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September 11, 2006 12:08 PM   Subscribe

Can I correct my vision by wearing sign reversed contact lenses?

I messed up ordering some daily disposable contacts off the internet and reversed the sign. I use -2 and -1.5, but accidentally ordered +2 and +1.5.

I didn't notice anything until I put the lenses in, whereupon everything got really, really blurry. My first thought was one or both of the lenses was messed up or I'd reversed them, so I pulled both and put in a new pair. Same result. It was only then that I noticed my mistake.

Well, the vendor won't take them back as the package was opened and I can't really blame them as this was my fault. But I had an idea - would wearing these lenses gradually correct my vision?

I'm a banker and don't know much about optometry, but it sorta seems logical to me, as I envision a number line. And I wouldn't have to lose out on my entire investment in lenses (yes, I am frugal).

GalPal is appalled at my theory, and has hidden the lenses. Can you help me get them back?
posted by Mutant to Health & Fitness (19 answers total) 2 users marked this as a favorite
 
Nope, but they make lenses that do this by reshaping your eye. You wear them as you sleep and the effect wears off pretty quickly.
posted by damn dirty ape at 12:12 PM on September 11, 2006


No, no, a million times no. If it was that easy why wouldn't everyone be doing it already?
posted by xil at 12:14 PM on September 11, 2006


No. Your thinking on this makes absolutely no sense whatsoever.

There are orthokeratological contact lenses that work to correct your vision by gradually reshaping your cornea, but they're rigid lenses that need to be custom-fit by a professional.
posted by mr_roboto at 12:14 PM on September 11, 2006


No, but you can give yourself a big headache.
posted by witchstone at 12:22 PM on September 11, 2006


Now wait a minute! Think number line

+2-----------0-----------(-2)

My defective vision is on the right (-2). Perfect vision is in the middle (0). The now hidden lenses are designed to correct vision that is found squarely to the left (+2) - while you wear the lenses. Why wouldn't they pull my uncorrected vision towards zero, perhaps after wearing them?

Maybe my thinking doesn't make any sense, but could someone who knows about this please explain past the No! part?

FWIW, I already noticed the headache, and GalPal gave me an earful as well after I stumbled about the flat conducting my experiment (a frustrated "BLOODY HELL" was heard).

I just wanna understand why? Also, I'm still not convinced that if I wear them for a little while every day my vision isn't going to improve...
posted by Mutant at 12:35 PM on September 11, 2006


They don't "pull it towards zero" they put it at exactly where they should be if you needed +2 correction, i.e. too far in the other direction. Think of when you use a microscope or magnifying glass -- if you push in too close the image is blurry and if you pull out too far it's also blurry. In order to see a sharp image you need to hit it right at the point in the middle. Right now with your vision you have the knob turned too far one way, and putting in the wrong lenses just causes you to go to the other side of blurry.

It is true to some extent that your eye can compensate for blurry vision, but it does this by flexing muscles in the eye and you can't expect a muscle to just stay in a constant state of flexation forever. That is why you get headaches, as you eye is trying to compensate but the muscles are tired.

I don't see what kind of logic you can posess that makes you think that wearing the wrong contact lens would cause a permanent change in your vision, but as has already been said if this were possible don't you think people would have done it a long time ago instead of sticking these little plastic discs in their eyes for their entire lifetime?
posted by Rhomboid at 12:45 PM on September 11, 2006


I like your theory. The effort needed to make sense through the wrong contact lenses, it seems to me, should strengthen the muscles of the eye in the right direction. Like any other exercise it will need time. Why not give it a try, a couple of hours a day for a month?
posted by londongeezer at 12:59 PM on September 11, 2006


God damn this is a bad idea.

Here's an explanation using your scale idea.

