Bryce Harper’s blurry vision was blamed on dehydration. How does that happen?

When right fielder Bryce Harper started to experience blurred vision during Sunday’s Phillies game, eventually seeing “splotches” that did not clear up with eye drops, the team took no chances. They took the slugger out of the game against the San Diego Padres after the fifth inning.

Luckily for Harper (and his 64-60 team’s chances to make the postseason), the culprit turned out to be readily treatable. On this humid August afternoon — with the temperature hitting 90 degrees in Philadelphia, likely higher on the field — the star outfielder was suffering from dehydration. His vision returned to normal after he was given intravenous solution.

Though the cause of Harper’s sudden vision trouble may seem benign, it made sense for the team to take it seriously, said Beeran Meghpara, a corneal surgeon at Wills Eye Hospital who was not involved in the player’s care.

Sudden loss of vision can be caused by a variety of underlying medical issues — some of them quite serious, such as a stroke. Dehydration is a relatively minor issue, at least at first, but it is important to treat promptly before more serious problems arise.

Dehydration can impair vision in one of two ways, said Meghpara, co-director of the refractive surgery program at Wills. One is simply dry eye.

“If you’re dehydrated, your eyes can dry out,” he said.

Contact lens wearers may be especially prone to this condition in hot weather, the physician said. The problem can be treated with eye drops, though it may not clear up for a few minutes. If that’s what happened to Harper, the drops apparently did not work fast enough.

The other form of vision loss tied to dehydration is more serious. A person can become so dehydrated that blood pressure declines to the point of light-headedness, Meghpara said. That means a decline in blood flow, and thus oxygen, to cells in the eye.

“Things kind of go gray,” he said.

It is unclear which issue affected Harper. The Phillies took his condition seriously enough that they hooked him up to an IV, getting fluids into his bloodstream immediately. Most people can combat dehydration by simply drinking water, Meghpara said.

Some fans have expressed surprise that the team was not keeping better tabs on a player’s fluid intake, especially one who is paid tens of thousands of dollars for every at-bat.

“It happens to the best of us,” Meghpara said. “It was really hot [Sunday]. People just have to consciously think about staying hydrated and drinking plenty of water, especially when doing strenuous activity.”

It also happened to the now-deceased Phillies pitching ace Roy Halladay after one particularly laborious effort in 2011.

Harper was active on Sunday, for sure. He walked, singled, and scored a run before he came out of the game. He also threw out a runner at second base, notching his ninth assist of the season.

“I feel better now. It’s weird,” Harper said after the game, which the Phillies lost, 3-2. “An hour ago, I couldn’t see in front of me, kind of. Now I feel fine.”

Yet he still had a headache, and he asked TV camera crews to turn down their lights.

He is expected to be back in action for Tuesday’s game against the Red Sox. The temperature at the start of the game in Boston is forecast to be a relatively comfortable 76 degrees.

But, Bryce: It still might be a good idea to keep a water bottle handy.