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About that Squinty Eye(This is an opportunity to do some interpretation.
There are some hands-on experiments you can do below.)
Robert's Experience with Amblyopia
My purpose here is to share my experiences, not to provide advice. So if you have found your way to this web page because you need some medical information, I suggest that you talk to your family doctor and visit some of the sites on the web. Here are some references to begin:
When I was young I learned that they called my condition a 'Lazy Eye' or 'amblyopia.' My parents told me that in 1947, while I was attending the Elizabeth Ballantyne Nursery School, the teachers said I could not see the pictures on the wall; and that I should see an eye doctor. I was almost blind in the right eye.
Dr. Benjamin Alexander, in Montreal, treated me by putting a patch on my good eye to force my right eye to learn how to see. I am also farsighted so I had corrective lenses for both eyes. I enjoyed the many visits to Dick Taylor's optical shop on Ste. Catherine's near Peel Street. Dick was a big friendly man with a booming voice. The optical factory was fascinating place in the back of the store.
Today I can see with the right eye, but not well. With glasses I can read only if the type is large. I see in colour. The problem seems to be a lack of resolution. I have no problem seeing with my left eye which requires correction only for the farsightedness that is exacerbated by my age.
Most people use both eyes and integrate the scene before them. I don't. My left eye does all of the real seeing, and the right eye seems to fill in the peripheral vision. So I am suppressing the vision in the right eye. My peripheral vision in both eyes is excellent, and I probably have the same panoramic sense of my surroundings as you.
There seems to be no problem with the right eyeball. Since my brain is receiving input from that eye some of that information is being rejected. The effort to ignore that information may explain why I am squinting ‚ it may be a mechanical way of rejecting that view. My wife says that she can tell how tired I am by the level of the eyelid.
If I demand the full image from both eyes, I will see double. I can do that with a mental effort. The image from the right eye appears displaced to the right and somewhat above the image from the left eye. On occasion, when I have become very fatigued, the left eye stops providing all input. Suddenly I find I am having trouble seeing as I am receiving only the input of my right eye. Inside my head, it is not evident what has happened. I have learned that the remedy is to use my hand and block my right eye. That turns on the left eye again.
For me, stereo vision is almost as mysterious as colour must be to someone who is colour-blind. So, I have tried to explore what I see, and what you, with two eyes must experience.
Some Experiments in Vision
The Portable Blind Spot Finder
This is my portable blind spot finder experiment:
- Bring the heels of your hands together and unfold your index fingers so they are pointing forward.
- Move the index finger tips apart so they are separated by about 4 inches (10 cm). Since your hands are still folded you should be able to maintain that gap between the tips as if they are calipers.
- Close your right eye.
- Hold your hands about 18 inches (45 cm) in front of you.
- Look directly at the tip of your right index finger with your left eye.
- Slowly move your hands toward your face. Keep your index fingers level, and keep your left eye looking at the tip of the right finger.
- Here is the hard part. While looking at the right fingertip approaching, watch the left finger tip. (No, don't look in its direction.)
When the right fingertip is about 14 inches from your face (35 cm) the left fingertip will vanish. This will take some practice because your brain will try hard to keep something from deliberately slipping into the blind spot.
Using your fingertips as a Portable Blind Spot Finder means that you can explore the world around you to see how your brain fills in the spot where you are really blind. For example, if you look at the 'L' on your computer keyboard with your left eye you will not be able to see one of the keys on the left side of the row, probably the 'S'. Actually you will discover that only the centre of your vision provides a clear image, and that the keys around the 'S' are fairly blurry. You will also find that if you are paying attention to something that is about to slip into the blind spot your brain will attempt to prevent you maneuvering that object into the blind spot. Doing these experiments may take some practice.
Now, what do you think you would see if the tiny bright spot from the bulb of a penlight was shining at you from across the room, but was shining directly into your blind spot? (Either try it yourself, or drop me an email and I will describe what I saw.)
Right Angled Mirrors
Here is a situation where you (with your stereo vision) and I have a very different experience. Find or make 2 flat mirrors that meet at an inside corner of 90 degrees. You may see this arrangement in the back of bars, or in department stores. Sometimes in a bathroom there are hinged mirrors on either side of the main mirror. These may be pivoted until they are at right angles to the main mirror. Or simply obtain 2 mirrors and butt them together at 90 degrees.
When you look at a mirror, your reflection is a 'mirror image of you.' When you look at the intersection of 2 mirrors that meet at 90 degrees, you will see -- at the intersection -- another image of yourself that is not a mirror image. It is you turned around so you are seeing your reflection the way others see you.
That virtual image of you always appears at double the distance from you to the mirror, and with the joint between the mirrors exactly between you and your virtual counterpart.
Now here is where things become (for one-eyed me) a bit weird. (I am assuming that you are doing this as you read, or at least imagining that we are both looking at the intersection of mirrors.) Since I am looking at the scene with my left (good) eye, the intersection seems to cover the left eye of my reflection. If I close my left eye and look at my reflection with my right eye, the intersection of the mirrors pops over to cover the right eye. This is exactly what you will see if you look at your image with only one eye.
When I ask someone like you (whom I am assuming has stereo vision) what you see when you look at your reflection with both eyes, your answer makes no logical sense to me.
You are likely to say, "The intersection appears to be half way between me and my reflection."
So I, trying to determine what that means, ask, "Is the line of the intersection passing through your left or right eye?"
"Ah, neither. It's half way between me and my image."
Now, we both know what each eye is seeing. For each eye, the line of intersection is blocking that eye.
"So, that means that neither eye is blocked...?" I prompt knowing that for each eye, one eye is blocked and the other is visible.
"No, neither eye is blocked. There is only one line and it is half way between me and my virtual image"
"So, if the line is not blocking either eye," I ask, experiencing some frustration, "does the line of intersection pass between your two eyes? Is it blocking your nose?" I am asking this knowing that for neither of your eyes is the line blocking the nose. I could understand if you saw two lines.
"Yes, maybe it is blocking my nose."
When I hear this latter comment I know that I don't fully understand your incredible stereo experience!
If you have read all of this and have any comments or questions, I would be delighted to hear from you. Write to Amblyopia Robert. Because of my work with exhibit design I have been able to experience stereo vision using active stereo goggles and other techniques. As a result of the art of my eye doctor, I have a reasonable balance between my two eyes as well as with the clarity and scale of the image produced with my right eye.