Anatomy of the Eye Glossary of Terms

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Anatomy: The study of form. Gross anatomy involves structures that can be seen with the naked eye. It is as opposed to microscopic anatomy (or histology) which involves structures seen under the microscope. Traditionally, both gross and microscopic anatomy have been studied in the first year of medical school in the U.S. The most celebrated textbook of anatomy in the English-speaking world is Gray's Anatomy, still a useful reference book. The word "anatomy" comes from the Greek ana- meaning up or through + tome meaning a cutting. Anatomy was once a "cutting up" because the structure of the body was originally learned through dissecting it, cutting it up. The abbreviation for anatomy is anat.

Anterior: The front, as opposed to the posterior. The anterior surface of the heart is toward the breast bone (the sternum).
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Anterior chamber: The space in the eye that is behind the cornea and in front of the iris.
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Aqueous humor: In medicine, humor refers to a fluid (or semifluid) substance. Thus, the aqueous humor is the fluid normally present in the front and rear chambers of the eye. It is a clear, watery fluid that flows between and nourishes the lens and the cornea; it is secreted by the ciliary processes.
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Bacteria: Single-celled microorganisms which can exist either as independent (free-living) organisms or as parasites (dependent upon another organism for life).
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Brain: That part of the central nervous system that is located within the cranium (skull). The brain functions as the primary receiver, organizer and distributor of information for the body. It has two (right and left) halves called "hemispheres."

Central vision: Straight-ahead vision. Central vision is the work of the macula, a small area in the center of the retina that contains a rich collection of cones. (The retina is made up of two types of cells, the cones and the rods. Millions of cones are packed into the macula. The cones are nerve cells sensitive to light, fine detail, and color.) Central vision permits a person to read, drive, and perform other activities that require fine, sharp, straight-ahead vision. As opposed to peripheral vision.

Choroid: In the eye, a thin vascular layer between the sclera and the retina. The choroid supplies blood to the retina and conducts arteries and nerves to other structures in the eye.

Ciliary body: Part of the eye, the ciliary body is a thin vascular (blood vessel-filled) middle layer of the eye that is situated between the sclera (the white of the eye) and the retina (the nerve layer that lines the back of the eye, senses light, and creates impulses that travel through the optic nerve to the brain).
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Conjunctiva: A thin clear moist membrane that coats the inner surfaces of the eyelids and the outer surface of the eye.
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Cornea: The clear front window of the eye that transmits and focuses light into the eye.
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Dilate: To stretch or enlarge. It comes from the Latin verb "dilatare" meaning "to enlarge or expand."

Drain: A device for removing fluid from a cavity or wound. A drain is typically a tube or wick. As a verb, to allow fluid to be released from a confined area.

Duct: A passage or a tube with well-defined walls suitable for the conveyance of air or liquids, as the bile duct and the pancreatic duct.
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Eyelid: The lid or cover of the eye, a movable fold of skin and muscle that can be closed over the eyeball or opened at will. Each eye has an upper and a lower lid. An eyelid is also called a palpebra.

Flush: (1) A redness of the skin, typically over the cheeks or neck. A flush is usually temporary and brought on by excitement, exercise, fever, or embarrassment. Flushing is an involuntary (uncontrollable) response of the nervous system leading to widening of the capillaries of the involved skin. Also referred to as a blush (or, as a verb, to blush). Flushing may also be caused by medications or other substances that cause widening of the capillaries, such as niacin. (2) Flush also means to wash out a wound or body area.

Gland: 1. A group of cells that secrete a substance for use in the body. For example, the thyroid gland. 2. A group of cells that removes materials from the circulation. For example, a lymph gland.

Glaucoma: A common eye condition in which the fluid pressure inside the eyes rises because of slowed fluid drainage from the eye. If untreated, it may damage the optic nerve and other parts of the eye, causing the loss of vision or even blindness.
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Humor: In medicine, humor refers to a fluid (or semifluid) substance. Thus, the aqueous humor is the fluid normally present in the front and rear chambers of the eye. The humors ran through an ancient theory that held that health came from balance between the bodily liquids. These liquids were termed humors. Disease arose when there was imbalance between these humors.
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Iris: The iris is the circular, colored curtain of the eye. Its opening forms the pupil. The iris helps regulate the amount of light that enters the eye.
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Lacrimal: Pertaining to tears, as in lacrimal gland (tear gland). From the Indo-European dakru meaning a tear (from a weeping eye) which gave rise to the Greek dakry and the Latin lacrima.

