AFTER being rocked by a string of devastating med­ical problems, Secretary of State HILLARY CLINTON is now facing her most heartbreaking challenge – going completely blind!

Medical experts and Clinton family insiders told The ENQUIRER exclu­sively that the blood clot in her head may have caused catastrophic dam­age to the optic nerve and lead to her losing her eyesight. And that pros­pect has shaken to the core the gutsy politician, her husband Bill and their daughter Chelsea.

“Hillary had been suffering from vision issues related to her blackouts and memory loss, but additional testing resulted in a diagnosis that she might have a rare optical nerve condition that will lead to blind­ness,” explained a family insider. “She’s keeping this diagnosis a se­cret as she tries to figure out what to do next. Meanwhile, Bill and Chelsea are beside themselves with worry. They can’t believe this is happening.”

As THE ENQUIRER reported exclu­sively in early January, after suffering a concussion in a fall, Hillary began undergoing extensive testing to determine whether her splitting headaches, blackouts and fainting spells were caused by brain cancer.

Doctors discovered the former first lady had a blood clot in a vein that lies between the brain and the skull behind her right ear. They treated her with blood thinners to dissolve the clot, but the crisis is still far from over, say insiders. “The concussion or the clot could have caused swell­ing on the optic nerve, resulting in symptoms of headaches, blackouts and dizziness,” Dr. L. Ray Matthews, an expert on brain injuries and trau­ma, told The ENQUIRER.

“Also, since Hillary spends so much time on airplanes, she may have devel­oped a deep venous thrombosis in a leg, which traveled near the brain, causing swelling and damaging the optic nerve beyond repair. That could lead to blindness.

“This is extremely rare, but since she already had symptoms such as blackouts, the damage may have al­ready been done. I don’t know how long her optic nerve has been damaged or how long it could take for her to lose her vision if this is the case. It’s an individual matter.”

Another expert agrees that fears for Hillary’s vi­sion are well-founded.

“This is a very serious condition,” Dr. Joseph Maroon, a renowned Pennsylvania – based neurosurgeon, told The ENQUIRER. “A thrombosis can cause intercranial pressure and pres­sure on the optic nerve, which could lead to vision loss theoretically.”

The 65-year-old former senator’s medical crisis began several weeks ago when she blacked out at her home and suffered the concussion, which ultimately caused the blood clot. Af­ter nearly three days of treatment, a disheveled Hillary, wearing dark sun­glasses, left NewYork-Presbyterian Hospital without revealing the threat to her eyesight.

She smiled bravely as she returned to work at the State Department on Jan. 7, but didn’t tell staff the full extent of her medical condition.

“Her ordeal went from sad to tragic when she learned doctors believed she was going blind,” the family insider told The ENQUIRER. “It’s also a nightmare come true for Bill and Chelsea.”

The two are not only filled with fear and heartbreak over the prospects of Hillary going blind, they realize it could spell an end to her spectacular political career and dream of making it back to the White House as president.

“They had visions of her running for president in four years, and now she may be in total blind­ness by then,” noted the source.

“Hillary is trying to grasp what is happening to her health. On top of everything, she’s going to continue to have addition­al testing to hopefully rule out a cancer diagnosis.

“But for now, losing her eyesight is the most dev­astating development in her medical crisis. She cried out, ‘I’m going blind!’ after doctors presented her with a worse-case scenario.”

While Hillary’s physicians have said there was no neurological dam­age associated with the blood clot and they expect her to make a full recovery, sources close to the family believe that the prognosis is a smoke screen to cover up the severity of what she’s really facing.

“Hillary’s faith in God is being tested by these shocking develop­ments,” said the family insider.

 “She’s suddenly fragile and her health is at the brink.”

Hillary’s had a history of health woes that began more than a decade ago. She suffered a blood clot in her knee in 1998. Seven years later, she passed out in public from a stom­ach virus. Four years after that, she broke her elbow in a fall, and in 2011, she collapsed while boarding a plane.

“But going blind is the last thing Hillary ever thought she’d face,” said the source. “She’s worried sick about what’s to come.”