I recently underwent an eye exam with pupil dilation. I am nearsighted with a -3 prescription or so. When the dilation sets in, it becomes hard to see up close, so if I want to read something (like my phone), I actually have to hold it further away, maybe 3 feet from my eyes. I assume this has something to do with the medication preventing your focusing muscles from engaging in close focus. The doctor mentioned that this is kind of what presbyopia will be like when/if it sets in.
Anyway, I noticed that my vision for reading my phone 3 feet away was significantly worse with my glasses on. I couldn’t read the phone with my glasses, but if I removed them I could read them (with some difficulty). The short-medium range vision definitely improved with my glasses off. Is that normal? What was the reason that happened?
Normally, the opposite is true. If you reduce the aperture that you’re looking through, then your vision improves, because the aberrations are smaller and your effective depth of focus is much larger. This is why pinhole glasses work. You see much better, but at the cost of reducing the amount of light entering the system. Everything is dimmer. (But if you have plenty of light, it’s a good quick and dirty substitute for glasses. One outdoor magazine article suggested makeshift pinhole glasses for hikers with poor eyesight who lose or break their glasses. Burgess Meredith could’ve used this trick in the Twilight Zone episode where his character, with “all the time in the world” to read – breaks his glasses. I’ve suggested that this trick might have been used in classical antiquity, but archaeologists missed it because they didn’t know what to look for.)
But with pupils dilated your aperture is bigger, and any aberrations that depend on aperture will be even worse. Your depth of focus will be smaller. I’;m not sure why your vision in the medium range was better with dilated pupils alone than with dilated pupils + glasses.
I’ve noticed a similar effect when my pupils are dilated - I lose my up-close vision while using my glasses, and also that my depth of field is smaller. I suspect that the drops used to dilated one’s eyes also affects the focusing muscles, mostly not allowing you to focus in closely so your eyes are set at “distance viewing” for the duration.
I do think your focusing muscles are affected, which is why your close vision is poor, but I don’t understand why having the glasses on makes your close vision worse, since under normal circumstances the way they bend light does not impact your close vision (it’s the same whether you’re wearing glasses or not if you’re nearsighted).
This is kind of answering your own question, I think. Age-related presbyopia doesn’t just change your focusing abilities such that you can no longer focus effectively close up, it also (in many cases at least) causes improved farsightedness.
I used to be mildly nearsighted, just enough that I’d only wear glasses when driving. Then about 6 or so years ago I was getting headaches wearing the glasses and everything was blurry. I thought I needed a stronger lens prescription. Then I took my glasses off to rub my eyes while stopped at an intersection, and everything was clear! An eye exam confirmed I had close to 20/20 vision, and I’ve never needed glasses when driving since. About the only thing abut myself that’s improved with age (including wisdom). the tradeoff is, I need cheaters to read just about anything.
Even without the drops my glasses “impair” my near vision compared to going bare. Without glasses the further I can see clearly is about 4 inches, but without it’s like wearing magnifiers. Which is why I take them off to thread needles or look at very, very fine details I can’t focus on while wearing my glasses.
With eye dilation this effect is only increased. I’m left with just the middle vision I have with glasses. Without the glasses I can’t see quite as up close as usual and, again, I’m left with “middle vision” which is… 2-3 inches? Not very useful.
Myopia, near sighted, means the distance from the lens to the retina is too big .
The lens is relaxed for long distance vision , but because it can’t relax negative amounts, the longest distance the myopic person can see is short… They can focus their lens, but this means they can see their fingerprints very well, like, with their finger at 2cm from their eye… they can focus on things right up in their face… the ability to change focus is called “accommodation”… So with correction, they can focus on the infinitely long, and they can focus on something close, as close as their accommodation allows… such as , 50cm away to a book or computer screen…back to normal “range” (infinity to 50cm,…) oh the myopic range, guessing , from experience… could be 10 metres to 2cm ? You could look up a table of the range pairs , nearest,furtherst, as the myopia increases… .)
With the presbyopia eye, the accommodation is reduced, so the closest they can focus is moving further away … the lens isn’t adjusting the same amount any more… so its still able to see long distance when the focusing muscles are relaxed… So they can focus on distances from infinity into 1 metre, for example … so they hold the book at arms length to try to read it, as the book is now at about 1 metre , instead of 50cm… but the correction causes them to be short sighted WHEN CORRECTED… they can’t relax their lens to get back to infinite focus…