Put the knife down and take a green herb, dude. (c) Ruffin Bailey 2001-2021

I’ve been meaning to find time to write this up really well, but haven’t, so let’s not let the perfect get in the way of the wholly inadequate. I have not finished writing, much less editing, this one. Not that you’ll be able to tell comparing to my other posts. ;^)

Nearsightedness and presbyopia:

Presbyopia stinks. You get old, you stop being able to focus on things that are close to you. You need reading glasses to read. Or, if you’re already nearsighted, you need to get “multifocial” lens, meaning, at its simpliest, you need two different corrections:

a lens to correct nearsightedness to allow you to see far away, and
a lens to correct the correction, because your “far” vision now goes TOO FAR!!1!!, that allows you to see near again, but farther than the 6-8” your nearsightedness allows.

If you’re nearsighted and wear contacts, you see this just like any normal sighted person. You can see far away with the contacts but, slowly, reading things becomes blurry. You get readers to put over your contacts and the problem is solved. Sorta.

If you are nearsighted and wear glasses, one key symptom that tells you you’re descending into presbyopia (well, for me) is that you start moving things under your glasses’ lens. That’s because your nearsightedness still works. Your presbyopia isn’t bad, and there’s really only a very small range of tiny stuff that’s blurry, and you can probably get around this by simply bypassing your glasses. Maybe if your nearsightedness isn’t too bad you can get away with reading with your glasses off.

These are signs! Multifocals are near!

Types of multifocal lens:

Let’s cover the types (and I need to add a few more here later) of multifocal lenses.

Keep in mind all of these multifocal lens types exist because of nearsighted people with presbyopia. One lens is enough to fix your nearsightedness when you’re young. Then you get prebyopia on top of it and we need to correct twice. Then your presbyopia gets so bad you can’t focus on books and computer monitors with the same lens, and you need three — distance, reading, and monitor/intermediate length fixes.

But you can always take your glasses off and see six inches in front of your nose again. Well, most of us.

image from Quora

progressive lens images (with added label) from Zenni Optical

Bifocals:
- You have one prescription for far vision and another for close/reading vision.
- I like bifocals b/c there’s one clear line of demarcation where things change and zero lens-induced blurriness, unlike progressives.
- Types:
  - D-shaped or moon shaped
    - This seems to be common now.
    - The advantage for me is that side peripheral vision is all distant, making walking easier.
    - The advantage for people making the lenses is that they just stick ("ADD") a lens on top of the conventional one to change the prescription. Simple.
  - Executive/straight/Franklin:
    - One line cuts all the way across the lens.
    - The original bifocal.
    - Actually pretty rare now, afaict.
    - Takes a true optician, I think. You don't just paste a lens on top. You're putting to lenses together.
  - Golfer bifocal
    - Glasses mess up my peripheral vision badly enough I can’t golf with them at all, but...
    - Some people have the same issue with bifocals messing up their swing as the change in vision between lenses is jarring.
    - These fix that by giving all distance vision except a small bifocal in the outside bottom of your dominant hand side's lens.
    - Now you can see your scorecard in that window (and only through one lens), but your peripheral vision towards the hole is completely clear.
Progressives
- These are the slick lenses that cost a lot more and don’t have any lines.
- You look young again! (Ha ha ha. No you don't. Sorry. But your glasses do!)
- Everything you ever wanted to know about how they work
- Here’s the key: Progressives expect you to move your head in the direction of what you want to view, not your eyes. They completely discount peripheral vision.
- Types:
  - Normal three-distance lens
    - Note that the “distance” portion in the pictures above and below is pretty phat.
    - Intermediate or PC distance is super tiny
    - The close up/reading is better, but note all the area without a label. That’s where the progressive trick leaves useless glass. You can’t see out of this part of the lens
    - Advantage over bifocals: You can ostensibly see your computer montior with the third range, intermediate.
    - Advantage over trifocals: There are no lines, so you look OH SO YOUNG.
  - Near-range progressives
    - Sort of two distances, close (reading) and intermediate (computer monitor)
    - Emphasis on the reading.
    - Advantage over bifocals? Reading area is larger than your typical D-shape overlay.
    - DON’T DRIVE WITH THESE
  - “Office" or “computer” progressives
    - Same as near-range, with two distances supported.
    - Emphasis is on intermediate distance. PCs.
    - Advantage over bifocals? You don’t have to tilt your head to see your computer monitor.
      - Trick question: If I had bifocals with intermediate vision in the “main”/top lens, aren’t I doing just as well?
      - Better yet, if I had bifocals with a higher segment line, distance on top, PC distance for the bottom (but now over half of my field), aren’t I doing better?
    - DON’T DRIVE WITH THESE EITHER. THERE’S NO DISTANCE LENS.

