Seeking Stereopsis

Glad you like my blog! I've heard from lots of people who have strabismus or a related condition. It seems fairly common, but people aren't aware how common it is! I had no idea what was wrong with my eyes, because my strabismus is subtle enough that it usually wasn't obvious that my eyes weren't pointing at the same thing. So it took me a long time to figure out what was going on and find somewhere that would spend the time to treat me and help me fix the problem. I've definitely made leaps and bounds since then, though!

From what I know about the surgery side of things, it's like you said. It fixes things cosmetically, but your eyes still need to be trained to work together.

For people with misaligned or damaged eyes, depth perception is limited. Monocular depth clues like shadows, comparative size, and motion parallax do exist, but binocular vision allows for a more accurate perception of depth. Researchers at Japan's University of Yamanashi are working with off-the-shelf augmented reality glasses to offer improved depth perception for the binocularly challenged.

Sorry for the lack of updates! As I said, I've stopped active vision therapy and now I'm just doing maintenance. Here's how I feel about the final results:

Overall, I'm not sure that my vision has really improved much. There's certainly a difference in my vision, but how that affects my quality of life is not obvious.

I now use both eyes much more than I used to. That's great, but I don't really notice a difference. I didn't have the world suddenly "pop" into 3D, like others who have done vision therapy. I guess it's possible that I have subtly more information about the world and I'm not aware of it. Maybe I'd be better at doing tasks that require depth perception now than I was before. I can certainly do things like watch 3D movies, now.

On the negative side, however, I now have a little bit of double vision. When I started therapy, I didn't have double vision. My main problem was that I frequently wanted to close one eye when trying to read things that were far away. This doesn't happen anymore, but I think my prism glasses fixed that, rather than the therapy.

When I have double vision, I'll see two of whatever I'm looking at for a split second, and then I try to adjust my eyes so I only see one. Much of the time I can get it back to one image, but then I often lose it again. This happens more frequently when I'm tired, but also when I'm not. Sometimes, if I'm really tired, the only solution is to stop doing what I'm doing. So I'm not very happy with that.

I spoke with my doctor about this, and she says it's fine, as long as I can quickly get it back to one image. Maybe it's fine, but it's sure annoying!

I'm not sure where to go with this from now on. I am still doing eye exercises a few times a week, mainly the Brock string. I can actually tell that my eyes are still improving at that task. So I feel like there's hope that I will eventually get the double vision under control.

Although my doctor says I won't benefit from more vision therapy, I still think that with more work I might be able to improve the double vision a little more. We spent a lot of time working on me using both my eyes, and very little working on pointing them in the appropriate direction.

A longer update is coming, but I just wanted to share that I went and saw Jurassic Park 3D the other week and I could see the 3D! I was excited to be able to see it, but I actually found the effect somewhat distracting. And it made my eyes very tired.

This is a big change for me! I watched all of Avatar wondering why people were so impressed with the 3D, when everything looked normal to me. Then for one split second I saw it, and realized that I was missing something that everyone else was seeing. During Hugo 3D, the only part that looked remotely 3D was the snowflakes falling in the beginning. But during Jurassic Park I saw 3D the whole time, consistently!

On a related note, here's an article about a guy who discovered he could see in 3D using a Nintendo 3DS gaming system, but not in real life. I'm still not sure how much 3D vision I'm getting in my daily life, but it certainly has improved from what it was! What this guy is describing sounds much like the state that my eyes were in prior to vision therapy.

Turns out Hillary Clinton has glasses with a prism -- just like mine!

Those tiny vertical lines you see on her glasses are from a fresnel lens, which is a type of prism that is often used as a temporary stick-on addition to a normal pair of glasses. This probably means that Clinton was experiencing some double vision as a result of some medical issues.

Last week I had a second eye exam, identical to the one I was given when starting vision therapy. My optometrist wanted some indication of how much progress I've made since then. After we went through all the tests, she said that I was suppressing the images from one eye much less often, and that, although I still had an eye turn, it was intermittent, instead of constant.

I didn't notice much difference in most of the tests (to my disappointment, I was still unable to see any of the 3D images they use to test stereo vision ability). But there was one test that really stood out. It's called the Worth 4 Dot test. When I was first starting vision therapy, they gave me this test on about 4 different occasions, and I hated it. Every time they brought out the red/green glasses, and the little flashlight-wand that is pictured above, I felt a little pit of dread form in my stomach.

