Dual-system microbiological screening to prevent fungal transmission in corneal grafts: a four-year eye bank retrospective study

Imagine your body is a bustling city, and your eyes are the most important windows in town. Sometimes, those windows get so cloudy or damaged that you can't see the world clearly anymore. To fix this, doctors can perform a delicate surgery called a corneal transplant, where they swap out the damaged window for a fresh, clear one from a donor. But here's the catch: just like a new window pane needs to be spotless before it's installed, the donor tissue must be completely free of invisible invaders like bacteria and fungi. If even a tiny, sneaky germ is hiding on the new cornea, it can grow into a serious infection once it's inside the eye, potentially ruining the surgery and causing pain or blindness. This is why eye banks act like high-tech security checkpoints, screening every single piece of tissue to make sure it's safe. The big question scientists have been asking is: "How can we build the ultimate security system to catch these invisible stowaways before they ever reach the patient?"

This paper tells the story of a team in Italy who decided to upgrade their security system to a "dual-screen" mode to stop fungal infections, specifically a type of yeast called Candida. Think of their old method as checking a package with just one metal detector. Their new method uses two different kinds of detectors working together: one that looks for cloudy growth in a liquid (like seeing fog form in a jar) and another that listens for tiny chemical signals (like a super-sensitive microphone hearing a whisper). They tested this new system on thousands of corneas over four years. The results were incredibly promising: while they found many contaminated corneas and safely threw them away, zero patients who received a transplant got a fungal infection. The study also figured out that younger donors, summer months, and waiting too long after death before collecting the cornea made the tissue more likely to be dirty. They even developed a smart strategy for the "twin" cornea (the other eye from the same donor) when one eye was found to be contaminated, deciding carefully whether to save it or toss it based on extra tests.

The Story of the Super-Security Eye Bank

In the Emilia-Romagna region of Italy, the Eye Bank is like a busy warehouse that stores and prepares clear, healthy windows (corneas) for people who need them. For years, they used a method called "organ culture," which keeps the corneas alive in a warm, cozy incubator (around 31–37°C) for up to 30 days. This is different from the "cold storage" used in some other places, which is like putting the corneas in a fridge. The warm method is great because it keeps the cells happy and allows scientists to run tests over a longer period, but it also means that if a germ is there, it might grow faster.

To make sure no germs sneak through, the team introduced a dual-system screening. Imagine you are checking a suitcase for forbidden items.

1. The Turbidimetric System (The Fog Detector): This system uses a machine that shines light through the liquid the cornea is soaking in. If bacteria or fungi are growing, the liquid gets cloudy (turbid), just like milk mixing into water. The machine measures this cloudiness to spot trouble.
2. The Fluorimetric System (The Chemical Whisperer): This machine is even more sensitive. It listens for carbon dioxide (CO₂), a gas that living germs breathe out. It checks the liquid every 10 minutes for a whole week. If the germs are there, they "whisper" CO₂, and the machine catches it.

The Great Hunt for Candida

The researchers looked back at data from 2020 to 2023. During this time, they processed 3,138 donor corneas and used 2,255 of them for transplants.

The Big Win:
Under this new, super-rigorous protocol, zero patients developed a fungal infection (like Candida keratitis or endophthalmitis) after their surgery. Before this new system was fully in place, there had been 5 cases of Candida complications in just 5 transplants. The new system stopped all of them.

The "Bad News" That Was Actually Good News:
The screening was so good that it caught a lot of trouble before it could reach a patient. Out of the 3,138 donations, 204 (about 6.5%) were found to be contaminated with bacteria or fungi.

• 136 of those were specifically infected with Candida.
• Because they caught these, these corneas were safely discarded and never used.
• This means the patients who did get a transplant got a clean, safe window.

Who and What Makes Corneas "Dirty"?

The team didn't just stop at catching the germs; they wanted to know why some corneas were dirty and others were clean. They played detective with the donor's history and found some clear patterns:

• The Age Factor: Younger donors were more likely to have contaminated corneas. The average age of a "dirty" donor was 65 years, while "clean" donors averaged 68 years. It seems younger tissues might be more active, giving germs a better place to hide or grow.
• The Seasonal Sneak: Summer was the most dangerous time. Corneas donated in the summer were twice as likely to be contaminated compared to winter. The heat and humidity probably help germs multiply faster.
• The Waiting Game: The longer you wait after a person dies to collect the cornea, the riskier it gets. If the collection happened 12–24 hours after death, the risk of contamination went up significantly compared to collecting within 6 hours.
• The Hospital Ward: Donors who died in Internal Medicine or Oncology (cancer) wards were more likely to have contaminated corneas than those who died in the ICU. This might be because these patients had been in the hospital longer or had different medical histories.

The Mystery of the "Mate" Cornea

Here is a tricky part of the story. When a donor gives two eyes, they are called "mate corneas." If one eye tests positive for germs, what do you do with the other one? Do you throw both away, or can you save the second one?

The study looked at 191 cases where one eye was contaminated.

• 62.3% of the "mate" corneas had to be thrown away.
• The main reasons were: confirmed contamination (it was dirty too), altered shape (it looked damaged), or the donor wasn't suitable for other reasons.
• However, the new protocol allowed them to do extra tests on the "mate" cornea. If the first eye was positive, they didn't just guess; they tested the second eye again after 14 days. This extra step helped them make a safe decision: sometimes they could save the second eye, but mostly, they had to be very careful and discard it to be safe.

What This All Means

This paper shows that by using two different high-tech detectors and being very strict about when and how they test, eye banks can stop fungal infections completely. It suggests that:

1. Younger donors and summer donations need extra attention.
2. Waiting too long to collect the cornea is a big risk.
3. Discarding the "mate" cornea is often the safest choice, but with extra testing, we might be able to save some without risking the patient.

The authors are very confident that their new system works because they saw zero infections in over 2,000 surgeries. While they can't say for sure that only their method caused this (since they didn't run a fake experiment to compare), the drop from 5 infections to 0 is a very strong sign that their "dual-screen" security is doing its job. It's a reminder that in the world of eye transplants, being a little paranoid about germs is the best way to keep people seeing clearly.