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Why don't optometrists correct to 20/20 individually on both eyes

I'm baffled on why don't optometrists correct to 20/20 individually on both eyes. what I mean is that with my glasses on, if I cover one eye and see through the other I'm not getting a 20/20 correction. If I see through both with the glasses on I do get a 20/20.
I've asked but still, the answers are not reasonable.
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Avatar universal
Just thought I might add the following to what Dr. Hagan has said, partly to illustrate it and partly to give a slightly different angle.

Because I have developmental amblyopia, my brain is permanently wired since I was a child for a maximum of 20/120 in the left and 20/200 in the right eye. That's just the way it is. My eyes don't have a lot of potential for detailed vision.

You could certainly get me to a level of vision enabling me to see the 20/20 line on a Snellen eye chart, though. You could achieve this by permanently clipping a monocular onto my glasses. However, doing so would compromise my field of vision so drastically that I'd only be able to pick out a tiny fragment of my environment at any one time. So yes, you could certainly get me to 20/20, but it wouldn't be a terribly useful 20/20.

Glasses and contact lenses are always going to be a compromise involving certain trade-offs, particularly with eyes that have somewhat limited potential like mine. Because I'm aphakic (no intraocular lenses), I need plus lenses for correction, so wearing glasses actually gives me better acuities than contacts because of the slight magnification effect of having a very strong plus lens a certain distance away from my eye (as opposed to sitting on the cornea). The trade-off is a worse field of vision than I'd have with contacts. For many years I wore contacts and accepted the worse acuity because I enjoyed the better field of vision. Nowadays I wear glasses as I prefer the slightly better acuity and don't mind the worse field of vision quite so much.

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Yes thanks for adding this scenario to the mix another is if the eyes are not straight (strabismus or squint) in an adult and giving full correction to the non-fixating eye would make the image so clear that the brain would be aware of double vision.
177275 tn?1511755244
If 100 people buy brand new Nike running shoes at say $250 apiece then line up and run a quarter of a mile they won't all finish at the same time.  Some may not finish at all, some might not even be able to run or walk at all. It doesn't mean there is anything wrong with the shoes its the health and ability of the person wearing them that differs.    Thus trying glasses on a blind eye doesn't help lie new shoes on a person that can't walk or run won't help.  For the people that finish if they don't finish first it doesn't mean something is wrong with their shoes, they don't have the running talent or training or strength of the first place finisher.   If you map out how they finish you will bet the familiar Bell Shaped Curve assuming these people were picked at random.
         Vision is distributed the same way. Although we speak of 20/20 as normal it is really an average of a large number of people.  On the better vision side there are people that with and/or without glasses can see better than that i.e. 20/10 or 20/8   On the not as good side there are people with normal eyes with or without glasses that can only see 20/25 or 20/30 because that is as strong as their normal eye is.
       You would not expect to buy running shoes and be able to go to the Olympics and win the 100 meter dash.  Variations in human ability are the basis of almost all sporting events.  Many human eyes have both normal intrinsic variations and abnormal pathologic variations that prevent glasses from making them unable to see 20/20.
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The other part of the question shouldn't have to be explained to you. If one eye is poorly sighted and best vision is 20/200 and the other is normal and sees 20/20  with both eyes the vision is 20/20 with the bad eye covered the vision is 20/20 and with the good eye covered its 20/20.   Some eyes 20/20 with each eye but with both eyes see 20/15 which is better because almost all of us see better using 2 eyes rather than one. Like a rock you can't pick up with either hand but can easily with both hands.  
Avatar universal
Mine does
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177275 tn?1511755244
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