Democratic presidential candidate Joe Biden’s left eye filled with blood during an appearance on a CNN town hall Wednesday.

As he answered a question about climate change, the former vice president’s eye turned red, and the Washington Examiner suggested it might have been caused by a broken blood vessel, a condition known as a subconjuctival hemorrhage.

It can be caused by a number of things — including sneezing, coughing, straining, eye rubbing, trauma from injury, high blood pressure or a bleeding disorder​ — according to WebMD.

​As a senator, Biden​ ​had emergency surgery twice for life-threatening brain aneurysms in 1988.

Biden, 76, wrote about the experience in his 2007 book, “Promises to Keep.”

​”Maybe I should have been frightened at this point, but I felt calm,” ​Biden wrote. “In fact, I felt becalmed, like I was floating gently in the wide-open sea. It surprised me, but I had no real fear of dying. I’d long since accepted the fact that life’s guarantees don’t include a fair shake.”

His campaign released an untimely tweet Wednesday, saying: “We can’t turn a blind eye to the way in which environmental burdens are distributed unevenly along racial and socioeconomic lines.”

“Don’t turn a Bloodshot eye either,” posted ALX.

The Biden campaign declined to comment.