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All about Your Eyes
     

All about Your Eyes

by Sharon Fekrat (Editor), Jennifer S. Weizer (Editor), Paul P. Lee (Contribution by), Ravi Chandrashekhar (Contribution by)
 

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A concise, easy-to-understand reference book, All about Your Eyes tells you what you need to know to care for your eyes and what to expect from your eye doctor.

In this reliable guide, leading eye care experts:
—explain how healthy eyes work
—describe various eye diseases, including pink eye, cataract, glaucoma, age-related macular

Overview

A concise, easy-to-understand reference book, All about Your Eyes tells you what you need to know to care for your eyes and what to expect from your eye doctor.

In this reliable guide, leading eye care experts:
—explain how healthy eyes work
—describe various eye diseases, including pink eye, cataract, glaucoma, age-related macular degeneration, and diabetic retinopathy
—provide up-to-date information on eye surgery, including refractive, laser, and cosmetic

For each eye problem, the authors describe in simple, straightforward language
—what it is
—the symptoms
—what, if anything, you can do to prevent it
—when to call the doctor
—the treatment
—the likelihood of recovery

All about Your Eyes includes a glossary of technical terms and, following each entry, links to web sites where further information may be found.

Editorial Reviews

From the Publisher
“As an athlete and a coach, I have long had a keen appreciation for how important our eyes are to almost everything we do. Whether you’re a writer or gardener, a grad student or grandparent, this clear and helpful book gives you all the information necessary to get peak performance from your eyes.”—Dr. LeRoy Walker, past president of the U.S. Olympic Committee and member of the U.S. Olympic Hall of Fame
Archives of Opthamology - Leslie Weingeist France
“Although this book is written to provide such information to [patients], it also serves as yet another important resource for workers in eye care who need to be able to explain things in a simple and succinct way. Why not require that it be read by all who will have to deal with patients, be they ophthalmic assistants, photographers, ophthalmic nurses, triage nurses, receptionists, schedulers, or residents? For many, this book will simply be a review; for others, it will be a concise, informative introduction. A copy of the book might be available in the waiting areas of the clinics for patients and their families and in the nursing, ophthalmic technician, and scheduling areas for easy reference. . . . It is a quick read and I highly recommend it.”
Library Journal
Vitreoretinal surgeon Fekrat (ophthalmology, Duke Univ.) and Weizer (ophthalmology & visual sciences, Kellogg Eye Ctr., Univ. of Michigan) have edited a concise reference book to educate readers and help them get the most out of their professional eye consultations. The contributing physicians and medical practitioners devote the greatest coverage to specific eye ailments; one- to two-page overviews of particular conditions list definitions, symptoms, diagnoses, treatments, and one or two reputable related web sites. Other chapters address eye anatomy, vision problems, and the latest eye surgery techniques. The glossary is adequate, but some definitions are sketchy and others too technical; likewise, the occasional anatomical diagrams could be better detailed. Overall, despite some incomplete procedural explanations and undefined terms, this is a good introduction. Another option: Mayo Clinic on Vision and Eye Health covers fewer ailments but is written less technically and is extensively illustrated. All About Your Eyes is recommended for consumer health and public libraries.-Janice Flahiff, Medical Univ. Lib. of Ohio, Toledo Copyright 2006 Reed Business Information.

Product Details

ISBN-13:
9780822336990
Publisher:
Duke University Press Books
Publication date:
12/20/2005
Edition description:
New Edition
Pages:
224
Product dimensions:
6.10(w) x 9.20(h) x 0.60(d)

Related Subjects

Read an Excerpt

All about Your Eyes


By Sharon Fekrat, Jennifer S. Weizer, Stanley M. Coffman

Duke University Press

Copyright © 2006 Duke University Press
All rights reserved.
ISBN: 978-0-8223-9608-6



CHAPTER 1

Anatomy of the Eye and How It Works


Eyelids

RAVI CHANDRASHEKHAR, M.D., MSEE

The eyelids act as a protective covering for the eyeball while helping to keep its surface lubricated. Eyelashes help trap debris and prevent unwanted materials from entering the eye, and the lids themselves block excess light and foreign objects. The eyelids distribute the tear film evenly during blinking, and tiny glands on the edges of the eyelids produce oil which slows evaporation of the tear film and helps lubricate the eye's surface.

The eyelids are composed of several layers. The outermost layer is the skin, followed by a layer of muscle and more supportive tissue and finally by the innermost conjunctiva. The eyelid muscles help open and close the eyelids while giving them tone and shape. The conjunctiva on the inside of the eyelids is continuous with the conjunctiva on the surface of the eyeball.


