Mount Sinai researchers say they have shown that colour vision problems caused by retinal damage on a cellular level can result from a high dose of sildenafil citrate, an ingredient in some erectile-dysfunction medication, including Viagra and that excessive use of the drug could lead to long-term vision problems, including possible irreversible damage.

“People live by the philosophy that if a little bit is good, a lot is better. The study, published in Retinal Cases, shows how dangerous a large dose of a commonly-used medication can be,” said lead investigator Dr Richard Rosen, retinal services director at New York Eye and Ear Infirmary of Mount Sinai (NYEE).  “People who depend on coloured vision for their livelihood need to realise there could be a long-lasting impact if overindulging in this drug.”

Rosen and a team of investigators from NYEE based their study on a 31-year-old patient who arrived at an urgent care clinic complaining of red-tinted vision in both eyes that hadn’t gone away in two days. He reported that his symptoms began shortly after taking a dose of liquid sildenafil citrate that he purchased over the internet (sildenafil citrate can cause visual disturbances with normal dosage, but symptoms typically resolve within 24 hours). The patient told doctors he had consumed much more than the recommended 50mg dose, and that symptoms began shortly after ingestion. The patient was then diagnosed with persistent retinal toxicity linked to the high dose of medication damaging the outer retina. His tinted vision had not improved more than a year after his initial diagnosis, despite various treatments.

Mount Sinai researchers used state-of-the-art technology, including adaptive optics (AO) and optical coherence tomography (OCT), to examine his retina for evidence of structural damage at the cellular level.  The high-tech imaging allowed investigators to see microscopic injury to the cones of the retina, the cells which are responsible for colour vision. The damage was similar to that seen 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 coloured vision disturbance is a well-described side effect of this medication, we have never been able to visualise the structural effect of the drug on the retina until now,” said Dr. Rosen. “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.”