Random Dot Stereograms

Disorders of binocular vision. They’re just the worst, aren’t they?! Convergence insufficiency, convergence excess (or their divergence counterparts), amblyopia, strabismus (esotropia and exotropia), esophoria and exophoria, hypertropia, etc. Where would vision therapy be without them, though? Many of our patients who suffer these types of disorders don’t even realize that anything is missing from their vision. Many of them have adapted since birth, so for them, something like double vision may just be their “normal.” Same with the total suppression of vision in one eye; these poor folks have no idea what it’s like for the rest of us to truly experience three-dimensional reality! Others, who have had the benefit of a lifetime of healthy and functioning binocular vision, may suddenly find themselves struggling to navigate the world with the onset of one of these conditions later in life.

Imagine being someone who develops diplopia, either from age or injury, trying to drive or watch TV. Just doing these regular everyday tasks without the necessary skills or awareness can be exhausting. You’re trying to wrestle your double vision back to single, when the very muscles needed to do so have atrophied. You must then make constant judgments about which of the two worlds you see in front of you is the “real” one. Eventually, it’s just easier to close or cover an eye. Do this long enough, and your brain will adapt, suppressing the vision from that eye entirely. Now you’re confronted with severe limitations to the depth perception that has guided you through the world since birth. How frustrating it must be to be constantly bumping into things, or knocking things over as you reach out to pick them up. Luckily, vision therapy clinics around the world are there to help. With the right tools and techniques, vision therapy can work those deficient skills back to full strength.

One such tool is the stereoscope. The first stereogram dates back to the 1840s, where two photographs are positioned side-by-side, and presented to the viewer. The trick is to present one image only to the right eye, and the other only to the left eye, usually by positioning some kind of partition between the two. The brain then takes over, and “fuses” the two flat images into a single 3-D image.

Most of us are familiar with rudimentary three dimensional images that require the use of “3-D glasses.” The first successful demonstration of this technique was in the 1850s when Wilhelm Rollmann used red and blue glasses to view yellow and blue images, however his technique only worked with line drawings. It wasn’t until 1891 that the first printed anaglyph was created by Louis Ducos du Hauron. This involved taking a photographic plate, and printing two negatives (which formed a stereoscopic photo) onto the same sheet of paper. One of the negatives was printed in blue or green while the other negative was printed in red. The viewer would then don a pair of colored glasses to view the printed image. A red filter was used for the left eye and blue (or green) was used for the right eye. When the image was viewed with both eyes, the brain would fuse the two images, resulting in an apparently three dimensional image on a flat sheet of paper! The novelty of this quickly took off, and was applied to all manner of images, and even motion pictures.

In vision therapy, we have all become familiar with Randot™️ or random dot images. These are often used in-office, where the patient looks at an image on specially filtered film while wearing reverse polarized glasses to find a three-dimensional image amidst a scramble of random dots. Computer programs like NeuroVisual Trainer, without the benefit of polarized monitors (or projection, as in modern 3-D movies), use anaglyph glasses, but the basic underlying principle is the same. It works something like this:

1. First, you start with an image filled with random pixelated dots, and duplicate it.

2. Next, select a region in one image. In this example, note the faint gray square in the center of the image on the right.

3. If you shift the selected region horizontally by just one or two dot diameters, and fill in the empty region with new random dots, you have a stereogram, with one image for the right eye, and the other for the left.

4. Now see if you can converge your eyes whilst looking at the Random Dot images above until you see three of them instead of two. If you can focus on the center area of the “middle” one, you should see that the selected region appears as a small, slightly recessed circle, sunken into the rest of the image. Congratulations! You have achieved stereopsis!

If you can't do it, don’t worry. It’s a tricky technique to fuse two stereoscopic images without the aid of a stereoscope or some other piece of equipment, like anaglyph glasses. Certain colors can be “canceled” by lenses of opposing colors from the opposite end of the visible light spectrum; red lenses cancel blue and green, so looking through a red lens makes anything blue or green appear black to the viewer. Conversely, blue and green cancel red to the same effect; anything red will appear black when viewed through a blue or green lens.

If you were to turn one of the Random Dot images red, and the other green or blue, then put on the appropriate anaglyph glasses, the mutual cancellation of the colors in the images by the opposing colored lenses in your glasses would help your eyes and brain to work together in achieving binocular fusion, and hopefully stereopsis, too! This is primarily how NeuroVisual Trainer’s suite of Random Dot Exercises work. The next step toward therapeutic efficacy is to gear those images to get the eyes and visual system to do what you want them to do.

As demonstrated in the sample images above, you can create an area of apparent positive or negative depth in the image by aligning the scrambled dots in certain ways. By assigning a certain color to one eye or the other, we can simulate Base Out or Base In prism to create convergence or divergence exercises, or even Base Up or Base Down for vertical vergences. You can also alternate between them to force the patient to “jump” from converging & diverging in a Jump Duction exercise.

Put on your red/blue glasses. Are you bugging in, or bugging out?

Because binocular vision disorders are so commonly treated by vision therapy, the Random Dot family of exercises are probably among the most often used activities in the NeuroVisual Trainer toolbox. The patient is presented with a large outer shape (circles are the default), and a smaller inner shape that appears to be popping in or out. The inner shape will appear in either the top, bottom, right or left quadrant of the outer shape, and the patient simply hits the arrow key that corresponds to where they see it (or on a touchscreen, they swipe with their finger in that direction).

Like all of our interactive exercises, there are a host of customizable parameters that can be configured to tailor the experience to an individual patient’s needs:

• Adjust the duration of the exercise.
• Change the amount of prism separation the exercises will change with each step.
• Set a custom working distance; for example, you can work distance vergences by increasing the working distance for a given instance of a vergence exercise, without affecting the overall calibration settings on a patient’s device.
• Change the shape (circle or square) of both the inner and outer shapes, as well as their overall size.
• Change the amount of apparent depth of the inner shape to increase or decrease the binocular demand, and whether it “pops” in or out (or you can randomize it!)
• Adjust how long the exercise will wait for a patient to make a selection before it times-out and moves on.
• Don’t forget that you can also create Grid Schedules in NVT that include multiple configurations of a given exercise to build progression over time. NVT gives you the tools and flexibility to use as best suits your approach and your patients needs.

Now put on those cool glasses and get to work!