Uday Devgan, MD, is chief of ophthalmology at Olive View University of California–Los Angeles (UCLA) Medical Center and associate clinical professor at the Jules Stein Eye Institute at the UCLA School of Medicine. He is the author of more than 100 books, technical articles, and scientific papers on ocular surgical techniques. He lives in Los Angeles. Robert Maloney, M.D., M.A., F.A.C.S., a Rhodes Scholar, trained at Oxford University, Harvard University, and Johns Hopkins Hospital. He is founder and director of the U.C.L.A. Laser Refractive Center at the Jules Stein Eye Institute, and is Director of the Maloney Vision Institute in Westwood, California.

Cataract Surgery

A Patient’s Guide to Cataract Treatment

By Robert K. Maloney, Mark Erickson, Jack Kusler

Addicus Books, Inc.

Copyright © 2008 Robert K. Maloney, MD, Inc.
All rights reserved.
ISBN: 978-1-886039-94-0

Contents

Acknowledgments,
Introduction,
1 The Human Eye and How It Works,
2 What Is a Cataract?,
3 Signs and Symptoms,
4 Causes and Risk Factors,
5 Your Eye Examination,
6 Planning for Cataract Surgery,
7 Your Cataract Procedure,
8 Risks and Side Effects of Cataract Surgery,
9 The Future of Cataract Treatment,
Resources,
Glossary,
Index,
About the Author,

CHAPTER 1

The Human Eye and How It Works

To understand how cataracts cause blurry vision, you’ll probably find it helpful to know something about the structure of the eye and how it works. The eye is a complex organ that performs many complicated functions in a very short time — in the blink of an eye, you might say.

Anatomy of the Eye

If you could examine an entire human eye, you’d see a sphere about an inch in diameter — the size of a large gumball. The eyeball itself is really three thin layers surrounding a fluid-filled center.

Sclera

The outside layer is the “white of the eye,” called the sclera. It is the tough, opaque tissue that serves as the eye’s protective outer coat. Six tiny muscles connect to it around the eye and control the eye’s movements. The optic nerve is attached to the sclera at the very back of the eye.

Cornea

Curving out from the sclera, the clear cornea is the “front window” of the eye. The cornea is amazingly strong and protective against dust and germs. Packed with nerve fibers, it is also quite sensitive to pain. This pain sensitivity is one of the cornea’s protective qualities; the pain is a signal that something is trying to invade the eye.

Iris

Under the sclera is another thin layer, which consists of the iris — the eye’s visible colored ring; when we say that someone’s eyes are blue, brown, or green, we are talking about the color of the iris. Besides being an interesting and expressive feature of the face, the iris is essential to clear vision. It surrounds the round, black pupil — along with muscle fibers and blood vessels.

Lens

The muscle fibers hold the lens of the eye in place and allow it to change its shape so that it can focus on objects at different distances. Located behind the iris and the pupil, the lens is about two-thirds water and one-third protein fibers. There are three distinct layers in the lens, sometimes compared to the layers of a peach:

The capsule (the peach “skin”) is a thin, clear membrane that forms the outside layer of the lens.

The cortex (comparable to the peach “flesh”) is the soft, clear material just beneath the capsule.

The nucleus (the “pit” of the peach) is the firm center, or core, of the lens.

Retina

The blood vessels, located toward the back of the eye, feed essential nutrients to the retina, a smooth, thin layer of nerve tissue at the back of the eye. When you are looking at an object, the retina is where the image comes into focus. Most of the retina contains specialized cells that convert the reflected light (the image) to signals your brain can interpret.

The macula is the focal point at the center of the retina. Within the macula are millions of lightsensitive nerve endings that act as photoreceptors.

The photoreceptors called rods are sensitive to brightness and allow us to see in dim light.

The photoreceptors called cones respond to the varying wavelengths of light that produce different colors.

The fovea centralis, in the center of the macula, is densely packed with cone cells. It is the fovea that gives your eye the ability to sharpen an image. The clearest vision — what we call” 20/20 vision’ — would be impossible without the fovea.

Another part of the retina, the retinal pigment epithelium, consists of dark tissue cells that absorb excess light and carry nutrients to, and waste products from, the retina.

Features that Protect the Eyes

The eyeballs are protected, in part, by their location — they are embedded in sockets, which are strongholds of bone, fat, and muscle. Other protective features of the eye are:

• Eyelashes, which protect your eyes from dust, contaminants, and other small particles

• Eyebrows, which trap liquids (such as perspiration) and particles that might otherwise find their way into your eyes

• Tears, which supply moisture that not only keeps your eyes from drying out but also contain substances that fight bacteria. If a foreign object gets into your eye, tear production increases to flush it out. When perspiration drips into your eyes, the high salt content makes your eyes sting, and the stinging stimulates tear production. The tears dilute the salty perspiration (or other liquid that might accidentally enter your eye) and cleanse the eye.

