Are There Blind Spots in Our Eyes? ABSTRACT Our eyes are vital organs because they help us visualize our surroundings. But are our eyes perfect in seeing what’s right in front of us? Sadly I learned in our evolution, nature messed up at one point and gave us blind spots in our eyes. This project shows why we have these blind spots, how to discover them, and how big they are. I researched on how our eyes see things; why when one eye is closed, the other eye sometimes can’t see what’s in front of it. I also found during my research a formula that is used to estimate the size of a human eye’s blind spot.
I performed an experiment using Blind Spot Test card I made to verify the existence of blind spots in my eyes. I also collected data while testing to find the size of my blind spot. I learned the size of eyes’ blind spots varies in relation to the size of the human eyes. QUESTION Are there any blind spots in our eyes? If there are, how do we find them, and how big are they?
If I close one of my eyes, using a test card marked with different symbols then I can find my other eye’s blind spot. Add a ruler/yard stick to take measurements; I can estimate the size of that blind spot too. I think the bigger the human eye, the bigger the blind spot is. BACKGROUND RESEARCH The following diagram shows the anatomy of a human eye (New Translation of Laruelle’s ‘Biography of the Eye’). Our eyes see things when light reflects off the objects goes through the pupil and sends the information to our brains.
The eye and brain work together as a group that after the information gets delivered to the brain as electro-chemical signal, it is interpreted, or “seen”, as images (WebMD). The first layer of our eye is the cornea. It is made of a clear tissue and protects the eye like a see through glass cover. More importantly, it helps the eye focus on an object while light passes through it. The iris, a colorful part of the eye around the pupil behind the cornea contracts or dilates to control the amount of light that goes into the pupil. The pupil at the center of the iris is an opening that lets the light into the eye (Your Eyes).
After light enters the pupil, it passes through the lens behind. The lens functions just like a camera lens so that it focuses the light and beams it onto the retina, the light receptor at the back of the eye. The retina’s surface is flat and smooth, and it acts like a movie screen or the film of a 35mm camera. However, unlike a screen or a film, the retina also has some other features, one of which is the light sensors that detect light. After the retina detects light, it converts the light into electro-chemical signals. These signals then exit the back of the eye via optical nerves and get sent to the brain for processing (WebMD).
There is a little area on the retina where the optical nerves are attached to the eyeball at one end and connects to the brain on the other end. This spot of the retina contains no light sensors. Without light sensors the retina cannot sense light, therefore if light hits that spot, it cannot convert the light into electro-chemical signal and pass the information to the brain to “see”. This forms a blind spot on the eye. The blind spot however, doesn’t affect our vision because our brain “ignores” it. Also having a pair of eyes, one eye can back up the other eye’s blind spot so that we have a clear vision most of the time.
This is why people usually don’t notice the effects of blind spots (Kingfisher 114). There are ways to test human eye’s blind spot. Scientists also discovered formula to estimate the size of our blind spots. Depending on the size of our eyes, we each have unique blind spots.
A cardboard card approximately 3 x 5 in (or 8 x 10 cm) in dimension Black Marker to draw symbols on the cardboard card Ruler/Yard Stick A pencil to record the data EXPERIMENTAL PROCEDURE Often people use the following experiment (Exploratorium), or its variation to test for blind spots existing in our eyes:
Make a test card using the cardboard material. Use a black marker pen to draw a black dot and a cross on the two edges of the card. Make sure the dot and the cross are on the same level. Hold the test card away at an arm’s length and at eye level, while the other hand holds a yardstick just below the left eye. Put the test card on top of the meter stick. Make sure the cross on the test card is on the right hand side. Close your right eye and stare at the cross with your left eye. At this point, you should also be able to see the black dot. Focus on the cross and move the test card towards you by sliding it along the yardstick slowly.
At a certain point, the black dot will disappear from your vision. Record the measurement on the meter stick when that happens. Continue to move the test card forward; you’ll notice the black dot will reappear again. You can also test for the other eye by closing your left eye instead. This time you should look directly at the black dot with your right eye, and as you move the test card closer to you, you should notice the cross disappear and reappear again.
DATA AND DISCUSSION
The following is the formula for finding the size of the blind spot of a human eye: S/m = d/D
In this equation, S is the size of the blind spot on the eye, m is the distance of pupil to retina, estimated by the diameter of the eye, d is the size of the black dot on the test card, and D is the distance from eye to the test card (Exploratorium). Thus, to solve for S, we have: S = d/D * m To perform the experiment, I have two test subjects: my mom and myself. We measured the diameter of each of our eyes as following: my eye is roughly 2 cm, and my mom’s eye is about 2. 5 cm. Then we stepped through the above-mentioned experimental procedure, and wrote down the data.
Experimental Data Black Dot SizeDistance between eye to test card when black dot disappeared Andy Eye diameter = 2 cm0. 25 in ~= 0. 635 cm11. 75 in ~= 29. 845 cm Andy’s Mom Eye diameter = 2. 5 cm 0. 25 in ~= 0. 635 cm13 in ~= 33. 02 cm Based on the data collected, I calculated my blind spot is approximately 0. 0426 cm, or 4. 26 mm in diameter; and my mom’s blind spot is roughly 0. 048 cm, or 4. 8 mm in diameter. Since her eye is slightly larger than mine, her blind spot is a tiny bit bigger than mine as well. I wish I were able to find more test subjects for my experiment.
However, I couldn’t find other people to try the experiment.
In conclusion there are blind spots in the eyes and my hypothesis was correct. The experiment shows there is a blind spot in the corner of our eye because of the optic nerve, and that the size of the blind spot differs from person to person. Our blind spots are an evolutionary defect. Nature was able to correct it by making us have two eyes so we could see clearer and we have a bigger vision field. With that being said we are at the end of my research paper. I hope you enjoyed our little adventure.
I would like to thank my mom, Jane, for being my test subject for my experiment.
“Blind Spot: To see, or not to see”, Exploratorium, http://www. exploratorium. edu/snacks/blind_spot/index. html
“New Translation of Laruelle’s Biography of the Eye”, Fractal Ontology, Nov 21, 2009 http://fractalontology. wordpress. com/2009/11/21/new-translation-of-laruelles-biography-of-the-eye
“The Kingfisher Science Encyclopedia”, Kingfisher Publications, 2006
“Your Eyes”, Kids Health, http://kidshealth. org/kid/htbw/eyes. html 5. “Your Guide to How the Eye Sees”, WebMD, http://www. webmd. com/eye-health/amazing-human-eye
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