We are going to make an eyeball model using a balloon. This experiment should give you a better idea of how your eyes work. The way your brain actually sees things is still a mystery, but using the balloon we can get a good working model of how light gets to your brain.

Materials:

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The balloon itself is the white part of your eye (sclera), which is a protein coating that holds the whole sphere together. The plastic lens we’re going to insert into the throat of the balloon is the lens in your eye. The stretched rubber is the ciliary muscles, which are also a part of the iris, and this controls how much light enters your eye. The back interior of the balloon, where the image is going to appear, is your retina. The retina is where you’ll find the cones and rods that send the light information to your brain.

When the balloon is focused on the candle, this is your normal vision. When you squish the balloon from the top, the image becomes distorted and the focal point of the lens places the image in front of the retina (making the image blurry). This is a condition called nearsightedness. Farsightedness is when you squish the balloon together to make it taller, and the image actually focuses beyond the back of the eye.