I want my scifi spectacles!

December 8, 2007 8:13 AM

What are the technical obstacles to making 'smart' spectacles which would function like the lenses in the human eye?

Like lots of middle aged people, I have Presbyopia and need bifocals (although actually I use two pairs of glasses).

Why can't I have a pair of glasses whose lenses are bags filled with fluid stretched into different lens-shapes by microcontrollers, so that they are truly varifocal?

Do such lenses actually exist on any scale outside the eye?

posted by unSane to science & nature (14 answers total)

Just a quick set of obstacles:
* The lenses in your eyes are manipulated by a set of many, many tiny muscles with incredible precision. I have no idea if we have anything comparable as a commodity, but the specs would be incredibly expensive because of these motors, and very difficult to maintain.
* Speaking of maintainability, you're going to notice EVERY TIME one of those motors breaks down. Ever get a dead pixel or a scratch on an LCD? Imagine how irritating an out-of-focus radial area of vision would be.
* The motors need power. It will need to be located on or near the head, or worn on the belt / carried in a pocket with a wire going up to the glasses. Would you be caught in public with one of those?
* More problems with style: Do you like clunky emo-kid glasses? These are sure to be large frames.
* Oh, and the motors will make noise, too.
* The lenses of your eyes are controlled subconsciously. These things are going to have to tap into your brain for a control source, and I'm sure we don't have a well-documented set of APIs for the control signals.
posted by tylermoody at 8:36 AM on December 8, 2007

Obstacle 1: How would the glasses know what you're looking at?
posted by weapons-grade pandemonium at 8:40 AM on December 8, 2007

One more: lens optics aren't that bad, but I have no idea about fluid optics. One of the nice things about solid lenses is that they're static. Every time you move your head, the inertia of the fluid in the lenses would deform the lens surfaces and screw up your vision.
posted by tylermoody at 8:41 AM on December 8, 2007

I want to believe.
posted by 517 at 8:57 AM on December 8, 2007

I got a few more while I was in the shower:

* The major variables in a lens that they teach you in freshman-year physics are the height (distance from the focal plane (the center of the lens) to the edge and the curvature of each side of the lens. These 3 variables are all essential to the magnification of the lens, which is the key feature for your glasses. Changing any one of them would alter the volume of the lens, meaning you'll need a fluid reserve in the glasses somewhere to keep the lenses at the proper pressure.
* If you look at your glasses, you'll notice that the distant side of each lens (from your eye) is convex, while the near side is concave. The curvature of each side isn't necessarily the same. Look at your glasses from the bottom: do they get thicker at the edges? Mine do. That's because one side is more sharply curved than the other. Fluid-filled sacs will tend towards spherical shapes when they're pressurized. Forcing such a sac into the correct shape would be difficult. Piston-style motors won't work; they might force a good general shape on the lens, but they'll leave dimples as the sac is deformed around their contact points by the pressure on the fluid.
* The fluid will be pulled to the bottom of the lens by gravity, distorting the lens shape. This could be relieved to some degree by putting the lens fluid at a higher pressure, but that means the motors need to exert more force to shape the lens (bigger battery, bigger motors, motors more likely to fail). The fluid-reserve system mentioned above will also be more likely to fail as the fluid pressure increases.
posted by tylermoody at 9:17 AM on December 8, 2007

A good bit of work is being done on biomedical adaptive optics, both lenses and mirrors. You might start here or here when looking at lens technologies. Research seems to be tending more towards replacing the lens in your eye, rather than constructing an external one. (Of course, external tunable lenses have existed for a while, but not 'glasses-sized'.) You might also be interested in David Williams's work at the University of Rochester, to use adaptive optics to build better contact lenses and eliminate the need for active glasses.

If you don't have institutional access to the first couple papers, send me a MefiMail and I'll email you copies.
posted by Upton O'Good at 9:38 AM on December 8, 2007 [1 favorite]

Obstacle 1: How would the glasses know what you're looking at?

This is possible, though I don't know if it can be miniaturized to the point where you'd want to wear it on your head all day.

