Watch a 3D Show: How Do Our Eyes See in 3D

Seeing in 3D

One of the most important capabilities of our eyes is to see in three dimensions or 3D. In order for us to see in 3D we must first have two good eyes located on the front of our head. This allows us to see the same object at two slightly different views that our brain then merges into one, so we don’t see double. You can easily try it by looking at an object and taking turns covering each one. The light reflected off of the objects you see enters each eye separately; it is converged by your lens on the back of the retina and sent to the brain. Our brain is then able to match up the similarities and fill in the subtle details, and differences captured by each eye. We are then able to see a solid object in 3 spatial dimensions width, height, and depth.

Adapting

As we view the world around us our eyes are constantly adapting to our environment around us. In order for us to see, several parts of the eye must refract light so that it produces a clear image on our retina. As light enters our eyes the cornea first bends it towards the lens. Our cornea has a distinct bulging shape that causes light to refract similar to a double convex lens. The focal length of the cornea lens adapts with the contraction or relaxation of the ciliary’s muscles changing the lens shape. After the cornea has refracted the light entering the eye, what we see is a real image formed by the actual convergence of light rays at a point in space.

Refraction

Our eye’s ability to refract the light that enters at the right focal length is what allows us to see clearly. Since the eye rotates in its socket it is able to accommodate the light that enters onto the more sensitive areas of the retina with ease. The distance from the cornea to the retina is a fixed and cannot be altered. Ciliary muscles attached around the edge of the lens contract (stretch) or relax to change the convex shape of the lens. So, for viewing objects that are near, our lens needs to have a short focal length and be contracted. For objects that are distant, the ciliary muscles relax to lengthen the lens’s focal length allow it to stretch out. As we grow older ciliary muscles wear and it becomes increasingly more difficult for use to focus.

Powerful Ideas!

• The refraction of light off of objects is what allows us to see them.
• Lenses refract or bend light differently depending on their thickness.
• Lenses that are different shapes and sizes can work together to produce clear images.
• Light always travels in straight lines.
• Lenses can converge or diverge light depending on their shape.
• Our eyes are made up of a lens system that converges light on our retinas so we see a clear image.

There are several ways to see the pictures hidden in the Magic Eye images. The preferred method is called parallel viewing. Normally your eyes want their focal point to be on what is in front of you, like this piece of paper. In order for parallel viewing to take place you have to get your eyes to focus behind what is in front of you. It is sometimes easier said than done, but with practice makes more sense. The idea is to get the ciliary muscles that are around your lens to relax and lengthen out. You will know when they relax because everything will go fuzzy. Once this happens we can start to see in stereovision. Light refracted from the image enters our cornea and is bent to our lens that is currently stretched out. Our two retinas send the different images to our brain where the two images are merged and the brain decodes the differences allowing the 3D image to come forward. Sometimes it can take a few seconds for the brain to decode the differences so be patient.