July 9, 2022 | Keratoconus

Does Cross Linking Hurt At All?

By Barrett Eubanks, M.D.

Does Cross Linking Hurt At All?

Nobody likes getting scratched in the eye. But that is sorta what happens during eye surgery (in a much more controlled manner). Corneal cross linking to treat keratoconus is no exception. But thankfully, while scary and intimidating, you don’t have to worry about any pain during the procedure.

Corneal cross linking is actually a pain free procedure. Despite all the treatment being done to the cornea, numbing eye drops are very effective at eliminating pain. But it is still possible to have some discomfort from the eyelid holder during the procedure. And the recovery after corneal cross linking will have some pain.

So let’s cover what you can actually expect during the procedure and why this all happens (or doesn’t happen in the case of pain).

Brief Overview of Corneal Cross Linking

For an in depth look at the procedure, check out The Complete Walk-through of the Corneal Cross Linking Procedure

Corneal cross linking works by first applying a special medication with riboflavin and then applying UV light. The UV light interacts with the riboflavin to create strong bonds within the cornea - making the cornea less weak.

There are actually multiple ways to perform corneal cross linking. The method which is approved for use in the United States is the “epi-off" method of corneal cross linking. This in contrast to the “epi-on" method. The difference can be readily explained just from the name itself.

On the very surface of the cornea is a thin layer of cells called epithelium (or epi for short). One way to perform corneal cross linking is to remove the epithelium. ie take the epi off…Removing the epithelium can allow for better absorption of the riboflavin and more penetration of the UV light. This equals better results.

But here’s the thing. The cornea is the most sensitive structure in our body. You can’t even touch your cornea without it being uncomfortable. Even worse, the part of the cornea underneath the epithelium is even more sensitive and painful when exposed.

So how is even remotely possible this epithelium can be removed without any pain at all?

Topical Anesthetic Eye Drops

The answer is because of topical anesthetic eye drops or numbing drops. Tetracaine or proparacaine are two commonly used numbing eye drops. And they work very very well.

What the medication proparacaine actually looks like - on a molecular level
What the medication proparacaine actually looks like - on a molecular level; Anypodetos, Public domain, via Wikimedia Commons

Initially it will burn when these eye drops are placed within the eye. This burning sensation lasts approximately 5 to 15 seconds. But once this burning sensation wears off, the eyes are numb. The eyes may feel a little “heavy" at this point. You could touch your eye and not feel a thing (but please don’t; very easy way to scratch your eye).

When the eyes are numb, you won’t have any pain on the cornea. The epithelium can be removed and the corneal cross linking procedure can be completed while you remain comfortable. You may still feel a few other sensations (such as a pressure sensation or cool water sensation), but you won’t feel actual pain.

However, these numbing eye drops only last approximately 20 minutes before slowly wearing off. Because corneal cross linking can take a little over an hour, you continue to receive these drops throughout the whole procedure to be sure your eye stays numb.

But There Can Be A Reason For Pain

Not from the eye, but there are other ways you can have some pain during corneal cross linking. The biggest culprit is the eyelid holder used to prevent you from blinking.

This eyelid holder is placed underneath your eyelids and expanded to keep the eyelids off the cornea for the treatment.

But some people can have really tight eyelids. This creates lots of pressure as the eyelid holder is expanded. This pressure can occasionally create some discomfort as well. (and it will especially be uncomfortable and painful if you squeeze your eyelids down on the eyelid holder). Relaxing and opening both eyes will help with that “eyelid squeeze reflex." Over the course of the procedure, you may even find your eyelids start to relax naturally on their own easing up some on this eyelid holder.

This eyelid holder can also at times press up against the bony orbit that surrounds our eyes. Because these eyelid holders are made of metal, you have the sensation of metal pushing against bone. Also not comfortable. This eyelid holder can often be adjusted if you do develop this discomfort so let your surgeon know if this happens.

Once this eyelid holder sits comfortable underneath your eyelids, you may even well forget that its even there through the course of the procedure; making corneal cross linking very comfortable and easy to go through.

But Then The Recovery

The real pain after corneal cross linking comes with the recovery.

That epithelium that was removed during the procedure must regrow. Until that epithelium regrows, the part of the cornea underneath the epithelium, the super sensitive stroma, is exposed. This causes pain.

However, most people who go through corneal cross linking aren’t in extreme pain. This is because the pain during the recovery afterwards is blunted by adding a soft contact lens on the eye. This contact lenses serves as an artificial barrier until our own natural epithelium barrier can regrow. This contact lens drops the pain from being bad down to being a mild to moderate ache or scratchiness.

Some people may notice almost no pain at all with this contact lens in place. For others, however, this contact may move around a little and cause a bit more pain. Overall the discomfort during this recovery can be variable.

But it only takes about 3-4 days for the epithelium to complete its covering of the cornea. The pain drops and the eye returns back to normal.

See also What To Know For The Corneal Cross Linking Recovery


Topical anesthetic eye drops or numbing drops take care of all pain during corneal cross linking. Occasionally though, the eyelid holder used during the procedure can cause some discomfort. Once you make it though the procedure, though, expect to have some pain or discomfort until everything heals up.

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