Progressives stink for computer work. No, seriously. Check out the “blurry area” and the area for “PC” in normal progressives. This is useless.

image from Michael Penczek at youtube

Here’s a decent but long explanation of why the lens has blurry spots — the “optical swamp” as this guy puts its. I’ve got it cued to showing a trifocal equivalent of a standard progressive where he’s showing how close the three lenses are in the middle of the compound lens, which gives you an idea of where the “sight corridor” (the part down the middle where you can see in a progressive) comes from.

How bad are progressives and their crappy “optical swamps”? Bad enough that Nikon has a range of lens that run over $450 to get just the tiniest improvement to that vision corridor.

Um… wow?

You know what doesn’t have the swamp? Bifocals and trifocals. Bifocals and trifocals don’t have a swap, and can have 100% coverage for intermediate vision.

Nearsighted Superpowers:

But here’s the deal: You don’t necessarily have to get multifocals when this starts. Because it’s not that you can’t see close any more. It’s that your eye doesn’t allow you to focus on as large a range of corrective distances any more.

And here also is your nearsighted superpower: Before presbyopia set in, you could see things that were INSANELY CLOSE!!!

I remember getting a hair cut and having a small hair fall into my (skip to the next paragraph if you’re squeamish) tear duct in my eye. When I went to the eye doctor to be sure, he thought I was just guessing when I said that was what happened. But I really could see it in the mirror when I got up close. He needed some serious magnification before he said, “Hey, you’re right!”

If you’re nearsighted and probiscus-endowed enough, you might be able to focus on the end of your nose with this super power. Or do watchwork without a magnifiying lens. It is a superpower.

But though your range comes in lots closer than an average human’s, it also stops well short of theirs too. So you get glasses, give up your superpower (at least while your glasses are on. Who does this sound like?) and go on your merry way.

As you get presbyopia, you lose a little of this superpower. Your range decreases. You can still see clearly 6-8" (or whatever for you) away from your face, but not the end of your nose any more. Still superpowered, don't get me wrong, but the range has diminished.

The $7 trick to put off multifocals:

With what comes next, please recall that I’m not a doctor, just a middle-aged myopic. Please consult your eye specialists for what’s right for you.

And therein is the trick: Your optometrist or opthalmologist corrects based on getting things perfect at 20/20 or beyond. They want crystal clear distance vision.

They moved your vision's range from SUPERPOWER CLOSE to eight inches to a normal range of about five inches to INFINITY AND BEYOND.

What if, and stick with me here, i wanted to trade crystal clear mountains in the distance for skipping the multifocals? What if I ordered slightly less powerful single focal lenses that allowed me to see my computer monitor perfectly at the expense of seeing the clouds in HD?

That is, what if I wanted my corrected range to move from (5" to INFINITY) to (18" to REASONABLY FAR AWAY SO I CAN STILL DRIVE)?

Again, presbyopia does not mean that a nearsighted person can’t see close up. Of course you can! Not quite as super-power style close as you once could, but still much closer than the general public.

Presbyopic myopics have lost some range in what they can see with single focal corrective lens. You can’t focus as close, which means the range you can focus on with your single focal glasses is constrained. You could probably see to the ends of the earth with good glasses when you were young. Now you might have to trade that for seeing a half-mile out with extreme precision so that you can focus on a computer monitor easily.

And that’s exactly what the bottom half of bifocals do. The give you a weaker prescription by whatever your ADD value is. You take your negative value for your prescription, -4 or -5.75 or whatever, and you add a value to it — though note that that’s not where ADD comes from. Your bifocal lens is simply a less powerful prescription for nearsightedness.

