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Switchable bifocal contact lenses

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So, contact lenses.

My long-running argument with the world of opthalmic correction is that if, like me, you are both shortsighted and presbyopic, you are screwed. You need one prescription for near vision, and another set for far vision.

With eyeglasses, you can of course carry two pairs. You can also get bifocals or varifocals (which offer different prescriptions in different areas), and you can even get glasses whose focus can be adjusted.

With contact lenses, you can again get bi- or multi- focals, which (like the glasses) give regions of near and far focus. This, however, is not ideal.

The optimum solution for lens wearers would be contacts which can adjust their power (in the same way as some of the schnazzier glasses), but this is difficult to implement.

So, I was thinking of how you might do this. The first problem is that it's tricky to get power into a contact lens. You could use some sort of inductive coil embedded in the lens (and a transmitter carried on the person), but the power available in this way would be very, very limited. You might also have an annular region of solar cell embedded in the lens, but again this would give only a tiny power output. So, what can you do with such a small amount of power?

My suggestion is this.

The contact lens will consist of many (perhaps a few tens of) hexagonal facets. The facets are of two types, alternating across the surface of the lens. One set of facets are segments from a lens shaped for near-vision. The other set of facets are segments from a lens shaped for far vision.

Now comes the electronics. Each facet has an LCD pixel near its inner (corneal) surface. Thus, by choosing which set of pixels to darken, you can switch the lens between being a near-vision lens (with the far-vision pixels blanked out), or a far-vision lens (with the near-vision pixels blanked out).

What would this be like to look through? You would not notice the pixellation, because the pixels are way too close to the eye to be distinguishable. To the wearer, it would appear as if the contact lens were switching between a normal near-vision and a normal far-vision lens.

The only discernable effect would be that the brightness of the scene would always be reduced by 50% (since only half the pixels are "open" at any time). However, the eye adusts to light intensities varying by many thousands of fold, and a two-fold dimming will not even be noticed except in very dark settings.

Thus, you have a "switchable" contact lens with no moving parts, and which (since the power requirements of LCDs are very low, if they don't switch too often) can be powered by inductive coupling or inbuilt solar cells.

Control would need to be by a small transmitter, unless you could use inbuilt solar cells as a signalling device (eg, three blinks then one blink would be detected by the photovoltaic, and would trigger the lenses to flip between far and near vision).

MaxwellBuchanan, Dec 09 2011

Wikipedia explains chromataphores. http://en.wikipedia.../wiki/Chromatophore
[AusCan531, Dec 14 2011]

[link]






       Actually, the brightness would always be reduced by at least Ÿ, as LCDs block at least œ the light.
spidermother, Dec 09 2011
  

       Funny you should mention this. At this moment I am trying out the new laser-measured-prescription / laser-cut lenses.   

       They're great at distance and reading but the computer vision is a pain. I should have known better - I am never an early adaptor out of caution.
normzone, Dec 09 2011
  

       It would be good if the progressive switching could be initiated by detecting the subtle reshaping of the eyeball which happens when we try to focus on something. This would be better than your coded blinking idea but harder to design.
AusCan531, Dec 09 2011
  

       //The brightness would always be reduced by at least Ÿ// Yes, you're right. There'd also be issues with viewing LCD screens and other polarized light sources (I figured there'd be a way around that, like not having all the elements in the contact lens aligned the same way).   

       But, by the same token, if you look at the world through a polarizer, you don't notice any extra dimming of normal light (unless you're using glasses which are shaded, in addition to their polarization), which just goes to prove that brightness changes of a few-fold tend not to be perceptible.   

       //switching could be initiated by detecting the subtle reshaping of the eyeball // That's interesting. You might be able to put strain- guages into the lens to do that.   

       //At this moment I am trying out the new laser- measured-prescription / laser-cut lenses// I too have just received new lenses (one is bifocal, the other is not). They used the laser analysis (which is new to me), but then the regular eye test gave very different results.   

       Incidentally, I just realized that a hexagonal pattern of pixels is unnecessarily complex. Since the surface of the lens is so close to the eye, a fairly coarse pattern (perhaps even just a central circle for near vision, and a ring around it for far) would be OK. It's a bit like the iris on a camera: when you close the iris, you don't lose the edge of the picture, it just gets dimmer. (What I mean is, the pattern of alternate windows in the contact lens wouldn't appear as a pattern of windows on the image; so there's no need for a fine-grained pixel pattern on the lenses after all.)
MaxwellBuchanan, Dec 09 2011
  

       //It would be good if the progressive switching could be initiated by detecting the subtle reshaping of the eyeball which happens when we try to focus on something. This would be better than your coded blinking idea but harder to design.//   

       Anybody else sensing an application for piezoelectric generation?
ye_river_xiv, Dec 12 2011
  

       Since accommodation is normally accompanied by vergence, the switching could be initiated based on measuring the distance between the right and left contact lenses. If that's easier. Not sure it is.
mouseposture, Dec 13 2011
  

