Local physicians say water balloons, once considered the harmless ammunition of playful pranksters, can cause serious damage to the eyes.

In a letter to the Journal of the American Medical Association, three physicians from the University of Utah Health Sciences Center cite the case of a 23-year-old man who was hit in the right eye by a water balloon while watching a football game.The water balloon was fired from a "giant slingshot more than 300 meters (990 feet) from the stadium," the doctors said. The man passed out briefly and was taken to an emergency room at the U. Hospital.

The damage was devastating.

When first examined, the vision in his right eye was so bad he couldn't see how many fingers doctors were holding up at arm's length from his face.

The eye was swollen, blood vessels in the eye were broken, muscles were damaged, vitreous fluid was leaking and the bony socket surrounding the eye was badly fractured. After the swelling went down, doctors found the man's eyeball had been pushed backward into the orbit.

Three months after surgery and follow-up treatment, the man still had poor sight in the eye, and constant double vision forced him to wear an eye patch.

Doctors named the previously unreported cause of orbital injury "water balloon orbitopathy." They noted that a second case has been reported involving a student struck in the right eye by a water balloon while riding on the hood of a car.

Other playful pastimes are also hazardous to eyesight.

Colleen Malouf, executive director of the National Society to Prevent Blindness, Utah Affiliate, says blows to the eye are common.

"In fact, the thrill and excitement children experience competing in sports is overshadowed by an epidemic of eye injuries," she said. "Most of the 160,000 eye injuries suffered annually by American children occur during play or sports, including baseball, football, basketball, field hockey and tennis."

Malouf said tennis balls routinely travel at 50-80 mph and may gain speeds of up to 125 mph.