When wearing the red/green glasses and looking at the wand, what you should see, if you have normal vision and are using both eyes at once, is exactly what you see in the picture - 4 dots. But what you see if you suppress one eye or the other is only two or three, depending on which eye you suppress, because one eye can see the 2 green dots and the 1 white dot, and the other eye can see the 1 red dot and the white dot.

It gets more complicated if, like me, you are intermittently suppressing an eye and alternating between left and right eyes. In that case, you will see things shifting back and forth rapidly from three dots, to two dots, and back again, with nothing constant for more than a second or two. For brief moments you might see three dots in the middle of the room and two dots over on the other side of the room, separated by a large distance. It's a confusing thing to see, much less describe to an optometrist who just wants a simple answer to the question "how many dots do you see?" There was no answer to that question! At any moment I might see anywhere between two and five dots in various locations (or maybe zero if I got frustrated enough to close my eyes). I think that was what so annoyed me about the test. It was so confusing to my brain that having to attempt to put it into words just made me really, really cranky.

Vision therapy update:

I haven't been posting much because I haven't made very exciting progress recently. I am definitely still improving. I am slowly getting better at using the Brock String, and making my eyes point at the same thing, and not suppressing the input from one eye. I am still getting some double vision, particularly when I'm tired or when I'm not wearing my glasses.

It seems that whenever I try a new exercise, I make leaps and bounds right away, but getting all the way to the point where my eyes behave like a normal person's would is slow and difficult. I'm trying to remain motivated but it's a bit of a challenge. It's nice when there's really obvious daily progress, which hasn't necessarily been the case. These things take time.

Last weekend I started noticing some double vision for the first time. This is an expected result of my vision therapy, and although double vision is normally a bad thing, this is actually a good sign.

The reason is that the first step to getting my eyes aligned is to break the suppression that my brain is currently placing on one eye at a time. Once I'm successfully using both eyes, it will be possible to work on pointing them in the same direction. But since my eyes don't point at the same thing yet, when I use both of them I end up with some double vision. So double vision is a good sign because it means that I'm using both eyes at once.

So far the double vision hasn't been causing me any discomfort because it has only been for brief moments, and most of the time it only happens when I've been trying to make it happen. It really just looks like there are two of whatever I'm looking at. Last night in the dark I went to look at the LED clock on the microwave and it looked like there were two of them, side by side, for a brief instant.

Vision Therapy Update -- The Brock String

Here's a little update on my vision therapy progress. I've been doing vision therapy for 4 weeks now. So far I haven't noticed any changes in my daily vision, but I am getting better at the exercises I've been working on.

Currently we are mostly working keeping me from suppressing the input from one eye. This involves a lot of activities wearing glasses with one red lens and one green lens, and looking at red and green things. I have an eye chart with letters which are half red and half green, so that if I look out of only one eye, half the letters disappear. That was hard at first, but now it's too easy. So my optometrist is now setting me up with different strengths of prisms. When I place a prism in front of my eye and try to keep all the letters visible, it's much more difficult, because I have to work much harder to get both my eyes pointing in the right direction, and keep my eyes from suppressing as a result.

Beauty in the right eye of the beholder – finch chooses better mates with its right eye

From Not Exactly Rocket Science:

It’s said that beauty is in the eye of the beholder, but that’s only half-true for the Gouldian finch. Jennifer Templeton from Knox College, Illinois has found that these beautiful birds only display their famous fussiness over mates if they’re looking with their right eye. If the right is shut, and the left eye is open, the birds have more catholic tastes. As Templeton writes, “Beauty, therefore, is in the right eye of the beholder for these songbirds.”

My glasses

My glasses are unusual because of my strabismus. To correct for the fact that my eyes point in slightly different directions, my glasses have a prism ground into them. Prisms, rather than just focusing the light so that things aren't blurry, bend the light so it is in a different place. This makes the two images that my misaligned eyes see look closer together. This helps a lot with the symptoms of my strabismus. The main symptom I had was the desire to close one eye when reading something far away. That's now mostly gone. However, due to the glasses, another issue popped up. When I first put the glasses on I noticed a lot of chromatic aberration. Chromatic aberration is the phenomenon where different wavelengths (i.e. colors) of light are bent different amounts by the prism. If blue is bent significantly more than red, those colors will separate, and you'll get a spectrum. This is why you see a rainbow when you shine light through a triangular prism like the one above. The amount chromatic aberration produced depends on a property of the material called dispersion. In glasses this property is supposed to be minimized, but there will always be some amount of dispersion. To get less dispersion you usually have to go to a more expensive material.