Monday, February 14, 2011

Abnormal retinal correspondence

NOTE: I wrote this post when I didn't know very much about ARC. For a better post with better information about ARC, please read this updated post.

Abnormal retinal correspondence (or anomalous retinal correspondence) - ARC - is something that I worry about like a hypochondriac. I'm periodically convinced that I have it and that I'll never be able to achieve stereoscopic binocular vision. So, I thought it was time to write my worries down on the internet.

First of all, what the heck is it? Well... I'm not exactly sure. That's why it's so scary! It's a nebulous dark monster, waiting under my bed for it's chance to eat me. I've read a million things about it, and I feel like I get a different answer every time I read about it. But I will try to explain MY understanding of it, which could be completely wrong.

The first time I heard of ARC was in Fixing My Gaze, by Stereo Sue, quoted below:


When we suppress input from one eye, we lose up to half of the visual information that's available to us. So, some people with strabismus unconsciously develop an additional strategy that allows them to make simultaneous use of both eyes, even though the eyes are looking at different regions of space. To do this, their brain abandons the idea that the two foveas point to the same location in space. Instead, they aim one eye at a target and interpret the location of images that fall on the central retina of that eye as straight ahead. (Assume here that the head is turned neither right nor left but is oriented straight forward.) Though aware of images that fall on the fovea of the strabismic, or turned, eye, they localize these images with reference to the "straight ahead" direction. If, for example, the strabismic eye is turned by 10 degrees, then images formed on the fovea of that eye are interpreted as being located 10 degrees from straight ahead. The fovea of the straight eye no longer corresponds with the fovea of the turned eye but instead with an area of the turned retina shifted by 10 degrees.

This is how my friend Bruce Alvarez sees... His response to the hole-in-the-hand experiment is different from what you probably observed if you tried it. He sees the hand in half of his visual field and the tube of paper in the other half. Bruce does not merge the input from the two eyes but instead reports what each eye sees separately. Although this is not the response that most people have, his view of the world, in this case, is actually the more accurate one. After all, the tube of paper is to one side of the free hand. Indeed, it is surprising to him that someone would have a different response. Bruce's unusual way of seeing is called anomalous retinal correspondence, an adaptation that often takes months or years of childhood strabismus to develop...


The hole-in-the-hand experiment that she is talking about is this: Hold your hand up to one eye. Hold a cardboard tube up to the other eye. If you have normal vision, you will fuse the images and it will appear that your hand has a hole in it. If you are completely suppressing, you will just see a cardboard tube OR your hand. If, like Bruce, you have ARC, you will see reality: a hand next to a cardboard tube.

When I read that passage, I thought to myself, "When I do the hole-in-the hand experiment, I see what Bruce sees.... And I feel like I still see a lot out of my deviated eye... Hmm... interesting. I must have that ARC business."

Before I discuss myself further, though, let me try to explain my understanding of ARC. Again, I could be misinformed, but this is how I have come to understand it.

On the retina of each eye is an area called the fovea. It provides you with your clear, sharp central vision. In your brain, there is a LINK between these two foveas, and your brain operates under the assumption that the two foveas are ALWAYS pointing at the same place in space. In other words, the two foveas CORRESPOND to each other, and the brain fuses the image from each fovea into one stereoscopic image. Why does it fuse them together? Because, it is operating under the assumption that the two foveas always point to the same place in space.

This all works great when the two eyes are ACTUALLY pointing at the same thing, as in the image above. But what happens when one eye is strabismic and pointed at something else? Visual confusion or double vision results. Why? Because the brain still believes that the two eyes point at the same place in space. Thus, it fuses the images together into a crazy mess.

Going through life with double vision and visual confusion is not very easy, though. So the brain usually adapts by suppressing the image from one eye, trying to create some semblance of normal vision. The retinal link still remains intact.

There's a weirder, sneaker way that the brain can adapt, however. Break the retinal link! If the brain stops assuming that both eyes point at the same area of space, then the problem is solved. It adapts to the sad truth of reality: both eyes are NOT pointing at the same thing. Thus, each eye acts as an independent camera, with the images from both eyes being neatly pasted together in the middle.

This is ARC. The brain gives up on the notion that both eyes point at the same place in space. Instead of suppressing half of the visual field, it joins them together in the middle to create a panoramic view.

(I've read that ARC is much more common in esotropes, but I'm not sure how it works. Do they see a panorama? I'm not sure what they do...)

Anyway, back to myself. After reading that passage of Stereo Sue's book, I said "Okay, I have must have ARC. What an interesting factoid," and I didn't really think much of it. It wasn't until later, after researching it more, that I realized that it was not a good nor interesting thing. I read in Dr. Greenwald's book that Dr. Brock believed that ARC was incurable (though Dr. Greenwald himself did not believe this and had developed his own system for treating it). I also read that trying to convert ARC to NRC (normal retinal correspondence) can sometimes result in permanent double vision, and that some eye care professionals won't attempt it. And various other places, I just simply read that it was very hard to treat, with phrases like "exceedingly difficult" and "poor prognosis" being used.

At this point, I asked my optometrist and vision therapist if they thought I had ARC. Both of them didn't think that I did, and said that it was rare. My optometrist didn't think that I had it, but didn't really have the tools at the time to check if I had it or not.

So I said to myself, "I'll just figure it out myself." Here are my findings:

Josh's Findings
A report.

Hole in hand activity:
Result: Fail.

Camera flash test:
This classic ARC test involves flashing each eye with specially taped up camera flash.

