Joel Hunter, MD Refractive Surgeon, Hunter Vision Updated 07/31/17 7:31 AM
There are two different ways to look at this question. With admitted bias, I would label those two ways the “wrong way” and the “right way.” I’ll get into those in a moment, but first, it may be helpful to lay some groundwork on why distance and near vision are on opposite teams after age 40 or so.
Once your eye loses the ability to autofocus, it becomes very much like a fixed-focus camera. “What’s that?” you may say, and for good reason. No one sells fixed focus cameras because they are useless. If you could find one, you’d see that your camera can only take one kind of photo. Depending on the model you’ve found you may find you can only take photos exclusively of objects beyond 20 feet away. If you use that camera to snap a photo of a document you’re holding, it going to look like an indistinct, square ghost. If you’ve got the other model, then your camera can only take good photos of objects close at hand. Anything beyond a few feet will just look like a Monet painting.
Now, with that established, on to the “wrong way” to view this question of whether it’s possible to get your near vision fixed without losing your distance vision. If you assign your vision with only the capability of those cameras—where every improvement at near means a functional decrease at distance—the premise is wrong. It isn’t surprising this view is held by most people, because it can be confirmed by anyone who has worn reading glasses. If you’ve ever tried to look up at the TV through your reading glasses, you see it firsthand. Those glasses, which are a lifesaver for reading, turn the TV into a mess of glowing, colored patterns. Your fixed-focus camera, in this case, is the model that only works for near. It makes sense for everyone with this starting point to approach the distance vs. near vision correction question with caution. Here’s the problem: the difference between a cautious approach and a skeptical approach is often based on how you’re feeling that day. And that’s a shame, because skepticism on this topic keeps a lot of people wearing reading glasses or bifocals when they don’t have to. The reason I label the “wrong way” to look at this question as “wrong” is that it’s usually wrong. To see why it’s wrong requires us to consider the other, more helpful mindset about how to approach fixing near vision without losing distance vision.
Your visual system, starting at the front of your eye and finishing at the visual cortex on the back of your brain, is indescribably more complicated than our camera analogy in the previous paragraph. It’s also more capable. While your eyes are very much like fixed-focus cameras after age 40, your visual system is a wholly different conversation. You’ve got two eyes acting like open gateways of visual information and an entire lobe of your brain to process it all.
Very few people, whether naturally or with glasses, have the exact same visual acuity in both eyes when tested under standardized conditions. Sometimes they are 20/15 (excellent) in one eye and 20/20 (very good) in the other eye. Sometimes it is more noticeable and they’re 20/15 in one eye and 20/25 (okay-ish) in the other eye. The interesting thing is this: it’s almost always noticeable to them only during testing, when covering one eye and then the other. It turns out, your visual cortex—tasked with processing all this light coming into your eyes and creating what you actually see—doesn’t care if both eyes are identical. It does, however, care very much if it can use both eyes at the same time. Therefore, those two fictional patients I just wrote about will test the same with both eyes open. But if we pretend the second guy has one eye at 20/15 and the other eye at 20/100 (horrible), now he’s going to lose when they test their vision with both eyes open. In one case, the visual cortex processing the vision has two eyes to work with. In the other, it only has one eye to work with.
If you made it through the unendurable tedium of that paragraph, you deserve an award. The reason all that matters is because it opens a way for us to game the system and get both distance and near vision. In that example, 20/25 in one eye didn’t pose a problem for the brain to use both eyes at the same time. What about a little worse than 20/25 in one eye? What about a little worse still? As luck would have it, the answer is good news for the vast majority of people over age 40. The amount of near vision in one eye required to read creates a level of blur in the distance in that eye that is still mild enough for your visual cortex to use both eyes. It is able to blend the vision between the two eyes (which is where the term “blended vision” comes from) to allow distance and near vision. This is why people who despised monovision contacts can still be great candidates for blended vision. In those cases, they couldn’t use both eyes because the difference was too great. But once the eyes are accurately set to work together, all is well.
So can you gain near vision without losing distance vision? If we are talking about cameras, or eyes as individual units, then the mathematics of optics confirm the answer is no. But I believe that’s the wrong way to look at that question. If we turn the conversation to your visual system and all it’s capable of, the options open up quite a bit. Can you gain near vision and keep distance vision when you make the whole system work together as more than the sum of its parts? There are lots of folks who’ve had LASIK or Refractive Lens Exchange or cataract surgery who would say “yes!” to that question.