I can't see things very well at a distance. I used to wear classes, then contact lenses, then nothing. I hadn't worn any corrective lenses for years because glasses were annoying and my contact lenses were messing up my eyes. One day I was thinking about the reason for near-sightedness and I figured that if it's caused by an inability of the eye's lenses to flatten out, then maybe I could physically assist them in some way instead of just optically correcting for the problem like 'corrective lenses' do. Then after trying some things I realized that I could pull back back on the skin at the sides of my eyes and this seemed to do the trick. Since then I've been in several seminars in which I successfully used this trick to be able to read the screen or chalkboard that was too far away for me to otherwise make out clearly. So I decided to make a simple device to do this for me. What I made probably wouldn't be something that most people would want to wear in public, but a professionally made, miniaturized version of such a device might have more widespread appeal, and it was fun to make and test in any case.
Note: Squinting is thought to work by decreasing the amount of light entering the eye as well as by slightly flattening the eye's cornea. The cornea is a lens of the eye that is responsible for a majority of the eye's focusing power. If one squints one can notice a decrease in the field of vision indicating a decrease in eye's aperture. However, when pulling at the eyelid corners with your fingers you will notice an enhancement of distance vision greater than that achievable by squinting, and without any noticeable decrease in field of vision. So it seems that this system works more by flattening the cornea than it does by decreasing the eye's aperture. A final possibility for how this system works is related to the eye's length: In near sighted people light from distant objects converges slightly in front of the retina (the part of your eye that actually detects the incoming light and sends the information to your brain). Using this system the pulling back on the eyelids may be compressing the eye slightly, thereby allowing the convergence of light rays to occur further back in the eye: at the retina, allowing clearer vision of the distant objects.
Step 1: Get the linear actuator
you'll need a pretty strong linear actuator to be able to pull your skin enough to have the desired effect. I remembered that CD players had nice worm gear motors in them to move the laser back and forth across the CD, so I looked through my junk pile and found an old CD walkman. I tore it apart using screwdrivers etc. and took out the linear actuator assembly, this will look different depending on the CD player but it's easy to identify if you know what you're looking for. I didn't take photos of this part so you'll have to look at the photos I got from wikipedia (http://en.wikipedia.org/wiki/CD_Walkman, http://en.wikipedia.org/wiki/Compact_Disc_player).
= The first photo shows a portable CD player, you could also take apart a non-portable CD player but those are usually a little harder to take apart.
= The second photo show the inside of a CD player. The black region on the green board on the left is what you're after, it has all the necessary motors and gears attached.
= The third photo shows this same mechanism from the underside, showing the motors and gears. You do not need to disassemble this mechanism, you will use it as is. All you need to cut are the wires leading to the rectangular motor (as noted on the photo).
Looking at the third photo: We'll be interfacing with the rectangular motor which is connected to the worm gear which is connected to the laser lense. The laser lense gets moved linearly, up and down along the worm gear. A 'worm gear' is the best way to allow low torque motors (such as the small rectangular one in the photo) to be used in high torque applications (like this one), but some cheaper CD players won't use worm gears. These alternate gear configurations will also work ok for this application.
Step 2: Build the circuit
To control the motor I made the circuit shown below. The M is the CD walkman's motor. Cut the wires going to it so you can connect it to your circuit. The circles in the middle of the circuit diagram are transistors. You could also use opto-isolated photodiode arrays or other types of switches. Everywhere you see a '+' means connect that wire to the + side of your power supply (in my case 3 AA batteries). Wherever you see a sideways christmas tree that means connect that wire to the - side of your power supply.
This simple circuit uses a tripole switch (a switch with three settings) to control the linear actuator we got from the CD player. This switch is composed of my thumb, index finger, and ring finger, each of which has wires attached to them. By touching one's thumb to 1) the index finger 2) ring finger or 3) nothing, one can respectively turn the linear actuators motor counterclockwise, clockwise, or not at all.
This happens because in the first switch setting (thumbs wire touched to index finger wire) I'm connecting power (+5V) to the bases of two transistors (follow the blue line). These transistors, when actuated allow power to flow through the motor from left (the + power side) to right (the - power side).
Meanwhile, in the second switch setting (thumbs wire touched to ring wire), I'm connecting power (+5V) to the bases of two other transistors (follow the green line). These transistors, when actuated allow power to flow through the motor from right (the + power side) to left (the - power side).
Finally in the third switch setting I'm not touching my thumb to either the index or ring finger wire, so the motor doesn't get any power at all and therefore doesn't move. Because of the way that worm gears work, de-powering the motor will leave the laser lense at its current position, even if there is a force applied to it (i.e. if it's still pulling at the skin surrounding the eye). Again, this makes worm gear ideal for this application.
In the second photo you can see this circuit in its assembled state. I put notes in the photo so you can see what's what.
Step 3: Mount the system
Here's some photos of the control circuitry attached to my hand. The power supply is taped to the back of my hand. The wire contacts are taped to the ends of my thumb, index, and ring finger. The transistor array is danging by my wrist.
Also there's a photo of the head mounted part, i.e. the linear actuator motor. I tied a thing string to the laser lense and taped the other end of the string to the skin at the corner of my eye. To keep the string from slipping out from the tape I wrapped it once around (i.e. the string passes twice under the tape, and once over it). I was amazed at how well the electrical tape stayed attached to my skin, not once did it come off during use.
Step 4: Video and photos of testing
Here's photos and a video of the original tests of the whole system. I'm controlling the movement of the linear actuator by touching my thumb wire to either my ring or index finger (or neither). It worked pretty well and was able to pull the skin with enough force to cause the distance viewing effect I mentioned in the intro. Still, it took fiddling to get the mechanism positioned at the right height on my head to pull the skin at the right angle to cause the effect. Any future commercial version of this system would benefit from maybe three separate linear actuators, each positioned at a slightly different angle to allow one to customize the tensioning as required for their specific physiology.