Overview

What are the eyes?

Your eyes are organs that allow you to see. They take in light from the world around you and send visual information to your brain. Your eyes can see about 200 degrees in all directions, including in front of you and to the sides (peripheral vision). Parts of your eyes work together to allow you to see images, movement and depth. Your eyes can see millions of colors in varying shades.

Many conditions can affect how your eyes work, including common vision problems like myopia (nearsightedness), astigmatism and eye injuries. Several diseases and disorders that are not necessarily eye-related can cause problems in the eyes, including autoimmune disorders, diabetes and high blood pressure.

To keep your eyes healthy, you should see your provider for regular eye exams. Eat a balanced diet, maintain a healthy weight and avoid smoking, which can damage your eyes. Always wear protective eyewear to prevent injuries, especially during contact sports or if you have a job working with tools that could potentially lead to eye injuries (welding, metalwork, woodworking, etc).

Function

What are the parts of the eye?

The parts of the eye include:

Iris, the colored area of your eye. Depending on your eye color, the iris might be any shade of blue, green, hazel or brown.
Cornea, a clear layer that extends over the iris. Water and collagen make up the cornea. Your tears protect your cornea and keep it lubricated.
Pupil, the black circle which is an opening or window in the middle of your iris. It expands and contracts to control how much light gets into your eye.
The sclera, the white parts of your eye that surround the iris.
Conjunctiva, a clear, thin tissue that covers the sclera and lines the inside of your eyelids.
Lens, which sits behind the pupil. It focuses the light that comes into your eye and sends light to the back of your eye.
Retina, a collection of cells that line the inside of the back of your eye. Part of your nervous system, the retinas sense light and convert it into electrical impulses or neural signals. The retina has rods (cells that help you see in low light) and cones (cells that detect color).
Macula, a small area that’s part of the retina. It’s responsible for central vision and helping you see fine details and color.
Optic nerve, which is behind the retina. It carries signals from the retina to your brain which then interprets that visual information to tell you what you are seeing.
Muscles, which control your eye’s position and movement, how much light gets into your eye and your eyes’ ability to focus.
Vitreous, a transparent gel that fills your entire eye. It protects and maintains the shape of the eye.

How do your eyes work?

The different parts of your eye work together to help you see images and send visual information to your brain. This process all happens extremely quickly. When you look at an object:

Light enters your eye through the cornea and goes to your lens. Your pupil gets bigger and smaller to control the amount of light that gets into your eye.
Your cornea and lens refract (bend) the light to bring what you’re seeing into focus.
Light reaches the retina at the back of your eye, and the retina changes the images into electrical impulses or signals.
The optic nerve transfers these signals to the part of your brain that’s responsible for vision (visual cortex). The optic nerve carries signals from both eyes at once.
Your brain interprets what you’ve seen. It combines the visual information from both eyes and brings it all together into one clear image.

Anatomy

What does the eye look like?

Your eye is the shape of a ball that’s slightly compressed. It’s not quite a perfect sphere because it’s a little more pointed in the front. In adults, the eye is about 1 inch in diameter.

Eye colors vary, from blue, green or amber to all shades of brown. Some people have flecks or stripes of different colors in their irises. They may also have a darker ring of color around their irises. The color of your eyes depends on your genes.

Conditions and Disorders

What conditions affect how the eyes work?

There are hundreds of conditions, disorders, diseases and injuries that affect the eyes. Some conditions, such as uveitis, cause eye pain. Others can lead to low vision or vision loss. About 12 million adults in the United States have some type of impaired vision.

Conditions that affect the eyes include:

