As you age, you gradually lose the ability to refocus your eyes — a phenomenon as old as humanity itself — leading to a reliance on bifocals, contacts and procedures like LASIK surgery. Electrical engineer Nitish Padmanaban offers a glimpse of cutting-edge tech that’s truly a sight for sore eyes: dynamic, autofocusing lenses that track your sight and adjust to what you see, both near and far.

年齢を重ねると、目の焦点を再び合わせる能力が徐々に失われ、これは人類の歴史と同じくらい古い現象であり、遠近両用眼鏡やコンタクト、レーシック手術などの処置に依存することになります。 電気技師のニティッシュ・パドマナバン氏が、目の疲れを癒す最先端のテクノロジーを垣間見せます。それは、視界を追跡し、近くと遠くの両方で見えるものに合わせて調整するダイナミックな自動焦点レンズです。

Autofocusing reading glasses of the future
スピーカー ニティッシュ・パドマナバン
アップロード 2020/06/19

「未来のオートフォーカス老眼鏡(Autofocusing reading glasses of the future)」の文字起こし

Every single one of us will lose or has already lost something we rely on every single day. I am of course talking about our keys. (Laughter) Just kidding. What I actually want to talk about is one of our most important senses: 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. That’s right, I said billion. If you haven’t heard of presbyopia, and you’re wondering, “Where are these two billion people?” here’s a hint before I get into the details. 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. 10 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.

Right now some of you are probably thinking, that sounds bad but he means you in a figurative sense, only for the people that actually end up with presbyopia. But no, when I say you, I literally mean that every single one of you will someday be presbyopic if you aren’t already. 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 far 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 which get rid of the line by smoothly varying the focal power from top to bottom. The downside to both of these is that you lose 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? Well, 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, but the two eyes see slightly different things, and that makes 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 just look at something and expect it to be in focus. But why? Well, to explain that we’ll want to take a look at the anatomy of the human eye.

The part of the eye that allows us to refocus to different distances is called the crystalline lens. There are muscles surrounding the lens that can deform it into different shapes, which in turn 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 really change shape anymore.

Now, 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 what are called “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 own trade-offs, but what they don’t skimp on is the visual experience. Full-field-of-view vision that can be sharp at any desired distance.

OK, great. 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 to. What we need are 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.

What I’ve worked on these last few years at Stanford is building that exact intelligence around the lenses. Our prototype borrows technology from virtual and augmented reality systems to estimate focusing distance. We have an eye tracker that can tell what direction our eyes are focused in. Using two of these, we can triangulate your gaze direction to get a focus estimate. Just in case though, to increase reliability, we also added a distance sensor. The sensor is a camera that looks out at the world and reports distances to objects. We can again use your gaze direction to get a distance estimate for a second time. We then fuse those two distance estimates and update the focus-tunable lens power accordingly.

The next step for us was to test our device on actual people. So we recruited about 100 presbyopes and had them test our device while we measured their performance. What we saw convinced us right then that autofocals were the future. Our participants could see more clearly, they could focus more quickly and they thought it was an easier and better focusing experience than their current correction.

To put it simply, when it comes to vision, autofocals don’t compromise like static corrections in use today do. But I don’t want to get ahead of myself. There’s a lot of work for my colleagues and me left to do. For example, our glasses are a bit — (Laughter) bulky, maybe? And one reason for this is that we used bulkier components that are often intended for research use or industrial use. Another is that we need to strap everything down because current eye-tracking algorithms don’t have the robustness that we need.

So moving forward, as we move from a research setting into a start-up, we plan to make future autofocals eventually look a little bit more like normal glasses. For this to happen, we’ll need to significantly improve the robustness of our eye-tracking solution. We’ll also need to incorporate smaller and more efficient electronics and lenses.

That said, even with our current prototype, we’ve shown that today’s focus-tunable lens technology is capable of outperforming traditional forms of static correction. So it’s only a matter of time. It’s pretty clear that in the near future, instead of worrying about which pair of glasses to use and when, we’ll be able to just focus on the important things. Thank you.

「未来のオートフォーカス老眼鏡(Autofocusing reading glasses of the future)」の和訳