Conjunctiva

RAVI CHANDRASHEKHAR, M.D., MSEE

The conjunctiva is a thin, transparent mucous membrane that covers three parts of the eye. It lines the inner surfaces of the upper and lower eyelids. It helps form a barrier inside the eyelids that separates the front half of the eyeball from the back half (this space is called the fornix). Finally, the conjunctiva becomes even thinner and continues over the front surface of the eyeball up to the edge of the cornea known as the limbus.

The conjunctiva serves as the outer protective surface of the eyeball, and the conjunctiva that lines the eyelids provides a smooth interface with the conjunctiva on the surface of the eyeball to make blinking and eye movements comfortable. Blood vessels in the conjunctiva help nourish the eye as well.

Although the conjunctiva is normally transparent, blood or inflammation can cause it to appear red or pink (as in subconjunctival hemorrhage or conjunctivitis).


Sclera

RAVI CHANDRASHEKHAR, M.D., MSEE

The sclera is the tough, white, outer layer of the eyeball. It begins at the edge of the cornea, or limbus, and surrounds the eyeball until it reaches the optic nerve in the back of the eye. The whiteness of the sclera gives the eye its white appearance outside the cornea, although the sclera is covered with clear conjunctiva in the front of the eye. In the back of the eye, the sclera lies just outside the choroid layer. The sclera is made of tightly woven interlocking fibers which protect the eyeball from injury and help it to hold its spherical shape.

Eye movement is controlled by six muscles that attach at various locations on the sclera. By pulling on the sclera, the muscles cause the eye to move in the desired direction. The sclera also contains tiny blood vessels which provide its nourishment.


Cornea

RAVI CHANDRASHEKHAR, M.D., MSEE

The cornea is the clear, round, central window in the front of the eyeball which light travels through to enter the eye. It is made up of five curved, transparent tissue layers and measures about 12 millimeters in diameter. Unlike other parts of the eye the cornea does not have a blood supply, but it does contain tiny nerves which make the cornea very sensitive to pain when touched or scratched.

The purposes of the cornea include protecting the eye, allowing light to enter the eye (hence the cornea is clear), and bending and refracting the light so that images can focus on the retina and travel to the brain, allowing us to see. Alterations in the normal, curved shape of the cornea can cause astigmatism, and changes in the cornea's shape also contribute to Nearsightedness and Farsightedness.


Iris

RAVI CHANDRASHEKHAR, M.D., MSEE

The iris is the colored, circular part of the eye that forms the pupil in its center. Irises range in color from blue to green to brown, depending on how much melanin, or pigment, they contain. A person with a brown iris has more melanin-containing cells in the iris than a person with a blue iris.

The iris divides the front part of the eye into two chambers. Eye structures in front of the iris are part of the anterior chamber, while structures behind the iris are part of the posterior chamber. The iris itself is made of muscles and tissues that adjust the size of the pupil so that the appropriate amount of light can travel though the pupil to form an image on the retina. This mechanism is similar to that of a camera, in which the amount of light to which the film is exposed is determined by the aperture of the lens.

The iris contains two sets of muscles. One set of muscles dilates the pupil so that more light can pass through to the retina. The other set of muscles constricts the pupil to let less light through. The body's central nervous system controls these muscle systems to let in the appropriate amount of light.

At the outer edge of the iris is the ciliary body, which is composed of irislike tissue. The zonules that support the lens insert into the ciliary body for support. The ciliary body contains muscles which contract and relax as the lens accommodates for near vision.


Pupil

RAVI CHANDRASHEKHAR, M.D., MSEE

The pupil is not an actual physical structure; rather, it is defined as the dark-appearing round space in the middle of the iris. Light passes through the pupil to reach the retina and form an image. Iris muscles control the size and shape of the pupil so that the proper amount of light reaches the retina. A larger pupil lets more light pass through the eye, which is useful in dim light, while a smaller pupil lets less light reach the retina, such as in bright sunlight.

The average diameter of the pupil is approximately 3 millimeters. Because the size of the pupil is regulated by the brain, checking the pupils' reaction to light is a basic test of brain function.


Chambers

RAVI CHANDRASHEKHAR, M.D., MSEE

The space inside the front part of the eyeball is divided into two main areas, or chambers. The front, or anterior, chamber is the space between the cornea and the front of the iris. The back, or posterior, chamber is between the back of the iris and the front of the vitreous gel. The posterior chamber surrounds the front of the lens.

The anterior chamber is filled with aqueous humor, a clear fluid produced by the eye to nourish itself. The aqueous humor normally drains out through the anterior chamber angle, which is at the edges of where the cornea meets the iris. This balance between production and drainage of aqueous humor helps to maintain healthy eye pressure.


