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GLOSSARY

    Anterior uveitis

    Anterior uveitis is an inflammation of the iris (colored part of the eye) and adjacent tissue, known as the ciliary body. It can occur as a result of trauma to the eye, such as a blow or foreign body penetrating the eye. It can also be a complication of other eye disease, or it may be associated with general health problems.

    Blepharitis

    Blepharitis is a chronic or long term inflammation of the eyelids and eyelashes. It affects people of all ages. Among the most common causes of blepharitis are poor eyelid hygiene; excessive oil produced by the glands in the eyelid; a bacterial infection (often staphylococcal); or an allergic reaction.

    Cataract

    A cataract is a clouding of all or part of the normally clear lens within your eye, which results in blurred or distorted vision. Cataracts are most often found in persons over age 55, but they are also occasionally found in younger people.

    A chemical change occurs within your eye to cause the lens to become cloudy. This may be due to advancing age, heredity or an injury or disease. Excessive exposure to ultraviolet radiation in sunlight, cigarette smoking or the use of certain medications are also risk factors for the development of cataracts.

    Conjunctivitis

    Conjunctivitis is an inflammation of the conjunctiva, the thin, transparent layer that lines the inner eyelid and covers the white part of the eye. The three main types of conjunctivitis are infectious, allergic and chemical.

    Diabetic Retinopathy

    Diabetes is a disease that interferes with the body's ability to use and store sugar and can cause many health problems. One, called diabetic retinopathy, can weaken and cause changes in the small blood vessels that nourish your eye's retina, the delicate, light sensitive lining of the back of the eye. These blood vessels may begin to leak, swell or develop brush-like branches.

    The early stages of diabetic retinopathy may cause blurred vision, or they may produce no visual symptoms at all. As the disease progresses, you may notice a cloudiness of vision, blind spots or floaters.

    Early treatment is important because once damage has occurred, the effects are usually permanent. It is important to have your eyes examined regularly by your doctor of optometry. This is especially true if you are a diabetic or if you have a family history of diabetes.

    Dry eyes

    The tears your eyes produce are necessary for overall eye health and clear vision. Dry eye means that your eyes do not produce enough tears or that you produce tears which do not have the proper chemical composition. There are other reasons for dry eyes, but often, it is part of the natural aging process.

    Glaucoma

    Glaucoma is an eye disease in which the internal pressure in your eyes increases enough to damage the nerve fibers in your optic nerve and cause peripheral vision loss. Late stages of glaucoma will also have central vision loss. Vision lost to glaucoma cannot be restored.
    People with a family history of glaucoma, African Americans, and those who are very nearsighted or diabetic are at a higher risk of developing the disease. The most common type of glaucoma develops gradually and painlessly, without symptoms.

    Keratoconus

    Keratoconus is a vision disorder that occurs when the normally round cornea (the front part of the eye) becomes thin and irregular (cone) shaped. This abnormal shape prevents the light entering the eye from being focused correctly on the retina and causes distortion of vision.

    Macular Degeneration

    Macular degeneration results from changes to the macula, a portion of the retina that is responsible for clear, sharp vision and is located at the back of the eye. Causes are hereditary and/or environmental. Central vision that is lost to macular degeneration cannot be restored. However, low vision devices can be prescribed to make the most out of remaining vision.

    Ocular Hypertension

    Ocular hypertension is an increase in the pressure in your eyes that is above the range considered normal with no detectable changes in vision or damage to the structure of your eyes. Ocular hypertension has no noticeable symptoms. The term is used to distinguish people with elevated pressure from those with glaucoma, a serious eye disease that causes damage to the optic nerve and vision loss. There is an increased risk of glaucoma among those with ocular hypertension.

    Retinitis Pigmentosa

    Retinitis pigmentosa (RP) is a group of inherited diseases that damage the light-sensitive rods and cones located in the retina, the back part of our eyes. Rods, which provide side (peripheral) and night vision are affected more than the cones which provide color and clear central vision.

    Usually during childhood or adolescence, the first sign is often night blindness followed by a slow but progressive loss of side vision.

    Also, there are many new low vision aids that are available that help people maximize the vision that they have remaining.

 

The Anatomy of the Eye

                              Eye to Eye

Even though the eye is small, only about 1 inch in diameter, it serves a very important function - your sense of sight. Vision is arguably the most used of the 5 senses and is one of the primary means that we use to gather information from our surroundings.