One option would be to combine it with the sort of technology that goes into an autofocus camera. But that seems less ideal — how would it know whether you're trying to look at Mount Fuji in the distance or the fly right in front of your nose if the two happen to line up in your visual field? Better, I think, to use parallax to estimate the focal distance and go from there.

The lens design issues that tylermoody's raising seem like a bigger problem to me — but then, I don't know much about lenses. Maybe they're solvable too.
posted by nebulawindphone at 9:58 AM on December 8, 2007

I don't remember the details, but there was a company a couple of years ago that developed a variable-focus liquid lens for cell phone cameras. No motor (no moving mechanical parts at all), very low power, very tiny, very cheap. They got at least to the point of showing prototypes. Don't know if the technology has gone anywhere since.
posted by madmethods at 12:11 PM on December 8, 2007

Ah, I think the company I was thinking of is Varioptic.
posted by madmethods at 12:15 PM on December 8, 2007

Obstacle 1: How would the glasses know what you're looking at?

This is possible [as eyetracking experiments show], though I don't know if it can be miniaturized to the point where you'd want to wear it on your head all day.

Eyetrackers would tell you in which direction you're looking, but it wouldn't tell you how far away the object you're looking at is. That's the real issue here. You'd definitely need to combine eyetracking technology with autofocus camera technology.

Autofocus mechanisms in cameras get this information in one of two ways. Active autofocus cameras toss out an infrared ray or use sonar or something like that in order to gauge distance. Our hypothetical varifocal glasses would probably need something like that, which seems fraught with problems (although I guess it might be possible). Passive autofocus cameras move the lens back and forth, all the while performing computations on the incoming image, until it gets to what it considers the nicest-looking image (I gather that something like this goes on in the brain and manipulates our ciliary muscles, though I don't know for sure). The problem with this is that the hypothetical glasses, imagined as sacs of liquid, don't take in any light array as input. You'd need a camera on the bridge or somewhere that could grab light information and perform computations on it.
posted by painquale at 4:06 PM on December 8, 2007

Eyetrackers would tell you in which direction you're looking, but it wouldn't tell you how far away the object you're looking at is. That's the real issue here.

Well, an eyetracker alone won't tell you how far away the object is.

But if you track both eyes, you can compare the angles and calculate the distance to the object that way. The farther away the object is, the closer both eyes will be to looking in the same direction; the closer it is, the more they'll be crossed.
posted by nebulawindphone at 6:45 PM on December 8, 2007

OK, that's true. Silly me.
posted by painquale at 8:14 PM on December 8, 2007

I think the simple answer would be that
1. Yes, they could be made, and could probably work quite well.
2. They will not be made (in the near future) because there would be no market for them, due to factors like their expected high cost/bulk/weight/fragility/inconvenience ensuring they are a highly undesirable purchase.

It could make a pretty cool DIY project though. And I expect the march of technology will eventually make such a device more market-friendly.
posted by -harlequin- at 9:26 PM on December 8, 2007

Never mind everything else, these would be heavy. I don't know about you, but I love how light my spectacles are, they don't slide down my nose, and apart from the sharp vision, I hardly notice I'm wearing them.

Bags of fluid is bad thinking. Some sort of deformable polymer would be more manageable. A material that flexes when some known current is applied would be easier to manage than something that required pumps or servos (materials like this exist, but I don't think any of them are transparent, so it might be the frame that would do the distorting, flexing the lens). This would have the benefit, according to your criteria, of operating more like our own eyes than any bags of fluid.

Others have rightly pointed out the difficulty of knowing when to do this. Automation would seem impractical (unless you're prepared to wear some ludicrously over-sized contraption on your head). So perhaps you could have an external controller, a small pocket device which allows you to push a button (or a slider if you want to be able to vary the effect along a continuum).

I'm totally with you on wanting more science fiction in my life, but at the moment this still seems rather impractical. Now, if they could look like normal stylish glasses, and provide a HUD, I'd totally be in to it. (I mean, not that I need multi-focals, I just want a HUD in my 'normal' specs.)
posted by The Monkey at 3:25 AM on December 10, 2007