What are the Major Parts of the Eye?

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  • Written By: Mary McMahon
  • Edited By: Bronwyn Harris
  • Last Modified Date: 12 August 2018
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The eye is an amazing animal organ that is capable of converting waves of light into signals that the brain understands, in turn conveying an image to a person. It is also an extremely complex organ. Learning the basic parts of the eye can help people understand conversations with an ophthalmologist, or eye doctor, and will also assist with illustrating how the the organ works.

Working from the outside in, at the surface of the eye is the cornea. The cornea is a transparent, soft layer that covers the delicate and complex layers underneath. Damage to the cornea will impair a person's vision, but it is also one of the fastest healing parts of the body. Underneath the cornea is the sclera, or white of the eye, along with the iris and pupil. The iris is the colored portion, while the pupil is the dark area in the middle of the iris. The pupil expands and contracts to admit light to the back of the eye.


Behind the iris and pupil is the lens. The lens focuses light, directing it through the vitreous humor to the retina. The vitreous humor is a viscous fluid that fills the space between the front and back of the eye, protecting the delicate optic nerve and retina in the back and helping the eye to retain its shape. The retina is the light sensitive area in the back of the eye that is equipped with several structures that help translate the light focused through the lens into an image.

The two commonly known receptors in the retina are the rods and cones. Rods are extremely sensitive to motion and are concentrated along the edges of the retina. The rods are responsible for night vision, as they are more sensitive to subtle changes in light that can translate into shapes and peripheral movement. Cones account for the ability to see in color, and they are closely concentrated in the middle of the retina, the area called the fovea. The fovea is located at the center of the field of vision, and it is covered by the macula.

The numerous photo receptors of the eye are connected to an assortment of nerves and blood vessels which all ultimately connect to the optic nerve. This vital part connects with the brain, sending a series of electrical signals that the brain interprets as an image. Because of the way in which light is filtered through the eye, images of what a person sees actually arrive upside down, and the optic nerve flips them right side up so that the viewer can correctly understand what is going on.


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Post 10

@Mor - Yeah, I did a bit of research on it because I've been thinking about getting my short sightedness corrected. Apparently most of the surgery is done with lasers and is very quick and easy.

It's the after care where people often make mistakes. You have to be very careful to follow instructions to keep the area disinfected, because an eye infection on recent surgery can lead to blindness if you aren't careful.

I don't believe even that happens very often at all. But, at the moment it's mostly laser eye surgery cost that's stopping me from doing it. Once the price comes down it will be a different story.

Post 9

@ddljohn - That kind of surgery on an eye problem is very common. They do it in order to fix myopia all the time now. From what I've heard the cornea heals itself in basically a few days.

It's scary, because often you'll be awake for it, even if they numb and immobilize your eye. And these fears are definitely something to talk to your doctor about, because really, any surgery has some risks. But, for a surgery, it's pretty safe.

Post 8

@donasmrs - Something that scientists have found really fascinating is that animals like octopuses and squids actually evolved and developed eyes separately from animals with spines. Even though they are very similar, the octopus eye is also different, for example in that it doesn't have the blind spot caused by the optical nerve that most animals have.

With that said, all eyes, whether they be insect, human or cephalopod, have a common ancestry and probably developed from photo sensitive cells. Having the ability to see would have been such an advantage that it must have developed quite rapidly once they got past the initial steps.

Post 7

@donasmrs-- That depends on which animal we're talking about but many animals have very similar eye structures as humans.

I don't know if eyelids are considered part of the eye but I know for example that cats have a second eyelid that they use to coat and protect their eyes in certain situations. It's visible sometimes when a cat is waking up from sleep, it looks like a white sheet that emerges from the sides.

This eyelid automatically closes when something is aimed at the eye. So if the cat is walking inside a bush with lots of poking branches, it will use this second eyelid to protect the cornea from being damaged.

Cool right?

Post 6

I've been thinking about getting laser eye surgery to fix my eye sight but after I learned about what they actually do in the surgery, I've been very scared.

My doctor said that this surgery involves cutting a flap from the top of the cornea. After they remove this flap, they use laser to make changes in the cornea itself to fix eye sight and then they put the flap of cornea back.

Isn't this really dangerous? Does our cornea have the capacity to fix itself after it has been cut like that?

Post 5

I had no idea that our eyes were so complex.

I'm curious, are the eyes of animals structured the same way as ours? Do they have the same parts?

Post 2

Great article- I just want to add that a good way to protect the retina is to purchase polarized sunglasses.

Polarized sunglasses protect the eyes and especially the retina from the harmful UVA and UVB rays. It allows you to see objects clearly without any form of glare.

It is well known that prolonged exposure to UVB rays can lead to photokeratitis which is a sunburn in the eyes. This sun exposure burns the cornea. This is another reason why polarized glasses are so important.

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