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Take a Tour of the Eye

Dictionary of Terms

The eye is a complex part of the human anatomy. Learn about the retina, the cornea, and other parts of your eye, as well as basic descriptions of some common eye ailments such as retina disease.

This list will help you with the terminology.

The Eye

We are able to see by the light rays that are reflected off an object and through the eyeball. These light rays are focused upside-down on the retina where it is converted to electrical impulses and carried to the brain. The brain translates the image into its upright position.

Anterior chamber

Space in the front portion of the eye between the cornea and the iris and lens, which is filled with aqueous.

Aqueous

The clear fluid between the anterior chamber and posterior chamber that is produced by the ciliary body. Aqueous is important in controlling the pressure inside the eye and giving the front of the eye its shape.

Choroid

The middle layer of the eye, located between the sclera and the retina. It contains several layers of blood vessels that provide crucial support to other parts of the eye. The choroid, along with the iris and ciliary body, are collectively known as the uvea. Inflammation in this area is known as uveitis.

Ciliary body

A ring of tissue between the iris and the choroid consisting of muscles and blood vessels that changes the shape of the lens and manufactures the aqueous.

Cones

Cone-shaped light-sensitive cells in the retina, particularly the part known as the macula. The cones are mostly used during daylight, when pupils are small, to allow a person to see details and shapes, especially colors.

Conjunctiva

The mucous membrane that is on the inside of eyelids and on the surface of the eyeball as well as the sclera (the “white of the eye.”) When the conjunctiva becomes irritated or inflamed, it is known as conjunctivitis. One common type of conjunctivitis that many people experience is “pink eye.” Conjunctivitis can be present in just one eye, or it can affect both eyes. Symptoms include redness of the eyes or the edges of the eyelids, swelling of the eyelids or itching. Giant papillary conjunctivitis is when bumps or ridges form on the inside of eyelids, making contact lens wear uncomfortable.

Cornea

The transparent structure on the front of the eye through which we see. It is the tissue that is reshaped during laser vision correction. It begins the process of seeing by focusing onto the retina the light that it receives. There are five layers to the cornea, each with a distinct function: epithelium, Bowman’s membrane, stroma, Descemet’s membrane and endothelium.

Extraocular muscles

The tiny muscles that surround the eye and control its movements. There are six: the lateral rectus, medial rectus, superior oblique, inferior oblique, superior rectus and inferior rectus. The primary function of the four rectus muscles is to control the eye’s movements from left to right and up and down. The two oblique muscles rotate the eyes inward and outward. All six muscles work in unison; when they do not function properly, the condition is called strabismus. Ophthalmologists can present several options for correcting strabismus.

Fovea

The very center of the macula, which itself is a small part of the retina. The fovea is important because it has many of the cells that allow color vision.

Iris

The “color” of our eyes. The iris responds to changing amounts of light by altering pupil size (bigger in less light, smaller in more light).

Lens

Housed behind the iris, the lens is the second component that focuses light rays. Light rays that pass through the lens travel through the vitreous onto the retina. When the lens becomes clouded, it is called a cataract. Surgery for cataracts involves removing this clouded lens and, usually, replacing it with a man-made one.

Macula

The area of the retina responsible for the center of our vision. The macula often deteriorates as we age, causing age-related macular degeneration. Many patients with this condition lose some or all of their ability to see straight ahead, and are left with only peripheral (side) vision. Several retina specialists at The Cole Eye Institute treat wet and dry macular degeneration.

Optic Disc

The head of the optic nerve that is formed by the meeting of all retinal nerve fibers.

Optic Nerve

The path from the eye to the brain. The electronic impulses that are developed by the retina are imbedded in the brain’s visual cortex, thus creating a visual image. It is the largest ocular nerve and is crucial to vision. Glaucoma is one disease that damages the optic nerve.

Physiologic Blind spot

The area of the optic disk where the optic nerve fibers exit the eye and where there are no light-sensitive cells.

Punctum

The hole in the upper and lower eyelids through which tears exit the eye. In patients with dry eyes, temporary or permanent plugs may be inserted to help keep tears in the eye. Tears flow through the punctum to the nose, which is why people often experience a runny nose when crying.

Pupil

The black central part of the iris that changes size in response to how much light is being received by the eye.

Retina

A thin lining that is the back inner part of the eye. Its light-sensitive cells convert the image that is focused through the cornea and lens to electronic impulses. These impulses are then passed through the optic nerve.

Rods

Cells in the retina that enable vision in darkness or dim light.

Sclera

The area commonly referred to as the white of the eye.

Uvea

The colored, middle layers of the eye. It includes the iris (colored part of the eye), choroid (a thin membrane containing many blood vessels) and ciliary body (the part of the eye that joins these together). The uvea is very important because its veins and arteries transport blood to the parts of the eye that are critical for vision. Inflammation in this part of the eye is known as uveitis.

Vitreous

The gelatinous matter between the lens and the retina. It is what is removed during “vitrectomy,” a procedure used in treating some retinal problems. When people see moving specks in their vision often described as “floaters,” this is usually where they are located.

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This information is provided by Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition.

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