Why do I need glasses?

Greetings! I feel inspired to write this post for a couple of reasons. For one, I’ve had recent conversations with a number of my friends concerning the wearing of glasses–some of them don’t want to wear them because they “look bad” or because they don’t want to look “nerdy”, while others just think that their vision is “good enough.” Regardless, the eye is a fascinating organ, and the reason for glasses is something many people don’t actually understand. And personally, I like wearing glasses…they make me look smart, and my visual ego will take all the stroking it can receive.

Anyway, to understand the eye, one must know about the (arguably) exciting branch of physics known as Optics. Optics deals with light–its properties, behavior, etc.–and since the eye is just a light sensitive organ, the two go hand in hand. The eye is actually like a camera for our brain. Light passes through a lens located at the front of the eye, and (ideally) converges the incoming light at the retina. The retina serves the same purpose as the film of a camera (or for a digital camera, a CCD chip): light hits the retina, creating a 2D version of the world around us, which cause electrical impulses to be sent to the brain via the optic nerve. The brain interprets those impulses and creates the world that we see. With one eye, it would look just like a camera’s image, with the depth being inferred by our knowledge of the world, but not actually seen visibly in the photograph. However, because we have two eyes, our brain is constantly receiving two different images at slightly different angles, and can interpret the two to create a 3D world. Thus, people with one eye, or who cover one eye long enough time will have severe problems with depth perception (so stop blaming your bad driving on your terrible depth perception–you have no excuse!).

All lenses, including those in your eye, bend light in ways depending on the shape. The lenses in your eye are convex, shaped a little like a small cigar. Convex lenses, also known as converging lenses, take incoming light and converge it at what’s known as a focal point, the place where all light beams meet. It is at this focal point that a focused image is created. If you look at an object through a converging lens, unless the image screen is placed at the focal point, the picture created will be blurry. We’re now approaching how you explain Myopia (nearsightedness) and Hyperopia (farsightedness). The lens of the eye has to converge light from the world onto your retina. It cannot focus the entire world at once (it’s easy to notice when you focus on a far away object, and then immediately focus on, say, your hand–your eye has to increase its focusing power to see your hand clearly), and so the eye adjusts the lens to allow you to focus on that which you are looking at. However, sometimes, it is unable to focus on either close objects (Hyperopia) or far away objects (Myopia). If the eye’s lens is unable to focus the light on your retina, the images become blurry. In the case of farsightedness, you cannot focus on nearby objects, because when you try to, the image converges behind your retina. So how do you correct it? You wear glasses, or “corrective lenses”–these lenses are converging, and shift the focal point to your retina.

So that explains farsightedness and its corrective lens solution…but what about nearsightedness? Well, people with Myopia have the opposite problem–when trying to focus on far away objects, the focal point of the lens falls short of the retina, and needs to be shifted backwards. This is done using a concave or diverging lens. This type of lens is shaped like an hourglass, and causes light beams to be scattered away from each other. Then, the light beams get converged by the eye’s lens, and voila, the focal point is pushed back onto the retina. Focused images!

 

And so, I have (hopefully) demonstrated the cause of bad eyesight, and why glasses are a necessity for many people. Of course, contact lenses work too, it’s just that they are directly on top of the eye, hence contact¬†lenses. The correction without¬†sacrificing the “cool.” I don’t know, I’m a four-eyes and proud of it. So if you have bad eyesight, please get some glasses! I’m looking at you, my nameless friends.

Before I go, I want to shamelessly plug my friend’s blog. A while back, my good buddy Alexandra Greenbaum wrote a guest entry about building a science comic. Well, she has been inspired by me and our other good buddy Vivienne Baldassare to create her own blog, entitled All of the Above. This blog is all sorts of awesome, and I encourage all scientifically minded readers to bookmark her blog for further reading! She’s also got some great cartoons and is likely to update more often than me, so yeah, check it out!

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5 Responses to Why do I need glasses?

  1. Mike Young says:

    Thanks for a great entry, Dan!

  2. I automatically looked for alt-text when I saw the pictures; is that bad?

    I likes this a lot! I know this is going more in depth than you probably intended, but have you ever looked into/learned about astigmatisms?

    • Not bad at all. I hoped for people to notice the first alt text at the very least.

      More in depth for the post, maybe, but astigmatisms are also interesting. From what I remember, they are scars or scratches on the eye? I think those were more complicated problems than myopia/hyperopia and require more innovative solutions than the ones mentioned here, but the idea is similar. They make you have blurry eyesight because of an inability for the eye to focus the light on the retina.

      • I think there’s a sort of astigmatism that is caused by a scar or scratch, I’m not sure though.

        I was thinking of the very common corneal astigmatism, where the cornea is irregularly shaped; think of a normal eye as ping-pong ball shaped; an eye with an astigmatism would be football shaped, so it results in a refraction error (and football shaped contacts).

  3. BudB says:

    The conventional astigmatism is all about eye shape. I have had this problem since middle school, but only got around to getting glasses in high school. If you are ever in the Montgomery area, you can contact this site for some help.

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