Viagra and Cialis have been around long enough that we know a lot about them.

Then every once in a while, a study comes along that makes us look again.

This year, two large studies examined PDE5 inhibitors, the family of medications that includes sildenafil (Viagra) and tadalafil (Cialis), and the risk of glaucoma.

Here’s the interesting part.

They didn’t agree.

One study, looking at men using these medications for erectile dysfunction, found a lower chance of developing glaucoma.

Another, looking at men taking daily tadalafil for urinary symptoms from an enlarged prostate, found a higher chance over five years.

So which is it?

At this point, we don’t know.

And that’s probably the most important part of the story.

Both studies were observational. Researchers looked at large groups of patients and found an association.

That’s useful, but it doesn’t prove that Viagra or Cialis either protects your eyes or harms them.

There were also important differences between the studies. The men were taking the drugs for different reasons.

One group was using PDE5 inhibitors for erectile dysfunction, often intermittently, while the other involved daily tadalafil for urinary symptoms. The populations and follow-up were different as well.

Those differences may matter.

Or they may not.

This is one of those moments in medicine when a headline can get considerably ahead of what the science actually tells us.

If you’re taking sildenafil or tadalafil, I wouldn’t stop because of these studies.

I also wouldn’t start taking Viagra because you heard it might prevent glaucoma.

We aren’t there.

What I would do is pay attention.

Glaucoma can gradually damage the optic nerve and may cause permanent vision loss. Early disease often produces no symptoms, which is one reason routine eye examinations matter, particularly if you already have glaucoma, elevated eye pressure, a family history or other risk factors.

And if you’re taking one of these medications, make sure the physician prescribing it knows about your eye history.

For someone like me who has prescribed PDE5 inhibitors for years, these studies are interesting precisely because they conflict.

Maybe daily exposure matters.

Maybe the populations were different in ways we don’t fully understand.

Maybe one or both associations will become less impressive as better studies are done.

That’s how medicine works sometimes.

Two studies can look at roughly the same question and point in opposite directions. The answer isn’t to pick the one you like better.

It’s to wait for better evidence.

For now, Viagra and Cialis remain useful medications for the patients who need them.

As for whether they’re helping or hurting your glaucoma risk?

That’s one I’m not ready to put on the prescription label just yet.