California businessman, said in an interview. “Never has a Western journalist been held this long. It’s taking a devastating toll on him, physically and mentally.”

Worry over Rezaian’s health has prompted family members to speak in unprecedented detail about his well-being as he nears the end of his fifth month in detention.

Mary Rezaian pleads for the Iranian government to release her son, Washington Post correspondent Jason Rezaian, and his wife Yeganeh Salehi. The two were arrested on July 22 on undetermined charges in Tehran along with another couple. Rezaian remains in custody, while Salehi and the couple have all been released. (Provided to The Washington Post)

In interviews, relatives spoke of his growing despair in recent weeks as Iranian officials repeatedly dangled the possibility of freedom and then took it away again.

Iranian officials have kept Rezaian in solitary confinement for most of his time in detention, never allowing him to meet his attorney and permitting only a handful of visits with his wife and one other relative, family members say.

He was not allowed to contact his U.S.-based family until two weeks ago, when he was permitted to call his mother on Thanksgiving Day.

“At first, I thought he sounded great, but as we talked, I could tell he wasn’t,” Mary Breme Rezaian said of the conversation. “We tried to talk about past things and previous Thanksgivings, but we both kept breaking down in tears.”

Rezaian, a San Francisco native and son of an Iranian immigrant, was arrested at his Tehran home July 22 with his wife, Iranian journalist Yeganeh Salehi. She was released on bail in October, but Iranian officials extended Rezaian’s detention for an additional two months, citing an ongoing investigation.

In Iran, the filing of formal charges sometimes can lead to a release after a bail hearing, but it also throws new uncertainty into the case, including the possibility of more delays, according to human rights experts familiar with the country’s legal system.

“In national security cases, the judge can renew temporary pretrial detention indefinitely,” said Faraz Sanei, an Iran researcher for Human Rights Watch. “And [the judge] can prevent lawyers speaking to clients or accessing files.”

No public explanation has been provided for the arrests, and Iranian officials did not respond to an e-mail requesting comment for this article.

Some experts have speculated that Rezaian has been caught up in a domestic power struggle between Iranian political factions feuding over Tehran’s recent diplomatic opening toward the West. Iran’s influential Human Rights Council secretary, Mohammed Javad Larijani, last week called the case a “fiasco” and expressed hope that the matter would be quickly resolved.

The Obama administration, which is engaged in negotiations with Iran over its nuclear program, has stepped up pressure on Iran’s government in the past week.

On Sunday, Secretary of State John F. Kerry urged Iran to drop the charges against Rezaian, saying the journalist “poses no threat to the Iranian government or to Iran’s national security.” A State Department spokesman said Tuesday that the United States remained “committed to returning Jason Rezaian to his family, friends and loved ones.”

But with no end to the ordeal in sight, the Rezaian family’s frustration is growing. Relatives have begun to speak more candidly, drawing on details provided by visitors to paint a portrait of Rezaian’s life since his arrest. Their account, which matches descriptions by former inmates of Evin prison, depicts an endless cycle of physical deprivation, extreme isolation and frequent interrogations apparently aimed at coercing Rezaian to confess to wrongdoing.

“It is constant pressure for him: psychological pressure, interrogation tactics,” Ali Rezaian said. “They’re trying to manipulate his psychological state, to get misinformation to make him more compliant with what they want him to do.”

Since the day of his arrest, relatives say, Rezaian has been mostly kept in solitary confinement in Evin, a fortress-like prison on Tehran’s outskirts originally built by Iran’s last monarch, Mohammad Reza Pahlavi. Former prisoners who spent time in Evin’s solitary-confinement unit described cramped cells that are miserably hot in the summer and cold in winter.

One former inmate, Iranian-born scholar and author Haleh Esfandiari, recalled a lack of amenities other than a sink, a pair of blankets and a Koran. Esfandiari spent 105 days in Evin and, like Rezaian, had no mattress.

“The door is locked, and you’re on your own,” said Esfandiari, who now directs the Middle East Program at the Woodrow Wilson International Center for Scholars, a Washington think tank.

“To go to the bathroom, you have to knock on the door. The whole idea [is] to move you to despair, to make you feel isolated,” she said. “They keep repeating that no one in the outside world cares about you.”

For Rezaian, the ordeal has been complicated by health problems. The journalist was being treated for high blood pressure at the time of his arrest, and family members worried that a combination of stress and a lack of access to medicine could aggravate his condition.

Rezaian eventually was given an Iranian version of his blood-pressure medication, but in

the meantime, other problems emerged.

His chronic eye infections went untreated for weeks, and the symptoms have continued since the prison recently began administering eye drops, family members said.

More troubling is a testicular inflammation that surfaced about a month ago and causes bouts of excruciating pain, family members said. In recent days, Rezaian was given a sonogram to determine the cause of the inflammation, but the results of the tests are not yet known.

“They’ve been undertreated,” Ali Rezaian said of his brother’s medical problems. “He has been able to see a doctor twice, but in both cases it took over a month of efforts and him complaining about conditions.”

He described his brother as “very depressed, almost to the point of losing hope.”

Rezaian’s surprise telephone call at Thanksgiving brought a measure of relief, ending a four-month drought in direct contact between the prisoner and his U.S. relatives.

Mary Rezaian said she spoke with her son for half an hour, but she was acutely aware that others were present in the room with her son and listening to the conversation.

“There were topics I could not begin to address,” she said. “Both of us were bemused to be speaking to one another. There was not advanced warning, so we couldn’t really prepare.”

Although other journalists have been arrested in Iran, Rezaian did not expect that he would be targeted, his mother said.

Rezaian had taken great care not to touch any of the tripwires that had gotten other journalists in trouble with Iran’s Ministry of Culture and Islamic Guidance, the agency that grants credentials to foreign journalists.

“He knew about the high-

profile cases where people had broken the rules,” she said. “He followed the rules.”

She said her son did not complain about his plight during his Thanksgiving phone call other than to express regret about upsetting the family’s holiday plans. Before his arrest, Rezaian had expected a visit home for the holidays with his wife, the first since their recent marriage.

“I was really hoping to bring Yegi this year,” he told his mother, using his wife’s nickname.

Mary Rezaian tried to be reassuring during the call, thinking at the time that her son probably would be released soon, she said. After all, he had not been charged with a crime, and the clock was running down on the 60-day extension that had kept him locked up since October.

“The expectation was that we’d be seeing each other,” she said.

The announcement of formal charges against Rezaian came nine days later.