What’s up with contact lenses?

ken writes:

Dot and I took a trip into town today, with kids in tow, to have our eyesight tested. Surprise! My eyesight has actually improved. I used to be -8.00 in one eye and -7.75 in the other, and now I’m -7.5 in both. The optometrist speculated that it was due to my not spending so much time in front of a computer. So hooray for recession and under-employment!

Dot bought some new glasses but my glasses still cover my prescription so just got my current specs tightened up and bought a few pairs of contact lenses. I’ve had them before but that was about eight years ago. Here is my question about contact lenses:

How come everything looks bigger* when you wear contact lenses?

Of course it is just something to do with the different ways contacts lenses and spectacles bend the light. With spectacles there is a slight distance between the lens and your eye that isn’t there when you’re wearing contacts. It’s like the illusion of the wing mirrors when you’re driving. Objects in the mirror appear further away than they really are. Blah blah blah. I’m sure that’s all correct.

What I don’t understand is how a global change, which affects everything you see, could make a difference to your perception of size. Things look further away in the wing mirror because objects in the mirror look smaller than they appear when you’re not looking in the mirror. You can make the comparison because you can look (over your shoulder) at the same object not in the mirror. You make a comparison between the mirror life and real life. But when you put contact lenses in, everything is seen through the contact lenses so there’s no equivalent comparison.

How can everything get bigger? Does that mean the distances between the objects get smaller? Suppose you draw some figures on a piece of paper. If you make all the figures bigger, won’t that involve making the gaps between the figures smaller? To keep the gaps the same and grow the figures you’re going to need a bigger piece of paper. Does that mean putting in contact lenses is like getting a bigger piece of paper? I don’t think the illusion is accompanied by the feeling that distances are smaller. You don’t find yourself reaching for something and find it not where you expected it to be. In my experience that’s not what it’s like. The gaps don’t seem to get smaller to accommodate larger objects, so does the visual field somehow get larger? But how? All you see is still ALL YOU SEE. You can’t get bigger than everything.

I’d be interested to know how people think the illusion works.

* Or smaller when you wear glasses?


5 thoughts on “What’s up with contact lenses?

  1. Katimum

    I have just been experimenting with binoculars, which I suppose do a similar job to glasses/contact lenses in bringing into focus far away objects. If you move the glasses away from your eye, so your field of vision reduces. Wearing glasses means that your effective area of vision is restricted to the area of the lens, with the brain discounting the periferal area round them, but the surface of the eye ball becomes the lens with the contact lens, so you get the whole area in use. I am facinated by the thought that we actually see upside down and the brain neatly flips the image – unless we wear glasses which already flip the image for a period, in which case the brain learns to unflip. I wish I could remember those neat diagrams about lens and eye focus I did in ‘O’ Level Biology though.

  2. Laura

    Isn’t this a case of parallax displacement? Even though the eyeglasses are mere mms from your eye, there is enough room to create the effect. Try moving the glasses down the bridge of your nose then back up as near to your eyes as possible. Doesn’t close magnify “the world” slightly more and glasses far away diminish things?
    ‘Looks’, heh…

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