h a l f b a k e r y
Yeah, I wish it made more sense too.
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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
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.
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-
which (like the glasses) give regions of near and far
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
the schnazzier glasses), but this is difficult to
So, I was thinking of how you might do this. The first
problem is that it's tricky to get power into a contact
You could use some sort of inductive coil embedded in
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
out), or a far-vision lens (with the near-vision pixels
What would this be like to look through? You would not
notice the pixellation, because the pixels are way too
to the eye to be distinguishable. To the wearer, it
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
the scene would always be reduced by 50% (since only
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
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).
Wikipedia explains chromataphores.
[AusCan531, Dec 14 2011]
||Actually, the brightness would always be reduced by at least Ÿ, as LCDs block at least œ the light.
||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.
||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.
||//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.)
||//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?
||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.
||//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.
||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
||[Simpleton] the link is for a multifocal contact
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
I'm wearing one at the moment (a
multifocal contact lens, that is), and it's OK but
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
||The LCD idea would basically be a multifocal lens
which would block out the out-of-focus parts of
the compound image.
||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.
||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
||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.
||I never suspected GM had this much techology at their disposal. I'm obligated to investigate for my own employer...
||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.
||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...
||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.
||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
||But your anno does give me an idea: magnetically
polarize the contacts so that they can be oriented
by a discreet yet fashionable electromagnetic