If you had your bifocal bottom lens' prescription in a single focal lens, you could see a lot more of whatever’s close in your visual field in focus clearly. But far away would be a pain. But because you probably don’t need super-close vision, you can get what I’ve seen advertised as “computer glasses” that focus on somewhere between reading (bifocal bottom half) and distance (bifocal top) to bring intermediate sight perfectly into focus.

Note that I'm not talking about are not “office progressives” — those are multifocal lens like those on the right side of the Zenni image showing three progressive options, above. These “computer glasses” are single focal lenses that are less powerful than your distance prescription by about half your ADD. Zenni Optical describes these sorts of glasses here.

When you’re just getting presbyopia, the concession between your full distance prescription and half your ADD is very small. Back up .25 or .50 on your nearsighted prescription (from 5.00 diopters to 4.50, for example) and see how that works for you. You can probably wear them all the time (like I did for a few years — remembering that you might want full correctives or multi-focals for driving) when you’re just starting to lose your range of sight.

A place to try this out for cheap:

I’ve gotten glasses on the cheap from Zenni Opitcal for years. Zenni has a frame I really like — doesn’t look horrendous, is pretty resilient (some of their plastic frames are crap) — that’s $6.95 with lenses. No kidding. With $5 flat shipping per order, there’s really no reason not to play around a little. And since I took the “computer glasses” idea from their website, so they’re game to play with your prescription a bit. I've ordered several prescriptions at once in different frames so I could try a range of different intermediate distance values.

So give the “computer glasses,” but maybe with personally tuned partial ADD values, cheat a try. Even though I’m slowly getting past the point that I can use a single precscription for everything I need to see, it postponed getting multifocals for a few years. I also still use them when I’m on the computer, allowing me to see everything up to about two feet clearly, which is perfect for getting work done.

It sure beats the heck out of tilting my head up (bifocals -- though admittedly now I'd like to custom order lenses that simply move the line up on bifocals and have distance vision start just over the top of my monitor) or moving that small dot for intermediate vision directly at the spot I want to view (progressives). And when they were good enough for driving too, well, it wasn't bad at all.

