SYDNEY, Australia – The blue pill is under scrutiny because it can cause unusual, detrimental visual responses for users who carry a common mutation for eye disease.

According to a study to be published in the journal Experimental Eye Research in November, sildenafil, the active ingredient in the erectile dysfunction drug, Viagra, can inhibit an enzyme important for transmitting light signals from the retina to the brain, even in otherwise healthy people.

“Side effects can include sensitivity to bright light, blurred vision and altered color vision,” says Dr. Lisa Nivison-Smith, of Australia’s University of New South Wales School of Optometry and Vision Science and one of the leaders of the study.

“We are concerned that people who have normal vision but who carry a single copy of the mutant gene for the blinding disease, Retinitis Pigmentosa, could be more susceptible to these changes.”

The study was conducted using mice and found that the animals had a transient vision loss after being fed sildenafil that was heightened and lasted longer in mice with the mutation.

Also found were early signs of cell death in the eyes of carrier mice, but not in normal mice, suggesting that sildenafil may cause degeneration in carriers of retinal disease.

“These findings are highly significant because about one in 50 people are likely to be carriers of recessive genes which cause retinal disease but are unlikely to know this, because their vision is normal,” Nivison-Smith said.

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