ATLANTA (CBS Atlanta) – An ingredient used to make Viagra has been found to trigger unusual visual problems for some patients, according to a new study.

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

The New Zealand researchers discovered than an active ingredient called sildenafil can inhibit an enzyme which is important for transmitting light signals from the retina to the brain.

Patients who carry a common genetic mutation for eye disease are the most likely to develop problems.

“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,” stated Nivison-Smith. “These finding 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.”

The scientists gave a single dose of sildenafil to normal mice and to mice with a single copy of the mutant gene.

They found the normal mice suffered visual problems for a short time while the mice with the mutation showed heightened visual problems that lasted much longer.

They also found early signs of cell death in the eyes of the genetic mutation mice, but not in the normal mice, suggesting sildenafil may cause degeneration in carriers of retinal disease.

“A better understanding of the effect of this family of erectile dysfunction drugs could help scientists and clinicians plan more successful strategies to account for factors such as a patient’s medication and genetic makeup in diseases which cause blindness,” urged Dr Nivison-Smith.

The study is published in the journal Experimental Eye Research.

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