Lacrimal gland: A small almond-shaped structure that produces tears. The lacrimal gland is located just above the outer corner of the eye. The lacrimal gland is part of the lacrimal apparatus, the system that forms tears, conveys them through the lacrimal (tear) duct to the eye, and drains the tears.
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Lens: The transparent structure inside the eye that focuses light rays onto the retina (the nerve layer that lines the back of the eye, senses light and creates impulses that go through the optic nerve to the brain). The lens was named after the lentil bean because it resembled it in shape and size.
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Macula: A macula is a small spot. A macula on the skin is a small flat spot while the macula in the eye is a small spot where vision is keenest in the retina.

Muscle: Muscle is the tissue of the body which primarily functions as a source of power. There are three types of muscle in the body. Muscle which is responsible for moving extremities and external areas of the body is called "skeletal muscle." Heart muscle is called "cardiac muscle." Muscle that is in the walls of arteries and bowel is called "smooth muscle."

Muscular: Having to do with the muscles. Also, endowed with above average muscle development. Muscular system refers to all of the muscles of the body collectively.

Nerve: A bundle of fibers that uses chemical and electrical signals to transmit sensory and motor information from one body part to another. See: Nervous system.

Nose: The external midline projection from the face.
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Ophthalmologist: An eye doctor. A physician practicing ophthalmology. An ophthalmologist is an M.D.

Ophthalmology: The art and science of eye medicine.

Optic: Having to do with vision.

Optic nerve: The optic nerve connects the eye to the brain. The optic nerve carries the impulses formed by the retina, the nerve layer that lines the back of the eye and senses light and creates impulses. These impulses are dispatched through the optic nerve to the brain, which interprets them as images. Using an ophthalmoscope, the head of the optic nerve can be easily seen. It can be viewed as the only visible part of the brain (or extension of it).
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Orbit: In medicine, the bony cavity in which the eyeball sits together with its associated muscles, blood vessels, and nerves. The orbit is formed of parts of the ethmoid, frontal, lacrimal, nasal, palatine, sphenoid, and zygomatic bones and the maxilla.

Orbital: Relating to the orbit, in anatomy the bony cavity that contains the eyeball.

Pharmacy: A location where prescription drugs are sold. A pharmacy is, by law, constantly supervised by a licensed pharmacist.

Posterior: The back or behind, as opposed to the anterior.
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Posterior chamber: The space in the eye behind the iris and in front of the lens. (The iris is the colored ring of tissue that regulates the amount of light entering the eye by adjusting the size of the pupil. The lens is the transparent biconvex body in the eye that refracts light. By "biconvex" is meant that it is convex, that it protrudes, on both sides.)
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Pupil: The opening of the iris. The pupil may appear to open (dilate) and close (constrict) but it is really the iris that is the prime mover; the pupil is merely the absence of iris. The pupil determines how much light is let into the eye. Both pupils are usually of equal size. If they are not, that is termed anisocoria (from "a-", not + "iso", equal + "kore", pupil = not equal pupils).
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Radiate: To spread out from a central area. For example, sciatic pain may radiate outward from the lower back.

Retina: The retina is the nerve layer that lines the back of the eye, senses light, and creates impulses that travel through the optic nerve to the brain. There is a small area, called the macula, in the retina that contains special light-sensitive cells. The macula allows us to see fine details clearly.
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Sclera: The tough white outer coat over the eyeball that covers approximately the posterior five-sixths of its surface. The sclera is continuous in the front of the eye with the cornea and in the back of the eye with the external sheath of the optic nerve.
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Surgery: The word "surgery" has multiple meanings. It is the branch of medicine concerned with diseases and conditions which require or are amenable to operative procedures. Surgery is the work done by a surgeon. By analogy, the work of an editor wielding his pen as a scalpel is s form of surgery. A surgery in England (and some other countries) is a physician's or dentist's office.
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Temple: An area just behind and to the side of the forehead and the eye, above the side of the check bone (the zygomatic arch) and in front of the ear.
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Vitreous: A clear, jelly-like substance that fills the middle of the eye. Also called the vitreous humor, "humor" in medicine referring to a fluid (or semifluid) substance.