Common eye ointments damage glaucoma implants used in 60 countries

A surgeon in Japan noticed something troubling during surgery: a glaucoma implant that should have been flexible and resilient had swollen so much it ruptured. That observation led to research that's now warning doctors worldwide about a simple but serious problem — the petrolatum-based eye ointments used after many surgeries can destroy the tiny devices meant to help patients see better.

Glaucoma affects about 76 million people worldwide. The condition damages the optic nerve when fluid builds up inside the eye and doesn't drain properly, eventually stealing vision if left untreated. For decades, surgery was the main option, but it often came with complications. The PRESERFLO MicroShunt changed that. It's a thumbnail-sized filtration device that surgeons place in the eye to help fluid drain more effectively. It's gentler than traditional surgery, causes fewer complications afterward, and reduces how many medications patients need.

But there's a catch — one that the manufacturer has always warned about, though not always loudly enough.

The material works too well

The MicroShunt is made from a specialized plastic polymer chosen precisely because it's flexible, compatible with eye tissue, and unlikely to trigger scarring or inflammation. Those same qualities, though, make it vulnerable to oil. The polymer essentially sucks up petrolatum the way a sponge absorbs water.

When this happens, the implant swells. Its shape changes. Its flexibility disappears. During surgery, it can rupture entirely.

Researchers at Nagoya University in Japan decided to investigate how serious this actually was. They reviewed seven patients whose MicroShunts had been removed, then ran laboratory tests to see what happened when they exposed unused implants to petrolatum-based ointment.

The results were striking. Within 24 hours, the implant's outer diameter had swollen to 1.44 times its original size. The fin-like section expanded to 1.29 times its original width. After three months in ointment, oil made up 73% of the implant's total weight — it had essentially absorbed the ointment like a sponge.

In the patient cases, the pattern was clear: three patients whose exposed implants were treated with petrolatum ointment all showed swelling, and two of those ruptured. Three patients whose implants stayed covered by eye tissue and received no ointment showed no damage. One patient with an exposed implant who didn't receive ointment had no swelling either. The message was unmistakable — direct contact with the ointment, not exposure to air, was the culprit.

What happens next

The researchers published their findings in Graefe's Archive for Clinical and Experimental Ophthalmology and are urging clinicians to stop using petrolatum-based ointments in patients with MicroShunt implants — especially when the device is exposed. They're calling for alternative post-surgery treatments and for more research to understand whether swelling damages the implant's function even when it doesn't rupture.

The manufacturer has always specified this warning in the official instructions. The real problem is that the warning hasn't filtered down to everyday clinical practice. Doctors prescribe what they've always prescribed. Patients use what they're given. No one connects the ointment to the implant failure until something goes wrong.

This is the kind of finding that changes nothing overnight but slowly reshapes how medicine is practiced. In glaucoma clinics around the world, a small shift is beginning — a reminder that even well-established materials can cause unexpected harm when their chemical properties aren't fully understood or communicated.