Did you know that like most standard eye tests, the Snellen test does not check one’s depth perception? Read on to learn more about the tests that specifically check your depth perception.
When it comes to seeing the world in three dimensions (3D), depth perception plays a crucial role. Without it, there’s no way we can recognize distances between people and/or objects in all directions. Many experts explain that animals are able to sense the distance of objects (depth sensation) within their environments. However, the term perception is reserved for humans, since we are able to tell each other about the experiences of distance.
By definition, depth is looking into a hole or tube and estimating forward distances. To do this accurately, one must have binocular stereoscopic vision, or stereopsis. If someone lacks stereopsis, perceiving depth may be more difficult and less accurate, and they must rely on visual cues other than stereopsis.
Our eyes use three methods to determine distance:
The size a known object has on your retina – Knowing the size of an object due to previous experience helps our brains calculate the distance based on the size of the object on the retina.
Moving parallax – A great example of this is standing face to face with someone and moving your head side to side. The person in front of you moves quickly across your retina, but the objects that are further away don’t move very much at all. This helps your brain calculate how far or close something is from you.
Stereo vision – Since our eyes are about two inches apart, each eye receives a different image of an object on its retina, especially when an object is close up. When the object is far away, this method doesn’t work as well since objects appear more identical when further away from your eyes.