Monday, March 14, 2011

Thoughts on esotropia (and scotomas)

Sometimes, I lay awake at night, thinking of esotropia and how mysterious it is. I've read and heard over and over that exotropia is easier to treat than esotropia. Good thing I'm exotropic, I think to myself. But then I remember that I used to be very esotropic. I was a cross eyed baby! I had congenital/infantile esotropia. That's how this whole strabismus mess started.

I developed exotropia after my first surgery, and then a second and third surgery couldn't get rid of it. Is it really true that, because my strabismus surgeries accidentally made me exotropic, I now have a better prognosis than my esotrope friends? Even though my original condition was esotropia? That seems weird to me. Or lucky. Or something.

Perhaps it's all a mystery, and nobody knows...

After my previous post on suppression scotomas, I got interested in drawing out the suppression scotomas of esotropes. So here goes.

Both eyes are able to see the diamond, one centrally and one peripherally, and double vision should result because the eyes are not aligned. However, only one diamond is seen, because the peripheral diamond image is falling on a suppression scotoma.

In my previous post, I also mentioned that I had a habit of peeking around my suppression scotoma by overconverging. Is it possible for an esotrope to peek around their suppression scotoma? Yes!

If both eyes overdiverge and fixate on a point behind the diamond, that would make the diamond image fall outside of the suppression scotoma (and the image would double). However, this is easier said that done. I have trouble diverging my eyes at will, and I can imagine that an esotrope would have the same difficulty. After all, if they could diverge their eyes like that, they wouldn't be cross eyed! So it's possible that this may not happen as often.

It does explain something interesting, though. I am an exotrope, and I have trouble with physiological diplopia in front of the image I am fixating on. This is the kind of diplopia that happens when you put a pencil in front of your face, and make it double while looking at your professor. And when looking at the Brock string, I tend see an upright Y. I have trouble making the strings double in front of the bead. In both cases, the problem is the same: difficulty doubling in front.

My blogger friend Lynda, an esotrope, has the opposite problem. She has more trouble causing objects behind the image to double. While looking at a Brock string, she sees an upside down Y. She has trouble making the strings double behind the bead - difficulty doubling behind.

Both of our problems can be explained by looking at our suppression scotomas. As an exotrope, overconvergence causes images to fall outside of my suppression scotoma, and diplopia behind the fixation object is easier.

As an esotrope, Lynda would be the opposite. She probably has an easier time seeing diplopia by overdiverging, and thus seeing a double image in front of the object.

In conclusion, suppression scotomas explain everything in the world.


  1. Josh, the drawing is awesome, seeing my scotoma slide around to my nose!

    I don't diverge. Not yet anyway. Trying to diverge to 13". So over-diverging ain't gonna happen. One eye or the other constantly turns in when I see far.

    Instead, I think my scotoma is responsible for parts of the X forming and fading, on and off. By continuing to look soft until I can "hold" that image on, I am teaching my brain to switch off that scotoma, maybe?

    Also, my theory for seeing the inner strings is simply because my centration point (where I do have fusion) is very close to my nose. Is your's further out?

    Lastly, my "looking soft" is helped by looking just over the top of the bead. Then the X forms around the bead. I've been wondering if you would see the inner strings by trying to look soft slightly in front of the bead?

  2. Or ... maybe my last sentence is that "over" converging, diverging you are talking about! :-)

  3. Hahah I have to laugh for a second because this conversation is nearly incomprehensible to me, and I know what we're talking about. I can't imagine what someone else who tries to read this would think! This is super nerdy eyeball talk for sure.

    Anyway, I was guessing that divergence would be hard for you esotropes, since it's hard for me and I have one eye that is constantly diverged. It would be even harder if I had one eye that was stuck looking at my nose all the time.

    I still think that the position of the suppression scotoma on an esotrope probably DOES help with divergence / seeing the diplopia in front the object, and hinders seeing diplopia behind an object. The difficulty diverging in the first place is more of an eye muscle issue than a suppression issue. Even in that limited range that you can diverge, those strings behind the bead want to disappear because of the suppression scotoma. And then it sounds like you look past the bead (overdiverge) to get the X to appear. It's all scotomas!

    I'm not so sure where my centration point is, actually, or if I have one. I'm good at a range of near distances. It those distances that are out of arms reach that get difficult for me. But even though I can fixate on a near object, I still have trouble getting diplopia in front of an image because of where my suppression scotoma is.

  4. You two are really getting deep into this. I love this conversation. Josh, in terms of exotropia being easier to treat, you're exotropia is different than what you have been reading. Post-surgical strabismus is a much more complicated issue and that may make your treatment even more difficult because your brain started out compensating for esotropia then had to compensate for exotropia.
    As you know you likely never had trouble with an eye-muscle, it was your brain's inability to merge the images together. I'm sure your ophthalmologist didn't just keep missing 3 times in surgery, your brain just wasn't primed to accept both images so it did whatever it could to make it easier to suppress. If you only consider the muscular aspect of strabismus you are likely to fail (the big difference between ophthalmology and developmental optometry).
    In terms of suppression zones you are both right. Lynda has a centration point for her esotropia that is close to her nose. She is able maintain double strings in front not from seeing double, but by seeing physiologic diplopia and she is most likely not diverging enough. It is the beginning of processing information as a person with "normal" binocular vision. In your case your suppression zone is at near since you have adapted to your outward eye turn. You most probably have an all or none phenomena occurring. You can converge with effort but it's difficult to control (up to this point) in free space naturally. This is a very complex topic but I wanted to chime in while I had a few minutes. Best of luck to both of you, you are a true inspiration not only to other people with strabismus but the doctors treating them as well.

  5. Hi Dr. Press (suddenly there are two!),
    Thanks for your input on this. I had kind of been guessing that my surgeries had probably made things more complicated, rather than better. And I think you're right that my problem is not primarily a muscle problem. I actually have better voluntary control over my eye muscles than most of my normal eyed friends! (I know this because I like to experiment on them with my VT homework.)

    And thanks for your insights on suppression. For whatever reason, it's become my favorite subject to talk about. Feel free to continue to chime in!