+2----0----(-2)
To get your +2 to zero, you subtract two, right?
Now, your evil twin, with -2 vision, needs to have his corrected down to zero as well. His contacts have a prescription of +2 to get back to zero.
You: (+2 eyes) + (-2 contacts) = 0.
Twin: (-2 eyes) + (+2 contacts) = 0.
Now, you've ordered your twin's contacts:
(+2 eyes) + (+2 contacts) = +4.

Your vision is father than zero than before! You'll be taxing your eyes even more than normal because they'll try to focus back to 0, which is harder to do at the +4 rank than the +2 rank. Headaches galore, and a chance to screw up your eyes even more.

Honestly, I don't know who GalPal is, but I hope she gives you a smack for this terrible idea.
posted by boo_radley at 1:03 PM on September 11, 2006


Simply put, your eyes contain lenses that refract light, allowing an image to be focused on your retina. A near-sighted person (such as yourself) has a defect that makes light focus in front of the retina, rather than on it. This means that objects far away will look blurry. You need a diverging lens (negative power prescription) to correct your vision, making the light focus further back, on the retina.

A person with a POSITIVE 1.5 or 2 prescription would be far-sighted. This means that their eyes naturally focus light behind the retina, making objects close up more blurry, but allowing them to focus at objects further away. The converging lens they are prescribed by their eye doctor will allow light to focus closer in, that is, on the retina rather than behind it.

A decent description of how this all works is available over here: http://www.eyeglasslenses.com/content/knowledgebase/kb_eyeandlenses.asp

Since you are near-sighted, all a converging lens is going to do is just make your vision even 'more near-sighted' if such a thing can be said. Wearing the wrong kind of corrective lens is not going to change the shape of your eye, no matter how much you might wish it could.

Disclaimer: I am not an eye doctor. :)
posted by nyxie at 1:04 PM on September 11, 2006


Why wouldn't they pull my uncorrected vision towards zero, perhaps after wearing them?

Because of how your eyes are broken, unless you're very special.

It's not like your eyes need exercise or something. If they did, then, sure, it might help to make them work real fuckin' hard for an hour so that they'd be all ripped and buff and ready to focus like a motherfucker.

But they don't need exercise to strengthen the muscles. They're just the wrong shape. And normal contacts, especially soft ones, won't do anything to the shape of your eye. They make contacts for this, and RGP lenses have some effect on eye shape, but not soft ones.

With proper lenses, you have wrong-shaped -2 eyes and lenses that correct for that.

With these lenses, you have wrong-shaped -2 eyes and lenses that make it even worse. If you wear them all the time, still have wrong-shaped -2 eyes.
posted by ROU_Xenophobe at 1:06 PM on September 11, 2006 [2 favorites]


No, you have -2 because your eye lenses (natural, not the contact lenses) are shaped a certain way, causing images to fall in front of the retina, making it blurry. You can correct your vision by using an additional lens (contact or glasses) to direct light to fall on the retina properly. Those are the minus lense for nearsighted people, and these shift the image further to the back of the eye.
Farsighted eyes (same link) are out of focus because the image falls behind the retina. To correct that, you need + lenses that shift the image forward, placing it on the retina.
If you are already nearsighted, and use + lenses, then the image will beshifted even further away from the retina. This is what you noticed when you put the lenses in: it became blurrier.

This is ALL lenses do. They are not changing the shape of your eye, which causes the problem, they are just optically correcting what you see to make life less blurry, and your eyes don't really adapt to it.
However, I've heard that if you use hard contacts, they kind of push on your eye and can change the shape that way, chaning your vision, but this is entirely unrelated to + or -.
posted by easternblot at 1:15 PM on September 11, 2006


So I think the logic here is that if you put up with the horrible headaches of +4 vision, then the blurryness of +2 vision when you take them out might not seem so bad, kind of like how you use a bat weight in the on-deck batters box. But I really don't think it works that way, the muscles in your eyes can only affect the focus to a limited amount and purposefully making them work even harder just won't do anything. Why not just put in the correct contact lenses so that they don't have to work at all?