• Eyelids, which work like windshield wipers when you blink, to spread tears across the cornea. Blinking is usually automatic — you seldom have to remember to blink — but it is also a protective reflex that goes into action when your eyes perceive an object moving toward them or are assaulted by extremely bright light.

How Vision Occurs

Let’s say you’re looking at autumn leaves. Light reflects off the leaves and enters the eye through the cornea, then travels through several structures to the back of the eye, where the image reaches its sharpest focus. From there, the optic nerve carries the focused “leaves images” to the brain. Only then can you actually see the leaves.

Let’s take a closer look at this process. It might be helpful to think of seeing as four distinct processes, which are roughly similar to the way a camera processes an image.

1. Light Reflects Off an Object

When you’re admiring the beautiful orange and red foliage on a maple tree in autumn, you’re actually seeing the light reflecting off them — just as a photograph is an image of light reflecting off an object. If this were not the case, then you’d be able to see objects at night, or photograph them, just as well as in daylight.

2. Light Enters the Eye

As it reaches the eye, the form of energy that we call light first enters the clear, curved cornea. The curved surface of the cornea bends the incoming light so that the rays come together, like branches, instead of remaining parallel as they enter the eye. Thus the cornea does most of the focusing work of the eye.

After passing through the cornea, light is bathed in a thin layer of liquid, the aqueous humor, before it reaches the iris. The iris contracts or expands (dilates) around the pupil to regulate the amount of light allowed into the eye’s interior. Sophisticated cameras have light-regulating mechanisms that do much the same thing.

When you walk out of a dark movie theater into bright daylight, you’ve probably experienced that “blinding” sensation before the iris has time to contract, adjusting to the difference in light.

3. Light Is Focused in the Lens

The lens, by changing its shape, also contributes to the eye’s focusing work. The lens is round and usually somewhat flat. When you were younger, most likely your eye lenses were perfectly clear and quite flexible. Some eye specialists compare the lens to a small, clear gelcap with a thin but sturdy exterior. If you squeeze it in the middle, it gets thinner and flatter; if you squeeze the ends, it gets thicker and more rounded.

That’s basically what happens to the eye lens when you focus on objects at varying distances, except that the work of “squeezing,” or contracting, is done by muscles called ciliary muscles and the ligaments attached to them (zonules). These muscles and ligaments also hold the lens in place.

When you focus on something close up, the ciliary muscles contract, making the lens thicker and rounder. As your focus moves outward to more-distant objects, the muscles relax and the lens becomes thinner and flatter. Thus, the lens projects a clear image onto the retina, at the back of the eye, whether the source of the image is near or far, or somewhere between.

This shape-changing adjustment to distance is called accommodation. Although the cornea does the initial focusing, it is the lens and its accommodation ability that allow you to focus well at different distances.

Once light passes through the lens, it enters the spacious cavity that occupies about two-thirds of the eye. This cavity is filled with a clear gel called vitreous, or vitreous humor, which helps the eye maintain its round shape.

4. Light Signals Are Interpreted by the Brain

Finally, the light reaches its destination — the retina, which receives images in much the same way that camera film does. After the retina’s specialized cells, rods, and cones have converted the image to signals that the brain can understand, the signals are finally carried to the brain through the nerve bundle at the back of eye — the optic nerve, which consists of millions of nerve fibers. The brain receives and interprets the signals, and it is at that point that we actually see.

The eye is sometimes described as an extension of the brain, and if there is severe damage to the optic nerve, the eye becomes useless. Vision occurs only when an image reaches the brain and is identified.

Eye-Structure Abnormalities

The process described above works best if the eye is a perfect sphere and the cornea is smooth and rounded. Often this isn’t the case. The eye might be shorter or longer from front to back than it is from top to bottom, or the cornea’s curvature might be slightly flattened.

Farsightedness and Nearsightedness

If your own eyes are shorter than normal from front to back, then you have hyperopia, or farsightedness, and you see distant objects more clearly than near ones. If the opposite is true — your eyes are too long from front to back — you have myopia, or nearsightedness, and you have trouble seeing distant objects.

Astigmatism

The cornea’s curvature should be rounded, like the side of a basketball. If, instead, it’s shaped more like the side of a football, it will produce two focal points instead of just one. This condition is called astigmatism and it causes blur and distortion, especially up close.

Cataracts and Lens Function

You can see how many structures and processes are important to the act of seeing. If just one structure is defective or one process doesn’t work properly, the eyesight — so important to most of us in almost everything we do — can be damaged. Like other parts of our bodies, our eyes don’t function as well when we age as they did when we were young.

