Crestor (rosuvastatin) drugs made by the pharmaceutical firm AstraZeneca and Viagra made by Pfizer are displayed in a pharmacy in Johannesburg, South Africa, May 15, 2014. Christopher Furlong/Getty Images

A 31-year-old man sustained irreversible vision problems after taking a high dose of sildenafil citrate, a popular erectile-dysfunction medication sold under the brand name Viagra, a report published in the October issue of the journal Retinal Cases said.

According to the report, the unnamed person from New York arrived at an urgent care clinic complaining of red-tinted vision in both eyes that had not gone away in two days. He told the doctors he has started seeing multicolored flashes of light and his eyes became more sensitive to light. He said the symptoms began shortly after taking a dose of liquid sildenafil citrate that he had purchased online. He also admitted to taking more than the recommended 50 mg dose.

He was diagnosed with persistent retinal toxicity, a condition linked to the high dose of medication damaging the outer retina. Despite various treatments, the patient's red tint has remained in place for more than a year.

Lead author and director of Retina Services at the New York Eye and Ear Infirmary of Mount Sinai, Richard Rosen, said in a statement that “People live by the philosophy that if a little bit is good, a lot is better. This study shows how dangerous a large dose of a commonly used medication can be. People who depend on colored vision for their livelihood need to realize there could be a long-lasting impact of overindulging on this drug.”

According to the researchers, there is evidence in both animals and humans that taking a heavy dose of the medication can be especially damaging to the eyes and in rare cases, the drug can be linked to vision loss.

Researchers examined the man's retina for evidence of structural damage at the cellular level which revealed that the man’s cones — a type of cell in the retina that allows us to perceive color — were damaged on a microscopic level by the medication. The damage was similar to that seen in other genetic disorders involving the retina, such as color blindness and in animal models of hereditary retinal disease such as retinitis pigmentosa or cone-rod dystrophy.

“To actually see these types of structural changes was unexpected, but it explained the symptoms that the patient suffered from. While we know colored vision disturbance is a well-described side effect of this medication, we have never been able to visualize the structural effect of the drug on the retina until now,” said Rosen said.

“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,” he added.

Since the drug was purchased online, researchers couldn’t rule out the possibility that a contaminant might have also contributed to the condition.

Other side-effects of the medication when used too heavily include dizziness, sudden hearing loss and painfully long-lasting erections that could even cause permanent damage to penis if left untreated.