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After scratching his eye during the Vikings loss to the Chicago Bears, coach Mike Zimmer underwent a procedure to repair a torn retina and all seemed to be well. He was back coaching at Winter Park the same day.

But four weeks later Zimmer was forced to undergo emergency surgery because the tear evolved into a detached retina. It needed to be fixed immediately or he risked going blind in that eye.

Zimmer, 60, apparently scratched his right eye during the game against Chicago. In most cases, most people don't even know they've torn their retina until they go in for a routine eye exam, said Aaron Shukla, associate professor and director of the ophthalmic technician program at St. Catherine University. Small tears usually don't cause vision problems but larger tears can cause people to see flashing or "floaters" that look like little insects flying by, he said.

Tears, which can be the result of aging, medical conditions or trauma, need to be repaired because they can lead to a detached retina and that could cause blindness, Shukla said. The repair done with a laser is a minor procedure most often done in a doctor's office or clinic, Shukla said. Other than having to wear dark glasses because the eyes were dilated during the procedure, the patient can be back to most normal activities, he said.

A week after the first repair, Zimmer was back on Nov. 8 for a second procedure. Shukla doesn't know the specific details of Zimmer's case but said the second procedure likely would have been to repair another tear if Zimmer was back at work immediately afterward.

Vikings General Manager Rick Spielman said the head coach had no issues after the second surgery until he experienced vision problems after Wednesday's practice. A third procedure was scheduled for Friday.

It's not uncommon that multiple procedures are needed to repair a tear, according to doctors.

The laser repairs work about 50 percent of the time, said Dr. Sandra Montezuma, an opthalmologist and an assistant professor in the University of Minnesota's Department of Ophthalmology and Visual Neurosciences. Or, sometimes a new tear develops, she said.

But if doctors later discovered the retina had detached, there would be no waiting, Shukla said. "It needs immediate surgery or you risk blindness," he said. It's a major operation done in a hospital.

A detachment occurs when the retina, a thin layer of tissue at the back of the eye, pulls away from its normal position and is separated from the blood vessels that provide oxygen and nourishment, according to the Mayo Clinic.

A common method of repairing the detached retina is to place a bubble filled with gas inside the eye to hold the retina in place, Montezuma said. The bubble usually remains in the eye for four to eight weeks and patients cannot fly during that time, she said. The gas would disappear on its own.

For patients who need to fly, silicone oil could be used in the bubble. But the patient would have to return for another surgery to have it removed, Montezuma said. It's unclear what method doctors used to repair Zimmer's retina.

After word got out Wednesday that Zimmer was undergoing an emergency eye surgery, fans waited to learn whether the coach would be on the field Thursday night for the Vikings game against the Cowboys. By Thursday morning, it was clear: Zimmer would be home recuperating, not on the field. Missing the game was tough news for the hard-driving Zimmer but Spielman said after a "heart-to-heart" talk about what's important in life, he realized that losing vision in an eye wasn't worth the risk over missing one NFL game.

Now it's just a matter of waiting to see how the eye responds to the surgery, Spielman said. "It's only been 12 hours."

Recovery from the surgery can vary from a week up to six, depending on where the detachment occurred and how large it was, Montezuma said.

"If you work on a computer, you could be back at work in a week because you can see out of your other eye," she said. The vision in the repaired eye will be blurry until the bubble is gone.

"The surgery to repair the detatched retina is successful 80 to 90 percent of the time, Montezuma said. For those cases when it doesn't work, another surgery is needed, she said.

Once healed, the prognosis is good and patients can get 20/20 visions or close to it, Montezuma said. If the detatchment reached the macula, the patient's vision might not get back to 20/20, she said.

Mary Lynn Smith • 612-673-4788