Labels: Other Stuff, presbyopia

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Saturday, November 21, 2020
Don't get progressives just yet: How presbyopia works for the nearsighted and a $7 alternative I’ve been meaning to find time to write this up really well, but haven’t, so let’s not let the perfect get in the way of the wholly inadequate. I have not finished writing, much less editing, this one. Not that you’ll be able to tell comparing to my other posts. ;^) Nearsightedness and presbyopia: Presbyopia stinks. You get old, you stop being able to focus on things that are close to you. You need reading glasses to read. Or, if you’re already nearsighted, you need to get “multifocial” lens, meaning, at its simpliest, you need two different corrections: a lens to correct nearsightedness to allow you to see far away, and a lens to correct the correction, because your “far” vision now goes TOO FAR!!1!!, that allows you to see near again, but farther than the 6-8” your nearsightedness allows. If you’re nearsighted and wear contacts, you see this just like any normal sighted person. You can see far away with the contacts but, slowly, reading things becomes blurry. You get readers to put over your contacts and the problem is solved. Sorta. If you are nearsighted and wear glasses, one key symptom that tells you you’re descending into presbyopia (well, for me) is that you start moving things under your glasses’ lens. That’s because your nearsightedness still works. Your presbyopia isn’t bad, and there’s really only a very small range of tiny stuff that’s blurry, and you can probably get around this by simply bypassing your glasses. Maybe if your nearsightedness isn’t too bad you can get away with reading with your glasses off. These are signs! Multifocals are near! Types of multifocal lens: Let’s cover the types (and I need to add a few more here later) of multifocal lenses. *Keep in mind all of these multifocal lens types exist because of nearsighted people with presbyopia.* One lens is enough to fix your nearsightedness when you’re young. Then you get prebyopia on top of it and we need to correct twice. Then your presbyopia gets so bad you can’t focus on books and computer monitors with the same lens, and you need three — distance, reading, and monitor/intermediate length fixes. But you can always take your glasses off and see six inches in front of your nose again. Well, most of us. image from Quora progressive lens images (with added label) from Zenni Optical Bifocals: You have one prescription for far vision and another for close/reading vision. I like bifocals b/c there’s one clear line of demarcation where things change and zero lens-induced blurriness, unlike progressives. Types: D-shaped or moon shaped This seems to be common now. The advantage for me is that side peripheral vision is all distant, making walking easier. The advantage for people making the lenses is that they just stick ("ADD") a lens on top of the conventional one to change the prescription. Simple. Executive/straight/Franklin: One line cuts all the way across the lens. The original bifocal. Actually pretty rare now, afaict. Takes a true optician, I think. You don't just paste a lens on top. You're putting to lenses together. Golfer bifocal Glasses mess up my peripheral vision badly enough I can’t golf with them at all, but... Some people have the same issue with bifocals messing up their swing as the change in vision between lenses is jarring. These fix that by giving all distance vision except a small bifocal in the outside bottom of your dominant hand side's lens. Now you can see your scorecard in that window (and only through one lens), but your peripheral vision towards the hole is completely clear. Progressives These are the slick lenses that cost a lot more and don’t have any lines. You look young again! (Ha ha ha. No you don't. Sorry. But your glasses do!) Everything you ever wanted to know about how they work Here’s the key: Progressives expect you to move your head in the direction of what you want to view, not your eyes. They completely discount peripheral vision. Types: Normal three-distance lens Note that the “distance” portion in the pictures above and below is pretty phat. Intermediate or PC distance is super tiny The close up/reading is better, but note all the area without a label. That’s where the progressive trick leaves useless glass. You can’t see out of this part of the lens Advantage over bifocals: You can ostensibly see your computer montior with the third range, intermediate. Advantage over trifocals: There are no lines, so you look OH SO YOUNG. Near-range progressives Sort of two distances, close (reading) and intermediate (computer monitor) Emphasis on the reading. Advantage over bifocals? Reading area is larger than your typical D-shape overlay. DON’T DRIVE WITH THESE “Office" or “computer” progressives Same as near-range, with two distances supported. Emphasis is on intermediate distance. PCs. Advantage over bifocals? You don’t have to tilt your head to see your computer monitor. Trick question: If I had bifocals with intermediate vision in the “main”/top lens, aren’t I doing just as well? Better yet, if I had bifocals with a higher segment line, distance on top, PC distance for the bottom (but now over half of my field), aren’t I doing better? DON’T DRIVE WITH THESE EITHER. THERE’S NO DISTANCE LENS. Progressives stink for computer work. No, seriously. Check out the “blurry area” and the area for “PC” in normal progressives. This is useless. image from Michael Penczek at youtube Here’s a decent but long explanation of why the lens has blurry spots — the “optical swamp” as this guy puts its. I’ve got it cued to showing a trifocal equivalent of a standard progressive where he’s showing how close the three lenses are in the middle of the compound lens, which gives you an idea of where the “sight corridor” (the part down the middle where you can see in a progressive) comes from. How bad are progressives and their crappy “optical swamps”? Bad enough that Nikon has a range of lens that run over $450 to get just the tiniest improvement to that vision corridor. Um… wow? You know what doesn’t have the swamp? Bifocals and