Why most people don't wear glasses in optical center

When buying glasses we are told to match them with our pupillary distance so that we can see through the optical center. but why most people wear glasses not on optical center, like the image I searched on google below

images - 2020-10-04T120328.937 images - 2020-10-04T120449.703 images - 2020-10-04T120543.919
optical-center-glasses

their pupils are slightly to the side of the optical center of the glasses. why are their pupils not at the optical center?

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The optical centre doesn’t mean the centre of the frames. It refers to the shape of the lens.
If it were based on the centre of the frames, then you PD would determine with frames you got to chose from.
The PD tells the optician where in the frames to put the centre of the lens - the “centre of the lens” being the centre before it is cut to the shape of the frames.

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thank you for your description. I have been confused about the optical center on the glasses. I also watched your video and saw when you were wearing your glasses and I was confused why your pupil is not right in the middle of the frame. it turns out that the optical center is not always in the center of the frame

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:+1:
Yeah - a bit of a hazard buying online - the glasses can be quite a bit bigger than you expect XD
Luckily it doesn’t effect how well the glasses work.

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Correct vertical center of lenses is also very important, especially with higher diopters.
Though, many opticians neglect that for some reason, maybe because (very) high myopia is not so prevalent for now.

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But where your eyes are looking vertically would change a lot depending on where your glasses sat on your nose, and whether they had slipped down, how the nose pads were adjusted, whether you were looking down, up or straight ahead.

I can see why vertically the centre would be simply placed in the vertical middle of the frames. Far too many variables to make measuring it valuable. Whereas if the horizontal is off, you can never see properly with both eyes at once. The horizontal measurement is from one eye to another. Vertically, there is no other eye to ensure it is the correct distance from.

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This seems to be the biggest and constantly changing variable. How much of the time is anyone looking through the same part of the lens outside of screen use?

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If your PD slightly different . Then what will hapened ?. It can cause of astigmatism? Or axis

double vision. lots and lots of annoying double vision

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Does moving the eyes left and right feel uncomfortable in general? I think it does to me. I’ve noticed that with glasses I tend to move my head left and right rather than scan with my eyes, which deprives the brain of a very important anxiety-relieving mechanism (lateral eye movement). I think I also got some astigmatism by reading while laying (lying? English enthusiasts help) sideways looking through the wrong part of the lens. Though according to functional astigmatism theories it’s likely that that posture itself could cause astigmatism and the glasses only provided the hyperopic defocus to speed it up.

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Yeah, Jake has spoken about this somewhere too, if I remember correctly. People with glasses are more likely to move their head to look around than their eyes.

Good point! I hadn’t thought about that element.

lying sideways.
You could lay your book down,
but you are lying down.
“Laying” is more an action taken on something else.
“Lying” is something you can just do (although, hopefully you don’t do so in every sense of the word. XD).

Would you like to provide any further input, @Ursa?

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Except in the old-fashioned phrase of ’ as I lay me down to sleep’. You have the basics, and I won’t bore people with transitive and intransitive verbs. :grinning:

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Only white lies :smiley: thanks for the explanation!

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Oh, good example, @Ursa! Then the thing you are laying down is “me”. Still has a “doing it to something” vibe (so a transitive verb in that case anyway :wink: ).

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How do you know where the optical Centre is on those lenses in the images? The answer is :you don’t. It can be off to the side and does not have to match the spatial centre of the frame eye

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Usually slightly above center.

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