A plus correction for distance ? How can it be?

How can it be that someone has a prescription of + 3.0 for distance? He has also presbyopia and for that has he needs a correction of +5

What happened here? His eyeball actually got shorter than the emmetropic and the picture falls behind the retina now ? I don’t get it :face_with_monocle:

it is like one of the members here without doing anything, goes from -3 to perfect distance vision.

Could it just be that they are far-sighted, and so need plus lenses for that. The qualifier “for distance” is to distinguish that from additional +2 he now needs for close work due to the presbyopia.

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At some point of refraction distance and close-up isn’t a thing. For example with like -3 refraction you need minus lens to see even a book, though minus is to see distance. It’s the same with hyperopia. Your close-up problem is at the horizon so you can see only blur without any plus lenses.

Pretty normal hyperopic presbyopic prescription. He’s just not myopic.

his wife if presbyopic too but doesn’t have this problem for distance. so it brings me back to my question - how can it be and what is the physical explanation of that?

Another question is what should he be using for differentials?
How do we calculate that?

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Eyeballs too short instead of too long.

We are all born farsighted, and most of us drift myopic over time. Ideally we stop at 20/20 vision. Being farsighted is rarer than nearsighted, but without near work and lenses it would be just as likely. Near work and minus lenses drive myopia progression further than it would have gone otherwise.

Personally, I’m myopic genetically as well as by habit. My father and grandfather both wore glasses before it became so common. Those genetics make me more susceptible than most. My doc says I’m tied for most myopic patient in his practice.

If you’re born susceptible to hyperopia, you never reach 20/20 in childhood when you should, you get fitted for plus lenses, and lens induced hyperopia progression can set in. The same mechanism EM is using to improve myopia causes hyperopia in those that see 20/20. The case you quote seems mild though.

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The math for differentials is the same if you keep your positive and negative numbers straight, it takes more plus or less minus to do near work.

There only difference is that you are going more minus when moving both those numbers towards 0.

that is my only guess as well but if that was true then going beyond 20/20 won’t produce a better eyesight but worse. for example , 20/15 wouldn’t be regarded as better vision but worse.

another thing, if this is true then what is this ocular condition is called?

well I have the answer!! :innocent:

at first it was not clear to me because all the sources I was reading about hyperopia specifically were stating a problem looking up close but no problem in the distance (even stated clear vision).

let’s say I didn’t expect to find the answer in wikipedia… :flushed: :
" Far-sightedness , also known as hypermetropia , is a condition of the eye in which light is focused behind, instead of on, the retina.[2] This results in close objects appearing blurry, while far objects may appear normal.[2] As the condition worsens, objects at all distances may be blurry".

:man_facepalming:

it means that if someone keeps trying to improve his eyesight beyond 20/20 or 20/15 then he might develop again problem with seeing clearly in the distance, this time from the other side of the myopia (meaning, the hyperopia), if I understand it correctly. :bowing_man:

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This is what I said 14h ago in this topic.

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I read your reply before and now again and still don’t understand how it is similar to what I have just found. maybe I didn’t understand your answer correctly… :thinking:

this person started to have this problem only at age 50…

I was going to say no - once you can see to infinity, you can no longer get a blur horizon in order to use AF to go any further. But I think I’m probably wrong - if you were to use plus lenses, you probably could carry on and keep shortening the eyeball.

But there’d be very little benefit because you wouldn’t improve your distance vision. Once your focusing system can see to infinity the limit (based on https://wiki.endmyopia.org/wiki/Distance_vision) is resolution of the retina. Carrying on would let you see “beyond infinity”, ie you could focus even converging light. (Don’t worry, it’s just the way physicists think about things…) But that would come at a cost of incurring far-sightedness, pushing out your near point and limiting close vision.

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I am not so sure this is right.

If someone needs +3D to see 20/20, (lets assume no presbiopia)
And wants differentials for 50cm,
Then are you are suggesting he use +3 +2 = +5D ?
Won’t this prescription make things worse?

The stimulus that he needs to improve his vision is not distance vision, its near work (he needs to lengthen the eye)

So doesn’t he need +3 - 2 = +1D to work at 50cm, and gradually get the screen closer?