Lens

RAVI CHANDRASHEKHAR, M.D., MSEE

The purpose of the lens is to refract, or bend, light so that an image can form on the retina for the brain to "see." The cornea performs about 70% of the necessary bending of light rays, while the lens performs the other 30%. The lens is shaped like a lentil and is located behind the iris, where it is suspended in its own clear capsular bag by fibers called zonules. The lens is made of proteins that form a crystal-like structure, resulting in a clear lens that allows light to pass through it. As a person ages, the proteins in the lens continue to grow, which makes the lens larger, more cloudy, and yellowish-brown. This normal aging is called a Cataract.

When a person looks at an object up close, the zonules change their tension on the lens, causing it to change its shape slightly. This response is called accommodation. As the lens ages and becomes thicker, it cannot change its shape as easily, and near objects become more difficult to focus on without the help of reading glasses.


Vitreous

RAVI CHANDRASHEKHAR, M.D., MSEE

The vitreous, or vitreous humor, is a transparent, gel-like substance in the vitreous cavity in the back of the eyeball. The vitreous occupies about 80% of the volume of the eyeball and helps the eye to maintain its spherical shape. The vitreous is composed of 99% water and 1% protein. It is attached to the retina at several points.

The vitreous gel becomes more liquid as a person ages. As it liquefies, the vitreous moves more freely inside the eye and its attachments to the retina can break free. This causes a posterior vitreous detachment, which is a normal aging change but can also occasionally lead to a retinal break or retinal detachment. The loose vitreous gel that moves inside the eye can cause floaters.


Retina

RAVI CHANDRASHEKHAR, M.D., MSEE

The retina is a thin layer of complex nerve tissue that lines the inside back wall of the eyeball. It is located between the vitreous and the choroid. The front edge of the retina is located at the ora serrata, just behind the ciliary body, and the back edge is at the border of the optic nerve. The retina contains its own blood vessels to provide itself with nutrients and oxygen. The small central area of the retina which is responsible for detailed central vision is called the macula.

The retina is composed often cell layers, all of which work together to receive images made of light rays, transfer those images into electrical signals, and send the signals to the brain to be "seen." Two types of specialized retinal cells, called rod and cone photoreceptors, play an especially important role in this visual process. These rods and cones actually change the incoming light rays from a visual image into electrical signals. The rods process black-and-white vision, while the cones process color vision. The electrical signals they produce travel through specialized nerve cells in the retina, which all come together to form the optic nerve. Because the macula is responsible for detailed color vision, there are more cone photoreceptors here than in the surrounding, or peripheral, retina.


Retinal Pigment Epithelium and Bruch's Membrane

RAVI CHANDRASHEKHAR, M.D., MSEE

Two important tissue layers that line the inside of the eyeball separate the retina from the choroid. The retinal pigment epithelium lies directly beneath the retina. It is made of a single layer of cells that provide nutrients to the overlying rod and cone photoreceptors in the retina and keep them functioning properly. Under the retinal pigment epithelium is Bruch's membrane. The purpose of this tissue layer is to separate the retina and retinal pigment epithelium from the choroid underneath. Because the choroid contains its own specialized blood vessels, Bruch's membrane keeps these vessels separated from the retina to allow it to function normally. In age-related macular degeneration, for example, cracks in Bruch's membrane occur, allowing choroidal vessels to grow underneath the retina and cause vision loss.


Choroid

RAVI CHANDRASHEKHAR, M.D., MSEE

The choroid is a layer of pigmented vascular tissue found between the retina and the sclera. It contains many blood vessels which supply the eye and retina with necessary nutrients and oxygen. The choroid, ciliary body, and iris together are known collectively as the Uvea, since they are all connected and composed of similar tissue. Besides containing blood vessels for the eye, the uvea is pigmented to absorb excess light as it enters the eye.


Optic Nerve

RAVI CHANDRASHEKHAR, M.D., MSEE

The optic nerve carries electrical signals from the retina toward the part of the brain known as the visual cortex. Nerve fibers from the retina come together in a bundle to form the optic nerve, which is connected to the brain. The fibers run through the brain, eventually reaching the back area, where the visual cortex is located.

The optic nerve contains the central retinal artery and central retinal vein that run to and from the eyeball to provide much of its blood supply and return. The optic nerve is surrounded by the same layers of tissue that surround the rest of the brain, making the optic nerve truly part of the brain. The back end of the optic nerve connects to the optic chiasm in the brain, which is a structure where both optic nerves (one from each eye) are joined.

The front end of the optic nerve, which is at the back of the eyeball, can be seen during a dilated eye examination. Your eye doctor examines the optic nerve here to look for signs of glaucoma, optic nerve swelling, or other optic nerve diseases.

The optic nerve can be thought of as the cable that carries information from the eye to the brain, where that information can be processed into an image that is "seen." Any damage to the optic nerve can disrupt this flow of information and lead to vision problems. Damage to the optic nerve can be permanent. A neuro-ophthalmologist specializes in diseases of the optic nerve.


