A drug commonly used to treat erectile dysfunction and symptoms of an enlarged prostate may be associated with a greater risk of glaucoma, according to new research. Glaucoma is a serious eye condition that can cause gradual vision loss.

An international team of researchers examined health records from nearly 74,000 men with lower urinary tract symptoms. All of the men included in the analysis were ages 40 and older.

The researchers sought to determine whether long term use of tadalafil was associated with an increased risk of glaucoma. Tadalafil is sold as Cialis and belongs to a class of medications known as phosphodiesterase type 5 inhibitors.

The study was published in the British Journal of Ophthalmology. It compared about 37,000 men who were prescribed tadalafil with a similar group of men who did not use phosphodiesterase type 5 inhibitors.

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Researchers followed the men for up to five years. During that period, they looked for new cases of glaucoma and high pressure inside the eye, as well as whether the patients required treatment for glaucoma.

The findings showed that men who used tadalafil were 22% more likely to develop glaucoma than men who did not use the drugs. However, the observational study identified an association and did not establish that tadalafil caused glaucoma.

The tadalafil users were also 32% more likely to develop high pressure inside the eye. In addition, they were 33% more likely to develop primary open angle glaucoma, which the article identified as the most common form of the disease.

Dr. Valerie Kattouf, an optometrist at the Illinois Eye Institute, was not involved in the research. She told Fox News Digital that glaucoma can be difficult for people to recognize during its early stages.

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

As the condition advances, people may gradually lose their side vision, which is also known as peripheral vision, Kattouf said. Therefore, an evaluation may detect signs of glaucoma before a person notices visual symptoms.

"Clinical findings of glaucoma are best detected in a comprehensive vision evaluation ," Kattouf added.

Kattouf said some people may face a higher risk, including those who have a family history of glaucoma. High pressure inside the eye and severe nearsightedness may also be risk factors, according to Kattouf.

People who take Cialis daily over an extended period may warrant closer monitoring, she said. Kattouf advised regular users to receive a comprehensive eye exam that can establish a baseline for their eye health.

During an examination, doctors can measure pressure inside the eyes and conduct other tests to check for changes that could indicate glaucoma. The monitoring may be particularly relevant for patients who already have glaucoma risk factors and use tadalafil over a long period.

The researchers acknowledged several limitations to their analysis. Because the study was observational, its results showed a link between tadalafil use and glaucoma but could not prove that the medication was responsible for the condition.

Researchers were also unable to account for changes in medication use over time. Other health conditions that developed during the study period could not be accounted for either.

Despite the association identified in the health records, the researchers did not say that patients should stop using tadalafil. Instead, they said people who use the medication long term, particularly those with existing glaucoma risk factors, may benefit from regular monitoring of their eyes.

The findings place the focus on awareness and observation rather than establishing a direct cause. They also underscore Kattouf's warning that glaucoma may not produce noticeable visual symptoms during its early stages.