-Hold it horizontally in front of one eye, stare at the piece of black tape in the middle. Flash.
-Hold it vertically in front of the other eye, stare at the piece of black tape in the middle. Flash.
-Close your eyes. Open your eyes. Look at a blank wall. Describe what you see.

When I do this test, I usually see one of the ARC versions. BUT, if I blink my eyes a lot, the two lines start moving toward each other into the NRC formation. What does that mean?!?! Fail? Pass?

Color Luster:
Wear red/green glass. Look at a light box. Try to mix the colors together. You fail if you see a half red light box, half green light box. My result: Mixed. I can see half red half green all day, but I can also make them mix a little if I squint and blink a lot.

Lid Glow:
Close one eye. Shine a penlight in your closed eye. Look at a black dot on the wall with your open eye. Try to make the black dot on the wall move into the glow you are receiving from your closed lid. Result: Pass... kind of. It's hard to do, but I can make it happen if I turn my head and blink a lot.

String test:
Wear red/green glasses. Hold a Brock string up to your nose. Fixate on a bead and make an X. If the GREEN string comes out of the RED eye, and the RED string comes out of the GREEN eye, you pass (crossed diplopia). Result: Passed with flying colors!

Bagolini Striated Lens test:
I won't go into detail about this test, but I got a weird result. I didn't get the ARC result, but I got uncrossed diplopia when I was supposed to have crossed diplopia (I think...). Result: Mystery.

Evidence for ARC:
I do a lot of things that one with ARC would do. When put on red/green glasses, relax my eyes, and look around the room, I see a half red half green room. I also feel that when doing fusion activities, I have to overcome the initial tendency to "paste" images from each eye together side by side. The first time I looked into the cheiroscope, I saw two totally separate images with no fusion. The same thing happened the first time I looked through a stereoscope, and the same thing happened when I first tried to do mirror overlap. Side by side images pasted together; panorama. I have also found it hard to gain even peripheral stereopsis, which is supposed to be "easy" (but this just changed today, see below).

Evidence against ARC:
I can also do a lot of things that one with ARC shouldn't be able to do. For example, I can make my eyes work as a team and play cards with antisuppression playing cards. I can see and play around with red/green tranaglyph slides. I can flat fuse a polarized vectogram into one image. I can do flat fusion stereoscope activities. And just today, I finally saw some depth on a polarized vectorgram! (but that's for another blog post).

I believe have some ARC, but I am able to switch to NRC when doing vision therapy exercises that provide me with enough feedback (such as with anaglyphic activities and the Brock string).

I also believe that I have been self treating this ARC instinctively. When doing red/green anaglyphic activities, I often place objects that can only be seen by the RIGHT eye on the LEFT side, and objects seen by the LEFT eye on the RIGHT side. I then proceed to touch all over them with my hands to keep them "on." I have done this because it is "harder", and I now realize that it forces me to fuse the whole visual area into one image, and reinforces it with motor feedback.

If the object that can only be seen by the RIGHT eye is placed on the RIGHT, and the object that can only be seen by the LEFT eye is placed on the LEFT, then it is possible for me to "paste" the images together, even when wearing red/green glasses. Thus, the activity can be rendered useless by a smart brain if you're not careful.

I certainly hope that my tendency for pasting images together in ARC fashion isn't an insurmountable obstacle for gaining binocular stereoscopic vision. I work very hard to do my vision therapy homework and to force my eyes to work as a team. And I am usually successful. But I still have that lingering fear... What if it never happens? What if my brain is just broken?


  1. Thanks for the encouragement!

  2. I'm rereading yours and Sally's posts, trying to find terminology for my own on my recent therapy. This just jumped out at me:

    I read in Dr. Greenwald's book that Dr. Brock believed that ARC was incurable (though Dr. Greenwald himself did not believe this and had developed his own system for treating it). I also read that trying to convert ARC to NRC (normal retinal correspondence) can sometimes result in permanent double vision, and that some eye care professionals won't attempt it. And various other places, I just simply read that it was very hard to treat, with phrases like "exceedingly difficult" and "poor prognosis" being used.

    I am fairly certain, by my therapist's initial concern about starting therapy, that I have ARC big time. Will keep ya posted.

  3. HI Lynda,
    First, I want to say that I shouldn't have said that Dr. Brock said it was incurable. What I read was more like, Dr. Brock thought that if you were cured of it, then on the deepest level, you didn't truly have it in the first place. Or something complicated like that. People HAVE fixed it, though. So I hope I didn't scare you (like I have been scaring myself). =)

    But anyway, that's an interesting point. Maybe that's why your vision therapist was reluctant, and said that you were too well adapted. I would definitely ask. I'd rather have all of the information, even if it's complicated. Knowledge is power!

    Do you remember a test where you put on glasses with diagonal scratches or striations in them? And then looked at a light? If you do remember that test, do you remember what you saw? An X? Or a V? Or...?

  4. I have the same response to the hole in the hand and the flashing experiment that you have, but I have some stereopsis now and am working on reducing central supression.  You can't expect to trick your brain into making impossible pictures at this stage.  I never had further surgery until last year because I was threatened with double vision, now I have peripheral fusion and depth perception, though my vision is certainly not normal.  And am getting better with VT.

  5. what the heck.... i have been living with ARC for 25 years (i m 27 btw) and i thought that's the normal vision when my vision suddenly become double and i experience NRC... i have been glad with my vision of ARC and thats how i thought everyone see... when i start havign this NRC (when i focus on an object the things in front and behind the object become double) i tot my eyes has screwed up and i went to many doctors and eye specialists only to be disappointed... many tot i have a normal vision now! i was still 'wtf' and never happy with this kind of vision.. and i am still praying that my vision will be restored to ARC the normal 1.