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]

[0] https://en.wikipedia.org/wiki/Vergence

[1] https://en.wikipedia.org/wiki/Accommodation_reflex

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.

[2] https://en.wikipedia.org/wiki/Prism_correction

[3] https://en.wikipedia.org/wiki/Dioptre

[4] http://www.langleyflyingschool.com/Pages/Human%20Factor--Emp...

Edits: clarity; 100x, not 1/100x

Addendum:

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