Popular erectile dysfunction drug linked to eye disease that can cause irreversible vision loss

An international team of researchers analyzed health records from nearly 74,000 men ages 40 and older with lower urinary tract symptoms to examine whether long-term tadalafil use was associated with a greater risk of glaucoma. 

The study, published in the British Journal of Ophthalmology, compared about 37,000 men prescribed tadalafil with a similar group who did not use phosphodiesterase type 5 inhibitors, the drug class that includes Cialis.

Men who used tadalafil were 22% more likely to develop glaucoma than those who did not use the drugs, according to the findings.

Dr. Valerie Kattouf, an optometrist at the Illinois Eye Institute who was not involved in the study, told Fox News Digital that glaucoma can be difficult to notice in its early stages.

"Glaucoma is an eye condition that especially in its early stages often does not present with visual symptoms," Kattouf said.

As glaucoma progresses, people may gradually lose their side, or peripheral, vision, she said.

Kattouf said people with a family history of glaucoma, high pressure inside the eye or severe nearsightedness may face a higher risk. Those who take Cialis daily over a long period of time may also warrant closer monitoring, she said.

People who regularly use the medication should have a comprehensive eye exam to establish a baseline for their eye health, according to Kattouf. Doctors can check pressure inside the eyes and perform other tests to look for changes that could signal glaucoma.

The researchers noted several limitations to the study.

Researchers also could not account for changes in medication use or other health conditions that developed over time.

Fox News Digital reached out to Eli Lilly, the manufacturer of Cialis, and the study's researchers for comment.