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Tunnel Vision by Derrick Boudwin Link

Tunnel Vision written by Derrick Boudwin

Tunnel vision is kind of a bipolar term; it both accurately describes and wrongly defines a lack of peripheral vision at the same time. Let me see if I can explain what I mean.

One of the key signatures of Retinitis Pigmentosa (RP) is a gradual loss of peripheral vision. Usually vision loss occurs from the outermost regions of the eye and moves slowly inward toward the center. This includes the sides of the visual field as well as the top and bottom. So the more vision you lose, the more restricted your field. It becomes, more or less, tunnel vision.

Often people will say that it’s like looking down a cardboard tube. When trying to explain what’s going on with my eyes I have said the same thing. It’s not totally true though. Yes I can’t “see” objects in my periphery technically, but the brain is a marvelous thing! Check this action out.

Vision is a lot like a digital camera. The camera has a lens that focuses light onto a sensor called a CCD. The CCD encodes the image into electronic pulses and sends it to the camera’s processor. The processor organizes the pulses into data on the storage card and then sends an image to the screen. Your setup is almost the same. Your eye (lens) focuses light onto sensitive cells on the retina (CCD), through the optic nerve the image is fed by electronic pulses into the brain (processor.) So your brain is responsible for making sense of what your eye shows it. It decides what an object is, whether to remember it or not, and how to react.

Did you know that you have a blind spot in each of your eyes? Everyone does, but you don’t notice it. The optic nerve sits at the back of each eye and takes up a small amount of space on the retina. So when your brain gets the image from your eye there’s a small hole in it. You don’t notice it because the brain makes an educated guess on what should be in the hole based on what’s around it and what the other eye sees. Think retouching a hole in a photo, only hundreds of times a second.

What I have noticed, and corroborated with other similarly blinded people I know, is that when the vision starts to fade from the edges, the brain just fills it in. You might have moderate periphery loss and not even know! How do you find out? Usually you start to notice something is amiss when the brain fills the image in wrong. For instance you are walking down a sidewalk with grass on both sides, that’s way easy for your brain to draw. You’ve seen that image thousands of times. You see it as you always have. What you might not have seen is a person walking across your path from your blind side. Since your eye didn’t get an image to your brain of that person before he walked into your useful vision-it was too late, you hit him. You don’t know what happened, and the person might think you are clumsy or rude. (In lieu of person feel free to insert: pole, hole, drinking fountain, or door frame)

If an image starts off in your central vision, your brain will continue to draw it even after it moves into your blind spot. It doesn’t get ghosty or faded either. If a person walks past you on the street, you will continue to see them walking past you. I mean legs moving and everything. Your brain knows what a person looks like walking, why do you think dreams can seem so real at times? So this condition, from central to blind spot isn’t too much of a problem; although it can be interesting if you are talking to someone in your blind spot and you turn to see them disappear. Yeah, they probably left a long time ago, but your brain didn’t get that info, so it just assumed they stayed put.

Objects moving from your blind spot to your central vision are a whole other game. This is what makes driving especially dangerous. Picture your ride home. You can see clearly in front of you. You see the car in front of you and the cars passing you headed the opposite direction. Everything seems normal. Meanwhile a car starts to pass you on your left hand side; since you don’t have any vision there your brain continues to draw what is in front of you as it passes you- an open lane. The car continues to pass you until finally its nose pokes into your useful vision. Suddenly there’s a car there! It’s startling and scary. If you had decided to move into the open lane, you would have been grossly disappointed. The last day that I ever drove this happened to me twice. I never had a close call, just all of the sudden, where I saw was open road- a car just appeared. I knew it was time.

So next time you’re getting or giving the cardboard tube analogy- don’t forget how smart that brain of yours is.

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