Joel Hunter, MD Refractive Surgeon, Hunter Vision Updated 10/31/18 12:38 PM
Surgery on your eyes is painless. “But that wasn’t the question!” you might be shouting angrily at the screen. Or maybe you’re less of a shouter and just wondering what painless surgery has to do with dry eyes. It’s probably the second one, honestly. Anyone with enough rage to shout at an online article is probably out picketing rather than reading this. And that’s sad because they’ll miss how painless surgery and dry eyes are actually connected.
It’s all about nerves.
The same feature that makes your eye so incredibly sensitive also makes your eye incredibly easy to anesthetize (numb). Namely, very superficial, very thin, unmyelinated (naked) nerves have pathways all throughout your cornea They originate from larger nerves behind the eye, and are the final thinnest, most distributed end points of those nerves. Only the largest of them are able to be seen with the microscopes we use in clinic.
That means those nerves are able to be made completely, 100%, no-exceptions, numb from just an eye drop. The drop absorbs into the cornea and those nerves are left completely asleep. Then the drop wears off and all is back to the way it was before, no harm no foul. Very fine nerves means very high sensitivity, but because they are all right there by the surface, it also means they are incredibly easy to numb.
Full sensation takes time to come back.
LASIK is very minimally invasive (it involves a depth of just around 100 micrometers — about the thickness of a human hair), but those nerves are so fine and so numerous, that LASIK will still involve some of them. Those little branches of nerves that were in the area that was treated will have deficits in sensation until they go back to the way they were. Sometimes that’s a couple of months later.
To clarify, this doesn’t mean that someone has a numb eye for a long time after LASIK. If you get an eyelash in your eye, you’ll still be very uncomfortably aware of it. But it does mean we expect a temporary compromising of the finer circuitry involved in monitoring tear film levels. Your eye is always monitoring how the layer of tears on its surface is doing. Is there enough aqueous layer? Is the salt content too high? Should I pour gallons of tears now because I’m watching the surprise super sad beginning of the movie “Up”? All the while, we remain blissfully unaware that our corneal nerves are putting in such tedious hours of tear film monitoring.
Your eyes may be dry but not feel dry.
Until the monitoring and regulation of that tear film is compromised, then we can tell. What’s interesting about the first two months after LASIK is that most people don’t know that their eyes are dry. The only symptoms they have is fluctuations in the quality of their 20/20 vision. Almost daily, I’ll tell someone their eyes are a little dry at a one month post op appointment, and they’ll say, “They aren’t dry. I just have fluctuations in my vision. They don’t feel dry.” Like they are playing a game of two truths and a lie. The reason this happens is that dryness in the first eight weeks usually just causes vision fluctuations, but doesn’t feel like dryness. Guess why? It’s because the nerves aren’t good at monitoring dryness yet. Tada! Isn’t that neat how it all wraps up into a self-referential explanation?! I think it is.
The good news in all this is that LASIK is really minimally invasive so it is really uncommon to have levels of dryness that cause problems beyond minor occasional annoyance for the first few months. After that, the circuitry is back up and running like its old self, and we don’t have to worry about the dryness anymore.
Are there cases where dryness lasts longer?
Yes. Yes there are. We can almost always, however, see risk factors for those cases ahead of time. And because the treatments are so good these days, it is pretty common that LASIK is still a perfectly viable option. We just become better friends in those cases, because it takes a few extra visits to go from “dry eyes” to the upgraded version, which is “eyes.” And that’s not so bad! Everybody likes having new friends.