Everyone will lose or have already lost something we rely on every single day. I am, of course, talking about keys. What I want to talk about is one of the most important minds: vision.
Every single day we each lose a little bit of our ability to refocus our eyes until we can’t refocus at all. We call this condition presbyopia, and it affects two billion people worldwide. It’s the reason why people wear reading glasses or bifocal lenses. I’ll get started by describing the loss in refocusing ability leading up to presbyopia.
As a newborn, you would have been able to focus as close as six and a half centimeters, if you wished to. By your mid-20s, you have about half of that focusing power left. Ten centimeters or so, but close enough that you never notice the difference. By your late 40s, though, the closest you can focus is about 25 centimeters, maybe even farther. Losses in focusing ability beyond this point start affecting near-vision tasks like reading, and by the time you reach age 60, nothing within a meter radius of you is clear.
That sounds a bit troubling. I want to remind you that presbyopia has been with us for all of human history, and we’ve done a lot of different things to try and fix it. So to start, let’s imagine that you’re sitting at a desk, reading. If you were presbyopic, it might look a little something like this. Anything close by, like the magazine, will be blurry.
Moving on to solutions. First, reading glasses. These have lenses with a single focal power tuned so that near objects come into focus. But distant objects necessarily go out of focus, meaning you have to constantly switch back and forth between wearing and not wearing them. To solve this problem, Benjamin Franklin invented what he called
“double spectacles.”
Today we call those bifocals, and what they let him do was see far when he looked up and see near when he looked down. Today we also have progressive lenses that get rid of the line by smoothly varying the focal power from top to bottom.
The downside to both is that you lose the field of vision. At any given distance because it gets split up from top to bottom like this. To see why that’s a problem, imagine that you’re climbing down a ladder or stairs. You look down to get your footing, but it’s blurry. Why would it be blurry? You look down, and that’s the near part of the lens, but the next step was past arm’s reach, which for your eyes counts as far.
The next solution I want to point out is a little less common but comes up in contact lenses or LASIK surgeries, and it’s called monovision. It works by setting up the dominant eye to focus far and the other eye to focus near. Your brain does the work of intelligently putting together the sharpest parts from each eye’s view. Still, the two eyes see slightly different things, making it harder to judge distances binocularly.
So, where does that leave us? We’ve come up with a lot of solutions, but none of them quite restore natural refocusing. None of them let you look at something and expect it to be in focus.
But why? To explain that we’ll want to take a look at the human eye. The part of the eye that allows us to refocus on different distances is called the crystalline lens. Muscles are surrounding the lens that can deform it into different shapes, which changes its focusing power. What happens when someone becomes presbyopic? It turns out that the crystalline lens stiffens to the point that it doesn’t change shape anymore.
Thinking back on all the solutions I listed earlier, we can see that they all have something in common with the others but not with our eyes, and that is that they’re all static. It’s like the optical equivalent of a pirate with a peg leg. What is the optical equivalent of a modern prosthetic leg? The last several decades have seen the creation and rapid development of
focus-tunable lenses.
There are several different types. Mechanically-shifted Alvarez lenses, deformable liquid lenses and electronically-switched, liquid crystal lenses. Now, these have their trade-offs, but what they don’t skimp on is the visual experience. The lenses we need already exist. Problem solved, right?
Not so fast. Focus-tunable lenses add a bit of complexity to the equation. The lenses don’t have any way of knowing what distance they should be focused on. We need glasses that, when you’re looking far, far objects are sharp, and when you look near, near objects come into focus in your field of view, without you having to think about it.
A develper group try in Stanford to build that exact intelligence around the lenses. The prototype from virtual and augmented reality systems to estimate focusing distance. They have an eye tracker that can tell what direction our eyes are focused on. Using two of these, it is possible to triangulate the direction to get a focus estimate. Just in case, though, to increase reliability, does it also added a distance sensor. The sensor is a camera that looks out at the world and reports distances to objects.
The next step was to test the device on actual people. So there was recruited about 100 presbyopes and had them test the device while we measured their performance. What they saw convinced right then that autofocus was the future. The participants could focus more quickly, and they thought it was an easier and better focusing experience than their current correction.
Put it, and autofocus doesn’t compromise like static corrections in use today when it comes to vision. There’s a lot of work. For example, the glasses are a bit bulky. And one reason for this is that it used bulkier components that are often intended for research or industrial use. Another is that they need to strap everything down because current eye-tracking algorithms don’t have the robustness that are request.
So moving forward, to make future autofocus eventually look a little bit more like normal glasses. So it’s only a matter of time. It’s pretty clear that shortly, instead of worrying about which pair of glasses to use and when we’ll focus on the important things.