Orbit

RAVI CHANDRASHEKHAR, M.D., MSEE

The eyeball sits in a cavity in the head known as the orbit, or eye socket. The orbit is shaped like a pyramid with four walls lying on its side, its tip pointed toward the brain. The walls of the orbit are made of seven bones which protect the eyeball from injury, and much of the orbit behind the eyeball is filled with fat to provide a supportive cushion for the eye. Also in the orbit are blood vessels, eye muscles which move the eyeball, the lacrimal gland which produces tears to lubricate the eye, and nerves involved in vision, sensation, and eye movements.

At the back of the orbit is a small opening known as the optic canal, through which the optic nerve passes on its way to the brain. Other blood vessels and nerves connected to the brain also enter the orbit through this opening.


Pathways from the Eye to the Brain

RAVI CHANDRASHEKHAR, M.D., MSEE

In order for us to see, light must travel through the eye all the way back to the brain, where it is processed so we can "see" an image. First, light rays strike the cornea, where they are bent, or refracted. These light rays then pass through the anterior chamber and the pupil. Next they reach the lens, where they are refracted even further. The light then passes through the clear vitreous and hits the retina in the back of the eye, where light is converted into electrical signals. These electrical signals travel through the optic nerve to the optic chiasm, where the information from both eyes is combined.

In the brain the optic chiasm splits into two pathways known as the optic tracts, one on each side of the brain. The optic tracts continue to travel back toward the visual cortex of the brain, spreading out into the optic radiations. These optic radiations finally reach the visual cortex at the back of the head, where the brain processes the electrical signals into images. With so many nerve fibers traveling through the brain, a large part of the brain's area is involved in the visual system. Any disruption anywhere along the visual pathway can lead to vision loss.

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How the Eye Works

CAROL J. ZIEL, M.D.

As you can see by reading about the anatomy of the eye, there are many structures that are necessary to give us vision. The human visual system is designed to give us depth perception, which means that we can tell which objects are in front of or behind other objects. Depth perception is useful for doing simple tasks, such as pouring a cup of coffee or driving a car, and is even more important in tasks that require detailed eye-hand coordination, such as performing surgery.

How exactly are the eyes designed to give us depth perception? First, both eyes must have normal or near normal vision to work together. Glasses or contact lenses may be needed to obtain normal, or 20/20, vision. Then, the eyes must be aligned in the skull so that they are facing in the same direction and are close enough together that each eye's peripheral vision, or side vision, overlaps considerably with that of the other. If we cover one eye and then the other when looking at an object, we can tell that each eye is seeing the same object just a little differently. As we cover and uncover each eye, it is as if the object moves a little to the right or to the left. Therefore, each eye receives a slightly different image that is sent to the brain for processing.

The ability of the brain to process or blend these two similar images is called fusion. The brain must be able to maintain the blending of these images into one image as the eyes move together in various directions. High-level fusion develops completely during childhood, usually between the ages of 5 and 9.

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CHAPTER 2

Preventive Eye Care


Recommended Schedule for Eye Exams

CAROL J. ZIEL, M.D.

Eye exams are recommended throughout life to ensure the proper development and maintenance of good vision. These exams allow the eye doctor to discover any problems that can be corrected to prevent or reverse vision loss.

Vision screenings are performed on newborns and babies by eye doctors or pediatricians to ensure that there are no obstructions in the visual pathway (such as congenital cataracts), that the eyes are looking straight ahead and are aligned together, and that each eye is seeing well independently. Vision screenings should be performed every two years unless problems arise sooner. At the age of 5 or when the child begins school, a formal eye exam is recommended so that the visual acuity, or level of vision, can be measured accurately.

Once the vision has developed completely in adults, a full eye exam every ten years between the ages of 20 and 39 may be sufficient unless a patient has a known eye problem or risk factors for eye disease. During those years, eye evaluations for glasses or contact lenses may be necessary. After 40 to 45 years of age, a full, comprehensive eye exam, including dilation, should be done every two years to check for eye problems such as glaucoma, age-related macular degeneration, and cataract, as these diseases increase with age. People with known eye problems may need to be examined more often. Patients with diabetes should be examined at least yearly and sometimes more often, depending on the degree of diabetic eye disease.

http://www.aao.org http://www.opted.org http://www.aoa.org http://www.oaa.org


(Continues...)

Excerpted from All about Your Eyes by Sharon Fekrat, Jennifer S. Weizer, Stanley M. Coffman. Copyright © 2006 Duke University Press. Excerpted by permission of Duke University Press.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

Meet the Author

Sharon Fekrat, M.D., FACS, is a practicing vitreoretinal surgeon and an associate professor in the Department of Ophthalmology at Duke University. She is president of the North Carolina Society of Eye Physicians and Surgeons.

Jennifer S. Weizer, M.D. is a clinical assistant professor in the Kellogg Eye Center at the University of Michigan.

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