By the way, I seem to recall that there was some famous author or celebrity of the last century who got convinced that he could self-correct his vision by daily exercise and careful thought, kind of like how the poster here is suggesting. He had convinced everyone that he had trained himself to be able to see perfectly without his glasses, to the point of giving some demonstration, but in fact it turned out that he had to use notecards or some kind of cribsheet because he hadn't actually changed his vision at all. It was quite embarassing to this snake oil method of being able to actually affect permanent change on your eyes through non-surgical means. I am sure I am misremembering some details here but maybe someone remembers the actual person and details.
posted by Rhomboid at 1:22 PM on September 11, 2006


You can't just add the lens numbers. The "power" of your lenses is actually an inverse quantity, a diopter, that represents the reciprocal of the focal length of your eye, expressed in metres. And there are real and virtual quantities (plus and minus values) to consider. That is why you can't just flip the lens around. Minux power lenses are diverging, plus power lenses are converging.

A -2.0 lens, for example, has a focal length of -0.5 m.

What's going on in your eye is that your muscles can no longer contract strongly enough to stretch your lens and adjust its radius of curvature so that the rays from far objects are focussed onto your retina. They focus too soon, and then spread apart leading to the characteristic blurriness.

The negative diopter lenses are diverging. They take the incident (mostly parallel) light rays from distant objects and spread them apart a little so that they end up focussing on your retina. They do this by creating a virtual or imaginary image of the distant object at a closer distance that you perceive.

All this process is summed up using geometric optics as the equation:

1/f = 1/i + 1/o

where f is the focal length, i is the image distance, and o is the object distance (taken to be "infinity"). In your case, for your -2 lens, assuming your eye is a standard 2 cm wide, then your -2 lens is forming a virtual image 50 cm away from lens. This is the "far point" of your vision, that is the furthest distance your eye can focus clearly with reduced muscle strength.

You end up with 1/f = -2 = 1/i
posted by meehawl at 1:26 PM on September 11, 2006


Ah thanks much guy! Now I understand!!

"...I don't know who GalPal is, but I hope she gives you a smack for this terrible idea."

Well, she wasn't impressed by the idea either, so my lenses are already in the rubbish I fear. Or they definitely will be after she reads this. I'm shite at optometry, but actually pretty good at making money though...really!
posted by Mutant at 1:51 PM on September 11, 2006


http://health.howstuffworks.com/eye6.htm

read this and the next two pages for some good explanations, and from there I'm sure you can draw your conclusions as to why it won't work.
posted by defcom1 at 2:11 PM on September 11, 2006


stick with banking, i don't think you have a career in optometry.

when i was 5, i was diagnosed with a lazy eye and that IS a muscular problem that can be treated, somewhat, with exercise. basically, you wear a patch over the good eye, forcing the bad eye to get to work. after about a year of pirate jokes (slightly traumatic for a tot) it's mostly corrected though a professional can still pick it out.
posted by otherwordlyglow at 2:54 PM on September 11, 2006


easternblot said:
However, I've heard that if you use hard contacts, they kind of push on your eye and can change the shape that way, chaning your vision

I use hard contacts, and I'll vouch that they have a little bit of residual effect. After I take them out, my vision is noticably worse, but not quite as bad as it is when I wake up in the morning (after sleeping with them out). The effect is pretty minimal, though - I'm still blind as a bat without them.
posted by chrisamiller at 4:28 PM on September 11, 2006


With these lenses, you have wrong-shaped -2 eyes and lenses that make it even worse. If you wear them all the time, still have wrong-shaped -2 eyes.
Your eyes may even get educated stupid!

Oh, come on, I can't have been the only one who thought of it.
posted by scrump at 5:10 PM on September 11, 2006


I thought of rolling up a new Dungeons and Dragons character, to be honest.
posted by boo_radley at 1:06 PM on September 12, 2006


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