       //both shortsighted and presbyopic, you are screwed// - I am longsighted (hyperopic) and presbyopic and this too is a pain. Varifocals for hyperopia+presbyopia are worse than varifocals for myopia+presbyopia because in the 'reading' portion of the lens the presbyopia varifocals need to increase power (e.g. from +2.5 to +3.5) whereas with myopia+presbyopia the 'reading' bit of the lens reduces power (e.g. from -2.5 to -1.5). For me this 'high-power' bit of the lens performs quite badly. Anyway, as to the idea - another approach would be to make the lens out of an absorbent, but leaky sponge-like material. When it absorbs water from the surface of your eye, it would swell and become a more powerful lens. If your eyes are not producing much liquid then they would drain and become weaker lenses. Over time your body would adapt to the demands of these lenses, your eyes unconsciously watering when you wanted to focus on something close.
hippo, Dec 14 2011
  

       Hmm. I'm not sure that would work. The lenses will always be in contact with a roughly isotonic liquid film, regardless of how much surplus tear your eyes produce. Also, the response time would be a little slow.   

       I'm pretty sure it's well within our capabilities to produce a contact lens which uses micromechanics, microfluidics and electronics in some combination. In fact, compared to many other devices, such a lens would be rather simple.   

       The other travesty is that no useful research has gone into developing drugs to reverse the crosslinking in the crystallin which makes up the lens, and which is responsible for the loss of accommodation with age. It shouldn't be a difficult problem.   

       [Simpleton] the link is for a multifocal contact lens, which is the contact lens analogue of bifocal (or trifocal) glasses. (The difference from glasses is that, in a contact lens, the images from the different focal regions are superimposed on the retina; with trifocal glasses, you choose which area to look through.)   

       I'm wearing one at the moment (a multifocal contact lens, that is), and it's OK but far from ideal. I think its main problem is that, at any focal distance, an out-of-focus image is superimposed on the in-focus one. Thus, when I'm reading the black-on-white type on my screen now, I see pin-sharp letters but with a halo around each one.   

       The LCD idea would basically be a multifocal lens which would block out the out-of-focus parts of the compound image.
MaxwellBuchanan, Dec 14 2011
  

       Or, what about developing a gel-filled plastic lens which could be inserted into your eye to replace your current lens? This lens would be calibrated to the size of your eyeball (so, no hyperopia/myopia) and flexible enough to be deformed by your eye muscles (thus removing your presbyopia). I know they insert replacement lenses for cateract treatment, but I don't think these are deformable.
hippo, Dec 14 2011
  

       I was wondering about biologically-based lenses which utilize chromataphores rather than electronics or micromechanics. From my cursory reading and limited understanding of the linked Wikipedia article, I would suggest cephalopod chromataphores which activate "by muscular contraction, changing its translucency, reflectivity or opacity".   

       Better biochemists than I might be able harness this property to tie in to my previous notion about detecting changes in the shape of the eyeball when focussing. Heck, while these scientific geniuses have the cephalopod genome splayed over their lab bench they can employ the same genes which the cephalapods use to fashion their suckers to create a contact lens which NEVER shifts out of position.
AusCan531, Dec 14 2011
  

       I think a simpler option, if you're going the GM way, would be to modify the alpha-crystallin protein so that it's less crosslinkable and therefore doesn't lose its elasticity over time.
MaxwellBuchanan, Dec 14 2011
  

       I never suspected GM had this much techology at their disposal. I'm obligated to investigate for my own employer...
RayfordSteele, Dec 14 2011
  

       I think this LCD issue would work. But I suggest that you might be able to power it, and make it controllable if you use piezoelectrics. Piezo crystals produce energy when deformed. The eye deforms when focusing. The generated electricity may not be much, but as crystals, Piezo could also be clear. And as you say, the LCD only needs power when switching, and since the switching would only occur when your eyes naturally try to shift focus... I think it's a winning combo, albeit you may need a bit more power from some other source, such as the photovoltaic bits around the iris, as suggested.
ye_river_xiv, Dec 15 2011
  

       Would it not be simpler to make liquid filled lenses which deform by sqinting? The pressure of the wearers eyelids against the outer edges of the lens would cause it to bulge and change focus.   

       You know, [2fries], that is not such a stupid idea...
MaxwellBuchanan, Dec 15 2011
  

       As far as I'm aware (and I could be wrong...) some contact lenses are 'weighted' to keep them up the right way on the cornea (for astigmatism etc).
If a slightly larger lens was made 'bi-stable', and had two entirely separate areas for the near/far properties, a quick flick of the head would (hopefully...) tip the lens to its 'other' stable position, changing the view to the other part.
neutrinos_shadow, Dec 15 2011
  

       Hmm. I have enough issues with squinting and blinking as it is. If I start violently jerking my head, people will assume I'm deranged or Welsh or something.   

       But your anno does give me an idea: magnetically polarize the contacts so that they can be oriented by a discreet yet fashionable electromagnetic headband.
MaxwellBuchanan, Dec 15 2011
  
      
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