trifocals. Bifocals and trifocals don’t have a swap, and can have 100% coverage for intermediate vision. Nearsighted Superpowers: But here’s the deal: You don’t necessarily have to get multifocals when this starts. Because it’s not that you can’t see close any more. It’s that your eye doesn’t allow you to focus on as large a range of corrective distances any more. And here also is your nearsighted superpower: Before presbyopia set in, you could see things that were INSANELY CLOSE!!! I remember getting a hair cut and having a small hair fall into my (skip to the next paragraph if you’re squeamish) tear duct in my eye. When I went to the eye doctor to be sure, he thought I was just guessing when I said that was what happened. But I really could see it in the mirror when I got up close. He needed some serious magnification before he said, “Hey, you’re right!” If you’re nearsighted and probiscus-endowed enough, you might be able to focus on the end of your nose with this super power. Or do watchwork without a magnifiying lens. It is a superpower. But though your range comes in lots closer than an average human’s, it also stops well short of theirs too. So you get glasses, give up your superpower (at least while your glasses are on. Who does this sound like?) and go on your merry way. As you get presbyopia, you lose a little of this superpower. Your range decreases. You can still see clearly 6-8" (or whatever for you) away from your face, but not the end of your nose any more. Still superpowered, don't get me wrong, but the range has diminished. The $7 trick to put off multifocals: With what comes next, please recall that I’m not a doctor, just a middle-aged myopic. Please consult your eye specialists for what’s right for you. And therein is the trick: Your optometrist or opthalmologist corrects based on getting things perfect at 20/20 or beyond. They want crystal clear distance vision. They moved your vision's range from SUPERPOWER CLOSE to eight inches to a normal range of about five inches to INFINITY AND BEYOND. What if, and stick with me here, i wanted to trade crystal clear mountains in the distance for skipping the multifocals? What if I ordered slightly less powerful single focal lenses that allowed me to see my computer monitor perfectly at the expense of seeing the clouds in HD? That is, what if I wanted my corrected range to move from (5" to INFINITY) to (18" to REASONABLY FAR AWAY SO I CAN STILL DRIVE)? Again, presbyopia does not mean that a nearsighted person can’t see close up. Of course you can! Not quite as super-power style close as you once could, but still much closer than the general public. Presbyopic myopics have lost some range in what they can see with single focal corrective lens. You can’t focus as close, which means the range you can focus on with your single focal glasses is constrained. You could probably see to the ends of the earth with good glasses when you were young. Now you might have to trade that for seeing a half-mile out with extreme precision so that you can focus on a computer monitor easily. *And that’s exactly what the bottom half of bifocals do. The give you a weaker prescription* by whatever your ADD value is. You take your negative value for your prescription, -4 or -5.75 or whatever, and you add a value to it — though note that that’s not where ADD comes from. Your bifocal lens is simply a less powerful prescription for nearsightedness. If you had your bifocal bottom lens' prescription in a single focal lens, you could see a lot more of whatever’s close in your visual field in focus clearly. But far away would be a pain. But because you probably don’t need super-close vision, you can get what I’ve seen advertised as “computer glasses” that focus on somewhere between reading (bifocal bottom half) and distance (bifocal top) to bring intermediate sight perfectly into focus. Note that I'm not talking about are not “office progressives” — those are multifocal lens like those on the right side of the Zenni image showing three progressive options, above. These “computer glasses” are single focal lenses that are less powerful than your distance prescription by about *half your ADD.* Zenni Optical describes these sorts of glasses here. When you’re just getting presbyopia, the concession between your full distance prescription and half your ADD is very small. Back up .25 or .50 on your nearsighted prescription (from 5.00 diopters to 4.50, for example) and see how that works for you. You can probably wear them all the time (like I did for a few years — remembering that you might want full correctives or multi-focals for driving) when you’re just starting to lose your range of sight. A place to try this out for cheap: I’ve gotten glasses on the cheap from Zenni Opitcal for years. Zenni has a frame I really like — doesn’t look horrendous, is pretty resilient (some of their plastic frames are crap) — *that’s $6.95 with lenses. No kidding.* With $5 flat shipping per order, there’s really no reason not to play around a little. And since I took the “computer glasses” idea from their website, so they’re game to play with your prescription a bit. I've ordered several prescriptions at once in different frames so I could try a range of different intermediate distance values. So give the “computer glasses,” but maybe with personally tuned partial ADD values, cheat a try. Even though I’m slowly getting past the point that I can use a single precscription for everything I need to see, it postponed getting multifocals for a few years. I also still use them when I’m on the computer, allowing me to see everything up to about two feet clearly, which is perfect for getting work done. It sure beats the heck out of tilting my head up (bifocals -- though admittedly now I'd like to custom order lenses that simply move the line up on bifocals and have distance vision start just over the top of my monitor) or moving that small dot for intermediate vision directly at the spot I want to view (progressives). And when they were good enough for driving too, well, it wasn't bad at all. Labels: Other Stuff, presbyopia posted by Jalindrine at 11/21/2020 01:44:00 PM

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