This is actually something I had been meaning to ask about… my understanding of far-sightedness was that the eyeball is too short (for the focusing system), and so the near point is pushed out. But as long as it’s not pushed out as far as 20 feet, wouldn’t they be able to see fine at 20ft ? They would have to accommodate more than a “regular” person to do so, but that should still be okay, shouldn’t it ? (I’m using the term accommodate to mean activate ciliary muscle to increase focusing power, rather than possibly the more general term of just adjusting the focus.)

I’ve not thought much about far-sightedness, so have probably got all this wrong… this is just me thinking out loud, and possibly making a fool of myself.

Is the purpose of differentials to be able to view (eg) screen in a relaxed state. In my odd view of the world, glasses move the real world forwards or backwards to map it into the range your eye can focus at. For a myope, differentials map screen-distance to blur-distance, whereas full prescription would map it much closer (since it has to map infinity to the blur point, and therefore fit all of the rest of the world into the limited space between there and your eye).

For a hyperope, the full prescription “pushes the world away” a little, so that things that are close in the real world are mapped to your near-point blur horizon. But that doesn’t push your computer screen very far away. in order to put the screen at the fully-relaxed point, you’d want to push it away much further than usual (to infinity and beyond, as it were…) So yes, I guess that would require a stronger than usual correction. Things closer than your near point would become visible. I guess things beyond the screen would become blurred. (Err… myopic blur, I guess, since they’d be focused in front of the retina …?)

In order to use differentials to actually exercise your AF when your far-sighted… that might be a bad idea. Dunno. Does Jake say anything about farsightedness in the endmyopia program ?

The problem is that to induce an eye-lengthening stimulus, you’d presumably need to look at something such that it is focused slightly behind the retina. But the eye’s going to be fighting you by activating the ciliary to try to resolve the blur. So you’re going to have to be at full accommodation in order to provide this stimulus. (Have I got that the right way round…?) If you set up your glasses and your screen to try to provide this stimulus for hours at a time, you’re presumably going to get ciliary lock-up. Which I think would be a bad thing.

Myopia, has the convenient property that AF happens at the point where your eyes are relaxed anyway. (For a suitable definition of relaxed.) So if you’re wearing your differentials and lean back from your screen slightly, you get a blur and you can practise your AF. (Note, this isn’t from personal experience - I’ve not yet got to grips with AF.)

Does an analogue of the endmyopia program even work for far-sightedness ? I’m trying to think what would be the equivalent of lens-induced progression. What could you be doing to cause myopic defocus that would stimulate the further shortening of the eye ? ISTR far-sightedness is usually just because your eye didn’t lengthen enough during early development.

Not exactly. There’s more to vision than just refraction. To have eyesight better than 20/20 you have to have better than average processing of the light that hits the back of the eye. I don’t buy any of the claims of “over-correction” due to reading too low on the 20 foot Snellen chart with glasses. Over correction causes blur at close distances. Having too much minus lens in front of your eye makes the font smaller, so it doesn’t do any good on acuity tests to go past maximum clarity.

Hyperopia. The opposite of Myopia.

May have been mild enough to not need glasses until presbyopia set in, then wearing reading glasses for distance work caused progression just as distance glasses for near work does.

No, you’ve got your signs backwards.

Someone with -3D adds 1.5D and gets -1.5D
Someone with +3D adds 1.5D and gets +4.5D.

All the myopia numbers are for minus lenses, you loose that minus and that’s when it gets confusing. You keep your signs straight and the math is the same. More plus/less minus for near vision.

AF for hyperopes would be the opposite, looking at near objects when under corrected for near vision. A hyperope needs the same stimulus that made the myope.

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I must say that preior to writing this post, in every source I have looked, hyperopia was a condition that affects only close up, so this is why I was led to believe hyperopia can’t affect distance vision at all and I was looking for the right condition that affects also the distance vision, until I have found it in wikipedia and another source :roll_eyes:

an incomplete (and thus misleading) sources:

generally on the internet the common definition of hyperopia is a condition that makes nearby objects look blurry and this is not accurate to say at all and it was even difficult to find the right definition and luckily it was all this time right under my nose, on wikipedia… :flushed: