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I'm looking at your idea with reading glasses on. If I move the glasses
forward, on the bridge of my nose, and look to the screen over the top
Of them, i.e. straight ahead, everything's a blur. Even when I tilt my
head back whilst looking straight ahead and the bottom third of my
eyes are lined up with the glasses and screen, everything is still out
Of focus. Until I fully focus through the reading glasses, nothing is clear.
Therefore, I conclude, the whole eye is required to make use of the bottom
third of reading glasses and your idea wouldn't work. Having said that, I'm
No optometrist and might be wrong. |
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I wouldn't think it would work that well, but since there are bifocal contact lenses on the market, there are probably people who would shell out for this, were it avaliable. |
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There is an operation for those needing reading glasses already, but it doesn't involve laser surgery. The surgeon embeds a little ring around your cornea to give it something to push/pull against when focusing. I believe there's no reason why you shouldn't have both operations. |
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Like lasik, corneal rings correct vision by flattening the cornea. It can be removed later, if you don't like it, which is the advantage. (I don't believe either help with focusing at different distances.) |
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Kind of like a steel drum eyeball. Hmm. |
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[DrC]: I believe that the cornea plays no part in varying the focus on the fly, so to speak (rather the ciliary muscles alter the shape of the crystalline lens), although a device as you describe can provide a different range of focus by changing the shape of the cornea semi-permanently (ie, when it is fitted, in the same way as rigid contact lenses). |
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wouldn't work. Your cornea/lense would move when you moved your eye. It would stay in the same place relative to your center of vision. |
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Contact lenses behave that way also but, as [ldischler] noted, bifocal contacts are available. I cannot figure it out either. |
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I am not an optometrist, this is just my understanding of how the lenses work, as well as some potential drawbacks, based on the descriptions in [ldischler]'s link. |
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The aspheric bifocal contacts behave by creating a "volume" of focus, rather than a "plane" of focus. With this setup, you can improve vision of someone with particularly poor vision, but nothing will be completely crisp. |
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The concentric bifocals perform similar to regular bifocals, but instead of a single plane of focus, there are two. A "focused" image would be formed consisting of the properly focused image from the selected plane overlayed on the slightly blurred image from the other focal plane. When you look at a particular item, it will be sharply focused, but with a blurry halo around it. |
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The translating contacts have a flat surface on the bottom. This flat surface catches on your lower eyelid when you look downward, keeping the lens stationary while your eye rotates downward to look through the near-focus portion of the lens. Gravity does the rest to pull it back into far-focus alignment when you look up again. There may be a "halo" symptom similar to the concentric lens, but it probably won't be quite as prominent. |
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