Did you ever think about all the things your eyes do? Eyes let you read a cereal box, check out a rainbow, see a softball coming, cry when sad, makes tears to protect itself, and eyes have muscles and a lens that adjust to let you focus on things that are up close or far away. Your eyes provide information about depth, distance, shape, color, and movement of objects. We depend on our sight more than any other of our senses and amazingly, 80% of what we perceive comes through our eyes; and our memories are 80% imagery.

Look at all the colors! Did you know that the human eye can detect 10 million color hues but cannot see ultraviolet or infrared light? Ultraviolet light has a wavelength that is shorter than the visible violet wavelength in the color spectrum, so we can’t see it. Infrared has a wavelength longer than the visible red wavelength in our spectrum so we can’t see this type of light either. Interestingly, insects can see ultraviolet light.

Seeing - How it happens

Light rays enter our eyes, pass through the cornea, pupil and lens and are focused onto the retina. The retina sends these light impulses to the brain through the optic nerve and the brain then translates all the information into the images we see.

Sometimes the shape of our eyeballs makes it difficult for the cornea, lens and retina to work together perfectly as a team. When this happens, some of what person sees can be out of focus and we have a need for glasses or contacts to help the eyes focus and see clearly. With glasses or ‘corrective lenses’ the team works together beautifully and our sight is improved.

10 Essentials of Eye Anatomy

Part 1: The Sclera

The sclera is the white part of the eyeball and is responsible for covering most of the eyeball. It is made of a very tough material. Think of it like your outer coat. If you look very closely at the sclera, you will see lines that look like tiny pink threads -- these are blood vessels that deliver blood and nourishment to the sclera.

Part 2: Extraocular Eye Muscles

To see fully, the eye has to move. There are six extraocular muscles (EOMS) attached to each eye that enable the eyes to have a full range of movement – up, down, and side to side. The muscles of each eye normally move together at the same time and allow the eyes to be aligned. These muscles also hold the eye in position.

Part 3: The Cornea

The cornea is the transparent dome that covers, or sets over, the colored part of the eye. It is like a window through which we view the world. The cornea is very important because it, along with the lens, refracts and focuses the light that comes in through our eyes. The cornea takes care of 70% of the refraction and focusing process.

Part 4: The Iris

The iris is the colored part of our eyes and when we say ‘brown eyes’ for example, we are really referring to brown irises. The iris is made up of muscles and tissues that adjust the size of the pupil so the appropriate amount of light can travel through pupil and form an image on the retina. The iris is like the aperture function a camera.

Part 5: The Pupil

The pupil is the black circle in the center of the iris. It is like a gate that opens and closes adjusting the amount of light that enters our eyes helping to form images on the retina. A larger pupil lets more light pass through the eye, which is very helpful in dim light, and a smaller pupil lets less light reach the retina, such as in the day time or bright sunlight. The average diameter of the pupil is approximately 3 millimeters. The pupil is regulated by the brain and when the doctor checks the reaction of your pupils to light, they have a basic idea of how your brain is functioning.

Part 6: The Lens

The lens is located behind the iris and is clear, colorless, and made up of proteins. Its job, along with the cornea, is to refract and focus light rays coming into our eyes onto the retina. The lens takes care of 30% of the refraction and focusing process. The lens is located behind the iris and is surrounded by fibers called zonules. These zonules change the shape of the lens to accommodate shifts in our vision from near to far.

Part 7: The Retina, Rods, and Cones

The retina is like a film screen. It is located in the very back of the eye and has millions of cells that are sensitive to light. As light comes in, the retina changes it to nerve signals and sends those signals to the brain through the optic nerve. In order to process light, the retina uses special photoreceptors called rods and cones. Imagine – in each eye, there are 120 million rods and 7 million cones!

Rods are super sensitive and see only black, white, and shades of gray; they are not sensitive to color. They are particularly helpful with night vision. Rods also help to discern the form or shape of something and assist with peripheral vision. Rods thrive on vitamin A and that’s why carrots, cabbage and other green vegetables benefit the eye.

Cones are active at higher levels of light and are responsible for seeing color, finely-detailed mages, and more rapid changes in images.

Part 8: The Vitreous Body

The vitreous body is the biggest part of the eye accounting for 2/3 of the eye’s volume. It sits behind the lens and gives eye its shape. This part of the eye is filled with a clear jelly-like substance called the vitreous humor. After light comes in through lens, it goes straight through the vitreous humor to back of eye.

Part 9: The Optic Nerve

You might call this part of the eye the ‘great messenger.’ The optic nerve is a collection of nerve fibers that takes all the information from the retina and carries it to the brain. It’s kind of like a high-speed telephone line connecting the eye to the brain. When light enters our eyes and we see an image, the retina ‘telephones’ the brain with a report made up of impulses. The brain translates these impulses into the images and details that we see.

Part 10: The Lacrimal Glands, and Eyelids

The eye has its own built-in cleansing and protection system in the form of blinking and tears. The reflex of blinking our eyelids helps keep dirt, dust, and harmful bright light out of our eyes. Each time we blink, our eyelids spread a layer of moisture consisting of mucus, oil, and tears over our eyes so that they are cleansed and moistened. It is the lacrimal glands, located in the upper outer corner of each eye, that produce tears. After the tears have moistened the eyes, they flow into canals in the eyelids called the lacrimal sac that is located in the lower corner of each eye.

The Fact Is…

Although the eyes are small in size compared with the rest of the body’s organs, their anatomy and processes are extremely complex. The eyes not only work together with each other, they also work in tandem with the brain, muscles and nerves to help us see and interpret the world around us. Whether it’s just a glance, a short look, or a long-time observation, it’s plain to see that our eyes are invaluable.

The Ophthalmic Physicians Team - Caring for your Vision!

Please publish modules in offcanvas position.