The eye is often compared to a camera. Each gathers light and then transforms that light into a “picture.” Both also have lenses to focus the incoming light. A camera uses the film to create a picture, whereas the eye uses a specialized layer of cells, called the retina, to produce an image.

Orbit

The orbit is the eye socket, which is formed by the cheekbone, the forehead, the temple, and the side of the nose. The eye is cushioned within the orbit by pads of fat.

The orbit also contains the lacrimal gland that is located underneath the outer portion of the upper eyelid. The lacrimal gland produces tears that help lubricate and moisten the eye, as well as flush away any foreign matter that may enter the eye. The tears drain away from the eye through the nasolacrimal duct, which is located at the inner corner of the eye.

Conjunctiva

The conjunctiva is a thin, clear layer of skin covering the front of the eye, including the sclera and the inside of the eyelids. The conjunctiva keeps bacteria and foreign material from getting behind the eye.

Sclera

The white part of your eye that you see when you look at yourself in the mirror is the front part of the sclera. However, the sclera, a tough, leather-like tissue, also extends around the eye. Just like an eggshell surrounds an egg and gives an egg its shape, the sclera surrounds the eye and gives the eye its shape.

The sclera is also attached to the extraocular muscles, which, in turn, move the eye left and right, up and down, and diagonally.

Cornea

The cornea is a clear layer at the front and center of the eye. In fact, the cornea is so clear that you may not even realize it is there. The cornea is located just in front of the iris, which is the colored part of your eye. The main purpose of the cornea is to help focus light as it enters the eye. If you wear contact lenses, the contact lens rests on your cornea.

Anterior Chamber

The anterior chamber is the fluid-filled space immediately behind the cornea and in front of the iris. The fluid that fills this chamber is called the aqueous humor. The aqueous humor helps to nourish the cornea and the lens.

Iris and Pupil

The iris, which is the colored part of your eye, controls the amount of light that enters the eye. The iris is a ring shaped tissue with a central opening, which is called the pupil.

The iris has a ring of muscle fibers around the pupil, which, when contracted, causes the pupil to constrict (become smaller) in bright light. Another set of muscle fibers radiate outward from the pupil, which causes the pupil to dilate (become larger) in dim light or darkness.

Anterior Chamber Angle/Trabecular Meshwork

The anterior chamber angle and the trabecular meshwork are located where the cornea meets the iris. The trabecular meshwork is important because it is the site where the aqueous humor drains out of the eye. If the aqueous humor cannot properly drain out of the eye, the pressure can build up inside the eye, causing optic nerve damage and eventually vision loss, a condition known as glaucoma.

Posterior Chamber

The posterior chamber is the fluid-filled space immediately behind the iris but in front of the lens. The fluid that fills this chamber is called the aqueous humor. The aqueous humor helps to nourish the cornea and the lens.

Lens

The lens is a clear, flexible structure that is located just behind the iris and the pupil. A ring of muscular tissue, called the ciliary body, surrounds the lens. Together, the lens and the ciliary body help control fine focusing of light as it passes through the eye.

Vitreous Cavity

The vitreous cavity is located behind the lens and in front of the retina. It is filled with a gel-like fluid, called the vitreous humor. The vitreous humor helps maintain the shape of the eye.

Retina/Macula/Choroid

The retina acts like the film in a camera to create an image. To do this, the retina, a specialized layer of cells, converts light signals into nerve signals. After light signals are converted into nerve signals, the retina sends these signals to the optic nerve, which carries the signals to the brain. There, the brain helps process the image.

The retina is primarily made up of 2 distinct types of cells: rods and cones. Rods are more sensitive to light; therefore, they allow you to see in low light situations but do not allow you to see color. Cones, on the other hand, allow you to see color but require more light.

The macula is located in the central part of the retina. It is the area of the retina that is responsible for giving you sharp central vision.

The choroid is a layer of tissue that separates the retina and the sclera. It is mostly made up of blood vessels. The choroid helps nourish the retina.

Optic Nerve

The optic nerve, a bundle of over 1 million nerve fibers, is responsible for transmitting nerve signals from the eye to the brain. These nerve signals contain information on an image for processing by the brain. The front surface of the optic nerve, which is visible on the retina, is called the optic disk.

Extraocular Muscles

Six extraocular muscles are attached to each eye to help move the eye left and right, up and down, and diagonally.

Sources: Lauri Graham, Medical Writer, eMedicine.com, Inc.

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