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EpiOn EpiOFF CrossLinking


Is there any evidence that Riboflavin-soaked epithelium (or just plain old intact epithelium) blocks UV A to the stroma?

Dr. P


Why are so many people so averse to removing epithelium for CXL? Is this a religious prohibition or something?;)

I remember assisting retina surgeons at Harvard/MEEI (including my uncle) and they’d remove epithelium at the slightest excuse for a better view. There are PRK and ASA surgeons out there who are doing this thousands of times each and every year without delayed healing, pain, or scarring

So I’d like a response from the surgeons who are trying so hard to make epi-on CXL approach the proven efficacy of epi-off CXL, why they’re so averse to removing epithelium, when with a clean en-bloc epithelial removal, a proper BCL, and the right postop meds, there’s no pain and almost zero risk of infection?

I’d like to restate a query nobody responded to:

Why spend so much effort on such a limited application (CXL) when if all of us spent that time optimizing epithelial regrowth, that’d be more useful in a number of eye surgeries literally 100,000x as numerous?—

Emil William Chynn, MD, FACS, MBA



If the outcomes are the same – what is the advantage of removing the Epithelium with CXL?

In our study – when patients have Epi-On CXL

1. Patients are able to return to work 1-2 days after their procedure

2. The risk of infection is exceptionally low.

3. One of the risks with Epi-Off CXL is corneal haze – and this risk is dramatically reduced with Epi-ON

4. Patients do not need a bandage contact lens

5. Patients can return to their RGP, scleral or soft toric contact lenses 2-3 days after their procedure

6. There are fewer office visits.   After the 1 day postop visit, there is no need for a second visit – other than to monitor changes.  So in our protocol, we have patients return at 3 months.  With Epi-Off – patients would need a visit a 5 days postop to confirm that their epithelium has healed.  These are steep corneas, so epi healing can take longer in some patients, requiring additional visits

7. Less steroids are needed with Epi-ON – since the risk of haze is dramatically lower than with Epi-Off

These are just a few advantages.   Again – in our study, when confirming there is sufficient riboflavin in the corneal stroma prior to UV light administration, we have had excellent results.

Best regards




That’s a big if Billy

If you look at 100 CXL studies in both the worldwide peer and non-peer reviewed literature

You’d probably see something like this:

66 studies showing epi-off more effective

34 studies showing epi-on equally effective

0 studies showing epi-on more effective

Which raises the following very important question that I believe has actually never been voiced or addressed:

If epi-on is truly equally effective, wouldn’t normal statistical variation mean that there should be at least ONE study showing it’s MORE effective?

To make my query more intuitive, consider the following example:

Antibiotic A and B are in reality equally effective

100 doctors around the world compare them in 100 studies both formal and informal

The result would never look like this:

66 studies showing A more effective

34 studies showing B equally effective

0 studies showing B more effective

If this WERE the result, would anyone then conclude that A and B are equally effective? Of course not!

We’d all conclude that A is obviously (at least somewhat) more effective than B

You’d need a n of like 1000 eyes in each arm of your study, Billy, to convince me that epi-on is equally effective as epi-off. Obviously that’s not possible

So think of the above “thought experiment” as a “virtual meta-analysis” oh wise fellow Kera-netters, and tell me if my logic is solid or not??

Emil William Chynn, MD, FACS, MBA


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