🎥 Video: Use Cases For Bifocals

Some types of occupations and hobbies have a high requirement for both close-up and distance vision in the same time spans.

So two pairs of glasses there aren’t very practical.

In these specific cases I sometimes suggest trying out bifocals - but not progressive lenses.

After only about five years or so, finally got around to making a video explaining why:

(not sure if I’ll ever stop feeling ridiculous making videos and posting them on the Internet - definitely too old for the current generation of humans)

Pretty simple and as always goes right back to 1) minimize focal plane changes and 2) simpler is better.

And as usual I make these videos based on a comment or e-mail that specifically rings a bell that there’s a topic in neglect of clarification. So anytime you think of stuff that ought to be covered, feel free to nudge me about it.

Also as pointed out in the video, I’m not entirely 100% completely infallible (the heresy!). Most of the things here as usual, based on collected experiences rather than some sort of facial protein filament based innate genius. Always possible that some particular cases will entirely benefit from progressive lenses. Feedback and ideas and experiments always most welcome.


I think you are pretty good at it at this point :slight_smile: You first few video back in 2015 was… well, not talk about those :smiley: (but they still has a lot of valuable information) But you got better really fast, and I would say I really enjoy your videos from the last year. And I was one of the guy who preferred your blog posts: well, not anymore :slight_smile:


Caveat emptor! We have no idea how this even works.

Remember: the eye doesn’t give a damn what you look at. The calibration signal comes from peripheral vision.

Bifocals are causing perverse amounts of hyperopic defocus while you use them for near work.

Yes, usually, with bifocals, it looks like the eyes don’t care. Any way of wrecking the peripheral image during near work appears to help to diminish the stimulus for elongation, even hyperopic defocus if it’s extreme enough. But there’s something uncanny about messing with signals without any understanding of what effects they have and why.

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But there’s something uncanny about messing with signals without any understanding of what effects they have and why.

For sure. Though lacking “any” understanding of effects may be a bit under-crediting. I wouldn’t put out things that are entirely unfounded in terms of effect to the entire audience base.

For testing I approach most of these things in a very highly ethical (and yet practical way):

What will happen? Hey look, there’s a bunch of free guinea piggies over here! :smiley: If a thing works for somebody, let a few other people try it. If it works for them, share with a slightly larger group. Look for holes in expected outcome. Expand till we know where the limits of any given piece of all this is.

It’s not extra glamorous or rigorously scientific for writing papers - but then I started this whole eyeball caring about only one thing - getting my 20/20 eyesight back. I only looked at data to the extent that I needed hints of what to try next. I wasn’t ever interested in the how and why so much, as getting those damn things off my face. Then when something actually worked, eventually the question came around trying to explain the ‘why’.

In looking at a life of limited resources (time mainly), my needs make me a bit of a terrible hack in many ways. I only take things as far as practically necessary. The great news is that the whole thing has grown large enough to where my hack-ey ways aren’t all there is (in no small part thanks to contributions like your own especially).

When it comes to the bifocals, indeed you’re for sure right about defocus. And I don’t recommend them in general AT ALL (as mentioned in the video). But there are cases where that’s the compromise, having two focal planes. It’s that or full correction / distance glasses full time basically (with a lot of cumulative close-up), and bifocals in practice work out better for that scenario. A bit messy but it can get the job done.

Cool part about having a ton of practical insight on results is that it should give a lot of context for further researching why the things that actual work, do so.


Absolutely! I really value your input, and it hasn’t failed me so far. I have the impression that your observations are largely correct, and we’re mostly limited by struggling with why-questions, the answers to which should make it easier to predict what happens in unusual situations.

For bifocals, I’m just a bit worried that people decide to use them for the wrong reasons. Especially, thinking “I’m looking through this part of the glasses right now, so that’s the lens power I’m using” just isn’t right at all, since parts of the field of view see something thoroughly weird when using bifocals. Since we lack detailed analyses, bifocals could have unintended consequences we don’t know about, like stimulating the eyes to become uneven.


For bifocals, I’m just a bit worried that people decide to use them for the wrong reasons.

No doubt. Many people’s favorite past time is trying to find THAT ONE WEIRD TRICK part of endmyopia, the magic shortcut to fix their myopia. And any kind of multi-focal lens solution comes up pretty regularly as part of that (oh maybe I just won’t buy two pairs, just do x instead).

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I’m just gonna comment here so that this post be “up”-ed again. This (bifocals) can be a solution for students in class. Seriously, the hours students sit and write in class…you know how it’s like :grin: Even after years I’m still glad and thankful I’m out of school now :sweat_smile: