Monofocal IOLs Part Two: Distance and Near Vision

We established in an earlier post that modern monofocal IOLs are a wonder of technology. Hubble telescope optics, without the hassle of Hubble telescope zoom – which is perfect if you want to watch your TV instead of a TV 100 miles away. So what can we do with all that clarity, conveniently focused on the world around you, rather than on galaxies lightyears away?

As it turns out, we can do quite a lot. Sure, we can get amazing distance vision and buy over-the-counter readers. But in cases where both eyes have 20/20 potential, another option opens up with monofocal IOLs. That option is blended vision, allowing for glasses-free vision at distance and near.

Blended Vision Works

Simply put, blended vision is achieved by aiming for a different prescription in the right and left eyes. But wait! If the word “monovision” jumped into your head just now, please read on – because for about 50% off folks, the thought of monovision is quickly followed by simmering rage. You remember the time you tried wearing two different contacts and couldn’t see anything anywhere and almost drove into oncoming traffic. Therefore, the rest of this blog details where monovision and blended vision differ, and why blended vision works. Even better, we’ll go over why it can work even when monovision was a mess in your case.

The goal here is to arrive at our destination (the end of this blog) with a clear picture of why monofocal IOLs make it possible to see in a way that contact lenses often cannot.

Monovision has its secret recipe right out in the open. It’s in the name. The “mono” in monovision means one – single – each eye on its own, providing the brain with its single cable input of vision. For distance, the near-focused eye must be tuned out by the brain. For near, vice versa. While some folks (around 50-70% depending on which study you read) can do this, many cannot. (Particularly people with astigmatism, but we’ll get to why that is in a moment.)

How The Brain processes visual info

In my opinion, the people that can do this are the unusual ones (i.e. the lucky ones). The human brain isn’t wired to use just one eye or the other when both eyes are open. The visual info coming in is streamed in a dual-camera way to your visual cortex. The processing isn’t a right eye / left eye event; visual information is processed spatially – as a right and left half of the vision in front of you. That means the right half of your vision is a product of the image both your right and left eye see over there.

But here’s the key point. People almost never see identically sharp in each eye. That’s true whether you need glasses or not. You can see this for yourself by covering one eye or the other. One eye is clearer, even if it isn’t the same eye every time. Our brain is wired to blend those differences in our dual camera setup. We see one clear image, created by processing two slightly different quality streams from each eye.

This key feature of how we see is what allows blended vision to work. Because it isn’t a question of whether or not we can blend the vision of a slightly different right and left eye – our brains have been doing that forever. The question is instead, how different can those images be while still allowing your brain to use and blend the vision from both eyes? For nearly everyone, the answer seems to be about 50% different – i.e. one eye sees 20/20 and the other 20/40.

Why Monovision Often Fails For Folks With Blended Vision

And here’s where we get to why monovision often fails for folks that do great with blended vision. First, having one eye at 20/100 just doesn’t work for blending. Your brain is like, “what am I supposed to do with this blur? Am I supposed to make the giant red blob stoplight meld with the clear one? Go pound sand.” (Or at least it’s the visual processing equivalent to saying it.)

Second, almost everyone has some level of astigmatism. The explanation of astigmatism is a story for another time, but for our purposes here we can just say that low to medium amounts of astigmatism are notoriously difficult to fully correct with contacts. So for a lot of people, they’re wearing contacts that give distance vision of not sharp 20/20ish to 20/25 in each eye individually. With both eyes working together, that works! However, that kind of distance vision (what I call B+ vision) doesn’t have any room to spare to add near in one eye. You’re going to need both eyes giving you their full B+ potential for it to look good.

When Monovision Works!

Which brings us to our destination! Monofocal IOLs exist to increase that potential. When A+ vision potential exists, we’re working with enough clarity of distance and near that blending becomes possible. And the type of blending we’re talking about here is a purposeful, exact difference between right and left eye. Just enough that we can read, but not so much that the brain can’t use both eyes at the same time. That means we’re still using our brain the way it wants – running its built-in software to blend the vision of our dual camera set up.

As we close, I want to confess that despite my best effort here, I’m filled with doubt that I answered every question you might have about blended vision. But maybe that’s a good thing because it gives us a good excuse to meet! A consultation has two benefits we can’t get from a blog. It gives specific answers about your eyes, and even better, it gives us a chance to talk. Dr. Shumski and I love talking about this stuff. It makes us insufferable at dinner parties, but it’s perfect at a consultation! Consultations are more fun than dinner parties anyway.

Book your free consultation online today or call us at 407-843-5665 for more information about Monofocal IOLs and Blended Vision.