Depth perception

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I had myself checked in today, as my glasses needed adjustment.

After the test where done I was informed that I didn’t have depth perception, and that he only got such customers 1 / 2 times a month.

We did a test in which the left eye had a +, and the right eye had a ( ).

If my eyes worked fine, then it should look like ( + ), but this isn’t the case. I’m not able to overlap both my eyes to get that, instead I only see part of it. Either a + from the left, or a ( ) from the right.

He informed me that this is called “Alternative looking”, but I’m not able to find anything about this online.

In: Biology

To have depth perception your brain needs to deduct depth from tiny differences between what is seen by left and right eye. Alternative looking sound like your brain is deciding to use either left or either right eye, not to combine those. It works similar in case of lazy eye, if not treated brain will just use only one eye, and view from the second one is just ignored.

In the simplest way that I can explain it, you need to have at least two eyes that are both looking at the same object from different angles for your brain to be able to determine how far away they are.

It’s sort of like the difference between watching a regular movie versus a 3D movie. In a regular movie, the images are in 2D because there’s only one camera. In a 3D movie, there are a bunch of cameras looking from different angles, and because of this, we can triangulate how far away objects are supposed to be.