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.
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,
接近 6.5 公分的对焦能力，
if you wished to.
By your mid-20s, you have about half of that focusing power left.
10 centimeters or so,
剩下大概 10 公分，
but close enough that you never notice the difference.
By your late 40s though,
the closest you can focus is about 25 centimeters,
你最多只能对焦大概 25 公分，
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,
当你 60 岁时，
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.
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?
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
我们找来了大约 100 名老花患者， 让他们测试我们的装置，
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 --
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.