But I don’t get it. Why would if I put a stronger lens, I wouldn’t be able to read the last line? She said you must have never been able to read the last line in your life, and she was correct, but I don’t understand the science at play here
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With current technology, lenses are made as a combination of a spherical component and a cylindrical component set at an angle. Your eye is not likely to have a distortion that exactly matches one of these combinations in its geometry, but some lens will give you some improvement. There is a best choice for a lens that improves your eye for a certain distance. There won’t be a “stronger” lens.
That isn’t to say future technology won’t be better. It might be possible to exactly tailor some surgery to make your eye perfect, but we are not there yet.
And most people don’t even know how good or bad their eyesight is. I remember taking a drawing class where the teacher liked my drawings but said they lacked sharpness. I had no idea what he was talking about until I got a new prescription. Until then, I thought my drawings were depicting the objects as they were, not just as I was seeing them.
You could have “glasses” that let you read that line, but those would be binoculars, not spectacles with a single lens per eye. Not a viable solution for day-to-day use.
Eyeglasses do not magnify what you are seeing (single lenses can be used to magnify, but magnifying glasses need to be held close to the thing being magnified), they fix the oddities in the shape of your eye. And once those are fixed, you may be able to get some tiny benefit from lighting, but likely the limiting factor in your ability to make out small detail is not your cornea or your lens, but your retina. In camera terms, and in a gross oversimplification, once you are perfectly focussed, it is the megapixels that matter, and your eye only has so many of those.
That line is likely small enough that hardly anyone can read it even with perfect glasses, that it is beyond the “megapixels” of the average eye. Nothing wrong with not being able to read a line, but if that got worse – if even with new glasses you could not read a line you could read before – that would be a sign that something is going wrong with your eyes and you may need additional tests and treatment. Your eyes should not lose a significant amount of “pixels” throughout most of your life.
I doubt it is the main factor at play here but there is an actual physical limit to the ability of a lense to resolve different points based on the diameter of the lens. No matter how perfect your eye is there is a fundamental physical limit to what detail you can discern.
Your overall vision depends on three aspects: (1) the sharpness of the image as it enters your eye, (2) the overall health of your retina itself, and (3) the sensitivity of your brain to interpret these signals.
Corrective lenses can help with 1 (that too not perfectly), but not 2 or 3. So people have a natural limit to how well they can see.
Glasses aren’t binoculars and don’t significantly enlarge what you see. They correct the lens of your eye so that it’s able to focus accurately, making the image you see as sharp as possible. If you still can’t read details then that’s not a focusing problem. Assuming you don’t have some other issue like cataracts, it means you’ve reached the detail limit of your retina, the part at the back of the eye that captures the focused images. Better glasses can’t help with that.
Yeah I used to be able to read the copyright19… made in line on the very bottom with each eye. Until about my mid 30’s I had better than 20/20 vision. I spend too much time on computers and it’s been notably downhill for a while now. Though I still see about average.
There are 2 physical limits to how small you can see:
One is the size of the light sensing cells in our retina. Once details projected on your retina are smaller than this there’s no way to see them.
The other is due to light physically not being able to focus on a perfect point but [a fuzzy disc](https://en.wikipedia.org/wiki/Airy_disk). Anything smaller than this will be blurred out by the light itself.
So even with perfect glasses and a perfect lens in your eye there are always limits to what you can see unless you magnify the image with a telescope/binoculars.
From the test distance a single lens over your eye is only going to adjust your ability to focus not substantially the size of the image on your retina.
So for a given base acuity (resolution) the average human would not be able to discern the last line. Which with normal or corrected vision is called 20:20.
That said there are humans who due to genetic differences have 20:10 vision or a little better. Which means they can see at 20 feet what the rest of us (even with glasses) can only see from 10 feet.
Having been an astronomer for quite a while I’ve found by observing & sketching the planets that for my right eye only & for a small sections lightly off-center I have an acuity of approx 30:10.
Take a 4k video and play it on an old tube TV. No matter how sharp you make the picture, you will never be able to make out the small details because the resolution just isn’t high enough.
Your eyes have an upper limit of resolution. The last line is has more detail than your retina could resolve even with a perfect focus.
It’s possible to have better than 20/20 vision, but that’s a “feature” of the eye, not something glasses can produce. The color-receptors (cones) on the retina are relatively large. There are lots of them in the focal spot of the lens, so while it’s the clearest picture it’s also a bit more “pixelated” than if the spot where just rods that react to light in general and can be more tightly packed.
Colorblindnesses can be due to a total lack of cones, and instead there are more rods in the focal spot. Tadaaah, better resolution, but worse color vision, and usually more sensitive to or easily blinded by light.
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