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Will LASIK affect my night vision?

By Joel Hunter, MD | 11/8/17 7:01 AM
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If you have night vision that you notice—enough that you clicked on an article like this to read about it—then it probably isn’t quite ideal. Folks who have excellent night vision don’t ask questions about night vision very often. I assume it’s for the same reason people don’t ask their doctor about ankle pain if their ankle feels fine. If you’ve thought about this question with LASIK, you’re there’s a decent chance you’re part of a sizeable portion of the population who doesn’t see quite as well at night. It’s like being part of a secret club with a lot of members who have no way to identify each other. Especially at night.

There are three main reasons for bad night vision, and in the right circumstances, LASIK can help. In other cases, it will have no effect. The result we try to avoid, and that we usually can avoid because of how good preoperative testing is now, is making night vision go from bad to worse. The discussion in those cases is usually more focused on why LASIK isn’t an option and what other options are available now or in the future. It’s tricky waters trying to navigate through a discussion on “how much worse would you be willing to tolerate for your night vision?” It’s better to decide against LASIK in those cases. And now, on to our three reasons for poor night vision before LASIK.

  1. You don’t need glasses during the day, but driving at night is difficult without glasses. If you’re in this boat, you’re a member of the group with annoying vision. As I’ve written elsewhere, annoying vision isn’t much of a scientific term, but I can’t stop using it as a classification because it is so accurate. Slight amounts of refractive error (need for glasses) will rob you of a little bit of distance vision and take a toll on your contrast sensitivity.

Contrast sensitivity is basically how sharp the vision looks. The interesting thing about contrast sensitivity is how heavily it relies on contrast, which is a feature of your world that varies widely depending on the situation. Noon day sunshine on a cloudless day? That’s a high contrast world you’re living in, and it’s pretty easy to see it even with eyes that don’t excel in contrast sensitivity. You don’t have to be that sensitive to contrast when there’s tons of it. But how about dusk when the contrast is low? It gets noticeably tougher. By the time it is full-blown night with dark skies, contrast is terrible and your contrast sensitivity even terribler, leaving you with vision so annoying that it creates nonsense words like terribler.

The solution to this kind of bad night vision is either glasses or LASIK. The reason glasses tend to be less popular in your category of annoying vision is the same reason no one carries an umbrella with a 10% chance of rain. Who wants to carry something around all day "just in case" it will be useful? LASIK falls firmly into the category of helping people with this kind of night vision.

  1. You wear contacts, and they work fine during the day, but at night they’re not nearly as good. Just like with annoying vision, you’re in the same boat with a lot of other folks who have the same problem. It’s the most common night vision issue I see in clinic. Members of this group usually share one unifying, yet seemingly unrelated characteristic: their night vision with glasses is beautiful compared to what it is with contacts. But get ready for the plot twist; it is a related characteristic to the cause of this kind of bad night vision! Talk about a shot out of the dark that you might have seen with glasses!

The related reason for this kind of bad night vision is either uncorrected astigmatism or because of the layer of tears necessary to keep that contact lens hydroplaning and your eye happy. Some astigmatism is slight enough that it affects the vision in low contrast situations, but can’t be fixed with toric contact lenses, which do better at higher levels of astigmatism. And for your tear layer, you can almost think of it as a bank account that you’re withdrawing from with evaporative loss all day long and by night time you’re just overdrawn. That’s why glasses work at night when contacts don’t. In this category as well, LASIK is very likely to improve the night vision to make it look as good or better than it does with glasses.

  1. Your night vision is just the pits. It’s not good with contacts, it’s not much better with glasses. You may feel like the group name of annoying vision should have been saved for your group. The good news here is there is almost never a need for a made-up name like that if you’re in this group. Almost always, there is an actual name for the problem causing this. It may be cataracts, or Fuchs’ dystrophy, or keratitis sicca, or any other of a list of impressive and mildly-frightening sounding conditions. But I have very good news. So many of these are curable, and along with the cure comes good night vision.

The most common of these by a mile is cataracts. Cataracts happen to everyone, and they never happen overnight. That means that people suffer with the symptoms of cataracts for a long time before they ever hear that they’ve got cataracts. You may have already guessed the number one symptom, and I can confirm you are right. It’s bad night vision. In this case, or for most of the other causes of bad night vision in this category, LASIK isn’t a good choice. But finding a doctor who can tell you why your night vision is bad is a great choice, because there may be a solution that makes your night vision good enough that you never think to ask about it again.

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