There's been a practical solution to this problem for years - standard round lenses. Spectacles have three parameters - spherical radius, cylindrical radius, and axis. For round lenses, axis is set by mounting in the frame. There's a notching tool which notches the lens so it's retained in the frame at a fixed angle. So you only need a set of a few hundred standard plastic lenses, which fits in a small suitcase.
This was developed in India decades ago, but I can't find those kits online. Obsolete?
I got so frustrated with eye glasses that never had the correct prescription that I purchased an optometrist kit off Amazon for $200
I had spent over 10,000 at various eye doctors.
Helped me figure out what was going on. ( unstable prescription)
Same for me, except my prescription is stable. The first doctor I went to got it wrong, and every doctor since was too hesitant to change it. One even got it right, but said nothing had changed... They missed that the axis was significantly different, and that had been the problem all along.
I've actually been thinking: Since glasses can theoretically make objects a certain distance away appear arbitrarily far away to your eyes/brain, could a pair that makes your desk/screen appear infinitely* far away prevent any harmful effects of constantly focussing nearby? That is, if there any--AFAIK, there's no conclusive research regarding nearsightedness or 'eye strain' (which I haven't even seen a satisfying definition of). In any case, focusing far seems more natural,* and I also wonder if a computer screen that appears large and faraway would acquire some of the effect of a TV/theatre.
Correct me if I've erred in the theory below; eyeglasses can be had online for so little that I'm considering ordering a pair if only to see what how it feels.
Typical glasses/contacts prescriptions aren't enough: To a single eye, a corrective lens is indistinguishable to moving everything in the world closer or farther away, but our binocular vision isn't fooled.[0] Your brain would still think the screen is nearby, only you'd have a hard time focussing on it because of the unexpected power required.[1]
But the required trickery is exactly what's prescribed as prism correction[2]--a displacement of the world as seen by each eye by a specified angle. The unit of measure, prism dioptres, is conveniently defined as 100 times the apparent distance that an object at a certain distance is displaced by. In our case, we want to, for each eye, displace the screen (which is a known distance away) by half the distance between the eyes, so that the eye must look straight ahead to see any point on the screen, as it would if the screen were infinitely far away.
i.e., a prism power of:
100 * 0.5 * (pupillary distance) / (distance to screen)
Optical power can also be calculated: The power of a lens, measured in dioptres, is the inverse of its focal length (in metres).[3] If you're nearsighted, 1 divided by your prescription is thus exactly the farthest distance you can focus without glasses! Light coming from a point on the screen diverges, but light coming from a point infinitely faraway is parallel; in order to make the light from the screen parallel, the lenses need a focal length equal to the distance to the screen.
Optical power is approximately additive, so including existing correction:
1 / (distance to screen) + (power of prescription)
*I've always read that the eyes at rest focus at infinity, but recently learned (via HN) about empty-field myopia[4], where the eyes of a pilot staring at empty sky naturally focus only a couple metres away. So which is it? Closing my eyes for a few seconds confirms that they definitely don't remain focussed up close, but the accommodation is so fast when I open them that I can't really tell where they've settled.
The prisms are horizontal and base-in. To actually make something 500 mm from your eyes appear infinitely far away, given a typical pupillary distance of around 30 mm, would require a very high prism power of 6. The typical max seems around 5, though, which isn't too far off.
Illustration: Rays of light (/\) originating from a point (.) pass through the glasses (=<|==|>=), become parallel as if originating from infinity (|| ||), pass through the cornea/lens of each eye (<=> <=>), travel through the eyes (O O), and converge (\/ \/) on the retinas into images (* *).
.
/ \
// \\
// \\
/// \\\
/ / \ \
// / \ \\
/ / \ \
_,,,-^^^| |^^^-,,,_
==<________|=========|________>==
| | | |
|___| |___|
O<_____>O O<_____>O
O \ / O O \ / O
O \ / O O \ / O
O * O O * O
I wonder if an easier solution, albeit maybe a bit too cyberpunk dystopian, would be to just work in a pitch black room where you could use a projector shining on the farthest wall.
You'd have to be able to touch type though, otherwise every extra inch of distance between keyboard and monitor is somewhat fatiguing when you are constantly glancing up and down.
Tried it. Big 4K screen across the room. Spent a year in a pitch black room with one eye covered. Sorta worked, but not well. Diamox fixed vision issue much better.
"a corrective lens is indistinguishable to moving everything in the world closer or farther away"
This is not how it works. You seem to confuse focus and magnification. That said the display in VR goggles is set at a specific focus distance, and there is a fair chance it is set at infinity. When you look in VR goggles you eyes are at rest, focus-wise. Seems to be what you are looking for.
Oops, I oversimplified that explanation. Add, "...and scaling it to have the same angular size". The image on each retina is indeed around the same size as before, only the object is now perceived as massive and distant by the brain.
The simple formulae I used only approximate the glasses and eyes as stacked thin lenses, so there'll be a bit of magnification in practice. I think this is the norm in optometry, though--apparently, the brain adapts with no issue to the mismatched peripheral vision when wearing glasses.
Hmm... Actually, I'm not sure whether practical optometry involves any calculation at all: As I understand it, the optometrist has you subjectively compare lenses that are positioned in the phoropter at the same distance to your eyes as those in your spectacles would be. So the required lens power is measured directly, without any maths.
Strangely, info on how a phoropter is used seems to be entirely missing from the web (i.e., search engines). There really isn't any pop-sci interest?
Yes. Huds for example usually are made so that the image seems as if it's floating in the distance.
Ultimately one could have a light field display to achieve all this in a flat package. It would be like a display consisting of small directional mini displays. It would have some resolution and brightness issues and would be expensive.
This is enough for the basics, but modern lenses are more complex. Eg multifocals for basically anyone over 45, or high end custom lenses that can correct higher order aberrations.
Anyway, the optometrist lenses kits are still there, you can order them from aliexpress.
This was developed in India decades ago, but I can't find those kits online. Obsolete?
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