Age-related changes in vision: Your eyes change as you age. Many people get floaters and flashers. In some cases, cataracts, macular degeneration or a detached retina can occur as you get older. Presbyopia (losing near-focus vision) usually starts to affect people around age 45.
Cancer: Tumors can result from intraocular melanoma and retinoblastoma.
Disease: Many types of eye disease can affect the eyes, including congenital (present at birth) cataracts, glaucoma and optic atrophy. Corneal disease includes many diseases that affect the cornea. Optic neuritis causes inflammation in the optic nerve.
Infection and irritation: Pink eye (conjunctivitis), blepharitis, a sty (stye), chalazion and dry eyes cause redness, swelling and discomfort. Watery eyes can result when the eye doesn’t drain tears properly or the eyes are irritated or dry.
Inherited disorders: Retinitis pigmentosa is an inherited condition (passed down through families) that can lead to blindness.
Injuries: Corneal abrasions and a detached retina can result from trauma to the eye. Accidents can cause eye bleeding, a black eye, burns and irritation. Foreign objects can also damage the eye.
Problems with the muscles in the eyes: Strabismus (crossed eyes) or amblyopia (lazy eye) can cause changes in how the eyes appear. They can also lead to vision changes.
Vision problems: Astigmatism and hyperopia (farsightedness) affect how the eye refracts (bends) light and brings images into focus. Color blindness makes it difficult or impossible to see different colors. Conversion insufficiency affects the eyes’ ability to work together. Some people have problems seeing at night.

Some conditions affect the eyes directly. Other disorders begin in different parts of your body and lead to problems in your eyes. These include:

Autoimmune disorders, including lupus, thyroid eye disease, Sjörgren’s syndrome and multiple sclerosis (MS).
Cardiovascular problems such as arterial disease, high blood pressure and high cholesterol.
Diabetes, which can lead to diabetes-related retinopathy.
Genetic disorders such as Marfan syndrome.

What are some common signs or symptoms of eye conditions?

Signs of eye problems include:

Eye pain, redness, swelling, bleeding or discharge.
Eyes that cross or point in different directions.
Eyes that sting, itch, burn or are very dry.
Flashes of light, especially in your peripheral (side) vision.
Headaches and squinting.
Inability to move your eyes or open or close your eyelid.
Many spots or one dark spot in the middle of your field of vision.
Sensitivity to light or trouble seeing in low light.
Vision changes, including cloudy or blurry vision and double vision.

What are common tests to check the health of the eyes?

During a comprehensive eye exam, providers use several tests to check for disease and other problems in the eye. Depending on your symptoms, your provider may recommend tests that evaluate your field of vision, visual acuity (sharpness) or ability to see color. They may also check the pressure inside your eye or use imaging studies to get a closer look at your retina or optic nerve.

What are some common treatments for conditions that affect the eyes?

Treatments for eye problems vary widely. They include:

Corrective lenses: Glasses or contact lenses help you see clearly. Your provider may also recommend vision correction surgery. People with presbyopia can use special reading glasses to help with up-close vision.
Eyedrops or an eye patch: If you have an eye injury, your provider may recommend flushing out your eye with water. You may also need eye drops or an eye patch so your eye can heal.
Medications: Your provider may recommend antibiotics to treat infection. You may need other drugs to manage a health condition that’s causing eye problems.
Surgery: Depending on your symptoms, you may need cataract surgery or a procedure to reattach a retina. Providers also perform surgery to correct crossed eyes, remove tumors or transplant a cornea.

Care

How can I keep my eyes healthy?

To keep your eyes healthy, you should:

Get regular eye exams so your provider can monitor your health and detect eye problems early.
Maintain a healthy weight, eat a balanced diet and quit smoking if you smoke.
Wear protective glasses during contact sports, when working with chemicals or when doing activities that might damage your eyes, such as using fireworks.

Frequently Asked Questions

When should I call my doctor about my eyes?

Get medical help right away if you or your child has:

An eye injury, especially if the eye is red, swollen, bruised or bleeding.
A foreign object in the eye (don’t try to remove it).
Bulging eye or eyes (proptosis).
Cloudy or blurry vision, or if you feel like there is a veil over your field of vision.
Eye-related symptoms along with vomiting, chills or fever.
Flashes of light in your peripheral (side) vision, halos surrounding lights or a dark spot or floater in the center of your field of vision.
Problems moving the eyes in all directions.
Sudden vision changes.

A note from Cleveland Clinic

Your eyes play a critical role in helping you interact with the world. The parts of the eye work together to allow you to see. Many injuries, diseases and conditions can cause problems with how the eyes work. If you or your child has headaches or you’re squinting to see, call your provider for an eye exam. Get help right away if you see flashes of light or a new floater. You should also call your provider if your vision is suddenly cloudy, blurry or if you’re seeing double. These may be signs of a serious eye problem. To keep your eyes healthy, protect them during activities that could cause damage.

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Eyes