The Eye (3)

The way that we think about designs and art is profoundly influenced by the anatomy of the eye. By understanding how the eye works, we have the building blocks for learning about how our eyes interface with our brain to create feelings, thoughts, trigger memories, and inspire actions.

In this post, we will walk through the essential components of the eye. Of course, there is certainly more to the eye than can be covered in this post, but we will focus on the elements that will inform our discussions in future posts.

Below is a diagram of the parts of the eye that we will cover.

As an overview, the light passes through the cornea then the pupil, and goes all the way to the back of the eye. The light goes through the eye and doesn’t get processed until it hits the back of the retina.

The cornea is the primary lens of the eye, protects the eye, and serves to focus around 80% of the light that comes in. It is a fixed shape and it is a living tissue, so it can be damaged.

The pupil is an opening in the eye that allows light to come in. Think of an aperture in a camera. Depth of field relates to pupil size, or the distance that objects may appear in focus. Depth of field is inversely related to pupil size: Large pupil = small depth of field. The lenses of the eye bend light to allow focusing based on distance.

 

If you are in dim light, the pupil will expand to let light in. When it is all the way open, the pupil allows 20 times more light in than when it is small. As an aside, pupils have a bunch of really interesting other functions, including showing arousal. Research has found that people with greater pupil dilation are rated as more attractive.  

The fovea looks like an indentation in the retina and is the location where the center of what you are looking at projects onto the retina. For example, if you are looking at the letter B the part that you are focusing on (at that very second) will hit the fovea. Images that don’t land on the fovea are actually blurry, but your brain combines information as you look around to create the illusion of clear vision. I’ll describe more about how this works in future posts. The fovea is very small and corresponds to 1-2 degrees of visual angle.

What is visual angle? you may ask…

When a large object is far away (like the Eiffel tower in the above photo) it appears to be small, but small objects that are close appear to be large. This is due to the size of the object that makes it to your eyes, which is based on the physical size of the object and the distance from you. We can use the term visual angle to describe the relative size of objects that you see. Looking at the image below, both the man and the Eiffel tower have the same visual angle of around 12 degrees, because of their relative size and distance from the eye. 

You can approximate the visual angle using the methods described in the figure drawing video below. If you hold out your thumb at arm’s length, your thumb width is about 1-2 degrees of visual angle.

Next, the retina is one of the most important parts of the eye. It is a complex layer of cells made out of the same tissue as the brain. The Retina is much like the brain of the eye. It contains photoreceptors which collect information from the world and transmits this information to the brain.

 

The optic disk or blind spot, is the region where the optic nerve fibers leave the retina. There are no receptors there and you can not see objects that are projected onto your blind spot.  Here is a video that will help you find your blind spot.

You may not feel like you have a blind spot. Why do you think we are not aware of it? We constantly look around and fill in the information missing from the blind spot,  so we don’t even notice it.

Finally, the optic nerve is a bundle of nerves that sends information from the retina to the brain and gives information from the brain to the eyes.

 

Below are a few terms that you don’t need to know but are interesting if you are that kind of person.

*Aqueous Humor, provides nutrition to the cornea and lens. It also functions as cushioning and carries away waste. It is constantly recycling. About every 4 hours it fully replaces the fluids.

*Vitreous humor: the liquid in the eye,  also provides nutrition. It does not reproduce and accumulates gunk or floaters, which increase over time with age. You can see them when you look at a white paper or at bright light. Why is that? It is because white objects bounce the most amount of light and what you see as floaters are shadows cast by the intense light. Neat right!?

*The iris is what you associate with your eye color, but it is a muscle that controls the pupil. The outer layer contains the color pigment in the blood vessels.

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