Anatomy of an Eye
At the front of each eye lies the cornea, a rounded bulge that allows light inside. That light passes through the pupil, a transparent space in the center of the colored iris. Behind the pupil is the lens, which is connected to the zonules (ligaments that tighten and slacken to focus). Light goes through the lens and hits the retina, the tissue at the back of the eye, which sends a message through the optic nerve to the brain, telling it what you’re looking at.
From Birth Through Your 30s
When you are born, the lenses inside your eyes are generally crystal clear and flexible, and the zonules connected to them are strong. With age, the lenses become less flexible, and the zonules are not as effective. Your eye shape, which is genetically determined, may mean that you need corrective lenses. If your eyeballs are too long, you’re nearsighted. If they are somewhat short, you’re farsighted. Whenever you notice a change in your vision, schedule an appointment with an ophthalmologist or an optometrist.
In Your 40s
“This decade is when we begin to lose our ability to focus up close, which is called presbyopia,” says Andrew Iwach, M.D., a spokesperson for the American Academy of Ophthalmology and the executive director of the Glaucoma Center of San Francisco. Thank those thicker, harder lenses and weaker zonules. The remedy? Reading glasses. (Don’t feel bad―everyone needs them eventually.) How quickly you develop presbyopia depends on where your vision started. If you have always had perfect eyesight, you’ll probably need reading glasses in your early 40s. Nearsighted people have an edge and often won’t notice a change until their late 40s, says Jill Koury, an assistant professor of ophthalmology at the Duke University Eye Center, in Durham, North Carolina. If you’re farsighted, you’ll probably need those specs in your late 30s. This is also the time to schedule a comprehensive baseline eye exam (aim to go in at age 40 if you haven’t already). Among other things, a doctor will test the pressure inside your eyes and look at the optic nerves to be sure they are intact.
In Your 50s and Beyond
The lenses continue to harden, and you may find you need stronger corrective lenses or even bifocals, which are lenses that have two prescriptions built into them (they are now available in contact lenses, too). You are also at greater risk of developing the following eye diseases.
- Cataracts. These form when the lenses of the eyes become cloudy. More than 20 million Americans have cataracts, and everyone, if he or she lives long enough, will develop them. Age is the number one culprit, says Carol L. Karp, a professor of clinical ophthalmology at the Bascom Palmer Eye Institute, at the University of Miami Miller School of Medicine, in Florida. Smoking and sun exposure are also contributors.
- Glaucoma. This disease affects more than 2 million people in the United States and is typically associated with pressure building up in the eyes, resulting in damage to the optic nerves, says Emily Bedrick Graubart, an assistant professor of ophthalmology at the Emory Eye Center and the Emory University School of Medicine, in Atlanta. Glaucoma causes peripheral-vision loss and can eventually lead to blindness. It’s one of the most common reasons worldwide why adults lose their sight.
- Macular degeneration. If the macula (a part of the retina) deteriorates due to heredity or environmental factors, the central line of sight becomes impaired. Blurred vision is often the first sign. Macular degeneration affects almost 2 million people in the United States and is the leading cause of vision loss in Caucasians over the age of 65. Ultraviolet (UV) light can speed its development, as can smoking.
Answers to the questions that patients commonly ask their doctors.
Q. Whom should I see for my exam, an ophthalmologist or an optometrist?
A. Either. An ophthalmologist is a doctor of medicine (M.D.), which means he or she went to medical school and had an internship and a residency in ophthalmology. An optometrist is a doctor of optometry (O.D.) and has completed four years of optometry school. Both can give comprehensive examinations and prescribe glasses and contacts. But only an ophthalmologist can perform surgery.
Q. How often should I have my eyes examined?
A. According to Dori Carlson, an optometrist and a spokesperson for the American Optometric Association, a child should have his first screening, generally done by a pediatrician, anywhere from birth to age one. A second screening should be done at age three and another before the child starts school. Carlson suggests yearly exams after that, unless a doctor tells you otherwise. Most important, experts recommend having a comprehensive examination at age 40. If you start to notice changes in your vision, see a doctor, regardless of your age.
Q. Do I need to have my eyes dilated during an exam?
A. Probably. It’s the most common way a doctor can see deep inside the eyes to ensure that the optic nerves are healthy and to check the retinas. Schedule an appointment late in the day, when outdoor light isn’t too bright and you can avoid reading and computer work afterward, says Carlson. However, some ophthalmologists use a machine that lets them see into the eye without dilating.
Q. Why do my eyes start stinging when I’m tired?
A. The most likely culprit is dryness. When your eyes have been open for many hours, their surfaces dry out. And if you’ve been watching TV or using a computer, the problem can occur even more quickly, since when you look intently at something, you blink less and so lubricate your eyes less. Also, as you age, your ability to produce tears decreases. When your eyes are dry, they can’t flush irritants from the surfaces, so they may sting or feel scratchy. The solution: Use preservative-free artificial tears when you feel that burning sensation. (They’re safe to use with contacts.)
Q. Sometimes I see little squiggles in my vision. What are these?
A. They’re called floaters. Each eye is filled with a jellylike substance called the vitreous humor. It’s crystal clear and firm when you are young, but as you age, it liquefies. Floaters are simply little clumps of this jelly that cast shadows on the retina. They can be perfectly normal, says Koury, and you should worry only if they increase dramatically in number or if you see flashes of light, too.
Q. Can two brown-eyed parents have a blue-eyed child?
A. Yes. Eye color is determined by the amount of melanin in the irises. A bunch of genes control how much melanin develops. “Because eye color isn’t dependent on one gene, it’s possible for two people with brown eyes to have a baby with blue eyes or for two parents with blue eyes to have a brown-eyed child,” says Graubart. Many babies are born with blue eyes, as the genes responsible for iris pigmentation haven’t yet kicked in. If the genes end up telling the irises to produce more melanin, the eyes darken.