Already under scrutiny over concerns that Viagra could cause melanoma a new study suggests that that Viagra can cause vision problems.

Australian researchers published an article in Science Direct about a study using animal trials to explore the effects of Viagra. The researchers found that mice exposed to Viagra suffered  changes in the way their retinas worked.

Researchers explored the biochemical pathways. One key element of the study was that that these effects were dose dependent. That means the reported effects showed up more strongly with higher doses of the drug. Researchers often consider dose-dependence a strong indicator that results of a study indicate a real connection between a cause and effect.

However, visual problems aren’t the only issue facing Pfizer over Viagra. According to a 2014 study published in JAMA Internal Medicine, a publication by the American Medical Association, patients taking Viagra suffered from an 84 percent increase in their risk of developing melanoma.

In the JAMA Internal Medicine study, researchers used public health data collected over the course of 10 years from almost 26,000 men. Researchers used a variety of statistical tests to measure the strength of the correlation between Viagra and melanoma, as well to as test several other possibilities.

Researchers did not find a similar link between melanoma and erectile dysfunction, nor a link between other types of skin cancer and Viagra. This specificity lends credence to the idea that there was a link between Viagra and melanoma.

Melanoma is a particularly deadly form of skin cancer. It spreads more aggressively than other forms of skin cancer.

With all cancer, it is easier to treat early, but once the cancer spreads beyond the initial site, it becomes much harder to treat. Many types of skin cancer are closely linked to the UV radiation in sunlight. Repeated sunburns and tanning may increase the risk of various skin cancers like melanoma.

However, studies like the JAMA Internal Medicine study have begun to draw attention to the fact that drugs may be among the causes of skin cancer, including Viagra and related drugs. The JAMA Internal Medicine study speculated that Viagra may interfere with the production of chemicals cells produce to help keep cancer cells in check. The body uses such compounds because cells often malfunction. Most of the time, these chemicals can destroy cancer cells before they become a problem.

A class action lawsuit investigation has been launched to explore the possibility of legal action over the alleged link between Viagra and melanoma. Similar lawsuits in the past have alleged that drug makers like Pfizer were aware of risks associated with their drugs, but sold the drugs anyway, endangering the public.