The patient's condition didn't improve after doctors tried several treatments, the study said.

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"People live by the philosophy that if a little bit is good, a lot is better," Richard Rosen, the director of Retina Services at New York Eye and Ear Infirmary of Mount Sinai, and lead investigator of the case, said in a statement. "This study shows how dangerous a large dose of a commonly used medication can be."

Normal dosages of the drug are known to cause disturbances in vision, researchers said, but those symptoms typically resolve within 24 hours. Researchers warned this particular case shows taking too much of erectile dysfunction drugs could lead to long-term vision problems.

"Our findings should help doctors become aware of potential cellular changes in patients who might use the drug excessively, so they can better educate patients about the risks of using too much," said Rosen.

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