Cataracts are the most common age-related eye defect. The next chapter will explain what cataracts are and how they interfere with the intricate function of the lens.

CHAPTER 2

What Is a Cataract?

If you’re in your mid-fifties or older, there’s a good chance that your eyes have started to develop cataracts. You can’t see them, you can’t feel them, and until they begin to seriously affect your vision you don’t really need to do anything about them except continue to take good care of your eyes. That means having regular eye exams and protecting your eyes — from injury, from the sun’s ultraviolet (UV) rays, and from irritants such as dust and wind.

A cataract is a clouding of the natural lens inside the eye. The clouded areas are often called opacities because they are opaque, meaning they are not clear, and light cannot pass through. The lens must be crystal clear to do its focusing job, so the areas of opacity interfere with good vision.

What Causes Cataracts?

Protein fibers in the lens, called crystallines, are precisely arranged in thousands of layers. Usually because of aging, the proteins deteriorate or become “disarranged.” Some scientists believe that these fragmented proteins cause the densities, or “clumps,” that cloud areas of the lens. These dense areas are cataracts, and as they become larger they cause noticeable vision loss.

People sometimes confuse cataracts with an unrelated lens condition, presbyopia — a stiffening of the lens also caused by aging. Throughout life, the lens continues to manufacture new layers of cells, and the accumulation of layers makes the lens less pliable. As the lens loses its flexibility, it also loses the ability to accommodate as well as it once could. At about age forty-five, most people — even those who have had excellent vision — find that “their arms are too short.” They have to hold books and magazines farther from their eyes in order to focus on the print. If presbyopia is your only vision problem, you can probably solve it with inexpensive reading glasses.

Types of Cataracts

You will usually see cataracts classified according to their location on the lens: nuclear, cortical, or subcapsular. A nuclear cataract is the most common and is the type most associated with aging, although older patients often have more than one type.

Nuclear Cataracts

A nuclear cataract, as the name suggests, is a clouding of the center of the lens, almost always due to aging. One of the early symptoms, oddly enough, is that your near vision will improve for a while. This improvement, referred to as second sight, is short-lived, however. As the cataract advances, the lens becomes yellow or even brown. Vision becomes dimmer and blurrier, and you’re likely to have trouble distinguishing colors. Glare might bother you, making it hard to drive at night. You may need stronger light for pursuits such as reading and needlework.

Cortical Cataracts

Many people develop cortical cataracts with age. These cataracts begin as whitish, wedge-shaped opaque areas on the outer edge of the lens cortex, near the capsule. Slowly, these opacities become streaks reaching inward to the center of the lens, like spokes on a wheel. When they reach the center, they block part of the light passing through the nucleus of the lens, and you will begin to have problems with focusing, distortion, and glare. Because both distance and near vision are impaired, you may require surgery at a comparatively early stage. If you have diabetes, you may be particularly susceptible to cortical cataracts.

Subcapsular Cataracts

When a subcapsular cataract begins at the back of the lens, which is most often the case, it’s called a posterior subcapsular cataract. It starts out as a grainlike opaque area under the lens capsule. Because posterior subcapsular cataracts are usually directly in the path of light on its way to the retina, you might have vision problems early on, particularly with glare and halos.

Anyone can have subcapsular cataracts in one or both eyes. People who are extremely nearsighted, who have diabetes, or who are taking high doses of steroids are particularly at risk.

How Common Are Cataracts?

Nearly everyone will eventually have cataracts. Estimates differ because not all who are affected seek treatment, but current research indicates that by age seventy-five at least 70 percent of Americans either have had cataract surgery or cannot see well because of cataracts. You’ll likely begin to notice cataract-related vision problems in your early to mid-sixties.

Cataract surgery is the most common surgical procedure in the United States. Some 3 million Americans have cataract surgery every year, often in an outpatient procedure that takes less than ten to fifteen minutes. The surgeon replaces the clouded natural lens with a clear synthetic lens through a tiny incision. These procedures nearly always succeed in greatly improving the patient’s vision, with almost no interruption in daily activities.

How Do Cataracts Affect the Eyes?

As explained earlier, all light entering the eye passes through the lens. Your lens must be clear for light to focus properly on the retina. Therefore, any clouding of the lens will affect your vision to some extent.

In most people, cataracts develop gradually and their eyesight may be adequate for several years before surgery is necessary. Other people experience more-rapid progression of cataracts, especially if several areas of the lens are affected. Cataracts that form directly behind the pupil are likely to cause problems sooner than cataracts closer to the edges of the lens.

(Continues…)Excerpted from Cataract Surgery by Robert K. Maloney, Mark Erickson, Jack Kusler. Copyright © 2008 Robert K. Maloney, MD, Inc.. Excerpted by permission of Addicus Books, Inc..
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.