What are Cataracts?
How the Aging Eye Works
While the comparison of the eye to the camera allows us to understand how the eye works at a basic level, the eye is actually far more sophisticated than a camera. And many of these complicated functions change as we age.
Here we concentrate on those parts of the eye that undergo the types of changes that are important for us to be aware of so that we can then understand cataracts and cataract treatment.
For More Information on the Aging Eye
Order a copy of the Harvard Medical School's "Special Health Report on The Aging Eye."
The eyeball sits in the skull within the orbit, which is surrounded by a protective layer of fat, fibrous tissue, and muscle. The wall of the eyeball is composed of three distinct layers of tissue.
The outer layer is composed of collagen and includes both the sclera and the cornea. Because the cornea is the first part of your eye that light passes through, it plays an important role in the ability of your eye to focus light on the retina. Your doctor will take variations in the shape of your cornea, such as myopia (also called nearsightedness), hyperopia (also called farsightedness), and astigmatism, into consideration in developing an overall course of treatment for cataracts.
The middle layer is called the uveal tract and is made up of the pigmented iris, the ciliary body, and the choroid. The iris is a circular curtain of muscle fibers that automatically contracts and expands to let the optimal amount of light into the eye where it hits the lens.
The expanding and contracting area where light enters is called the pupil. As we age, the unkindly named condition senile miosis can make the resting size of the pupil smaller, reducing the amount of light that can enter and hit the lens.
The lens is a transparent, flexible, bi-convex (lentil-shaped) structure made of crystallin, a water-soluble structural protein. In age-related cataracts, a cataract occurs when these proteins coagulate or clump together, resulting in a lens that is thicker, less transparent, and less flexible.
Did You Know?
A cataract cannot be removed from a lens. Rather, the lens itself must be removed and replaced with a new artificial lens. This artificial lens is called an intraocular lens, or IOL. Learn more about how different types of cataracts affect different parts of the lens.
The lens sits in a capsular bag which is connected to ligaments called zonules, which are in turn, connected to the muscles in the ciliary body. These muscles and zonules work together to flex the bag with the lens inside to allow it to focus light on the retina.
This flexing is called accommodation. As the natural lens of the eye ages, it often hardens and is less able to accommodate. This hardening of the lens, which can occur independently of cataracts, is often accompanied by a loss of flexibility in the surrounding muscles. This loss of flexibility is commonly called presbyopia. But because presbyopia is a function of aging – most people begin experiencing signs of presbyopia in their early to mid 40s – many people with cataracts also have presbyopia. In recent years, multifocal intraocular lenses have been developed to correct both cataracts and presbyopia.
In the innermost layer of the eye is the retina, a mass of fibers and specialized cells called cones and rods. The cones and rods of the eye are made up of chemicals that react to different wavelengths of light. The rods are located primarily at the periphery of the retina and provide our peripheral vision. The cones, which are concentrated in the center of the retina, or the macula, perceive color and are responsible for fine detail in the center of our vision. When macular degeneration occurs, our central vision suffers. If you suffer from macular degeneration as well as cataracts, your doctor may recommend that your receive cataract surgery anyway to make it easier to treat the damaged retina.
Learn more about the types of cataracts.
- (1) Much of this content has been adapted from "The Aging Eye: A Special Health Report from Harvard Medical School," Ed. Fine, Laura C. M.D and Heier, Jeffrey S. M.D., copyright 2006, Harvard Health Publications, Boston, MA.
- Site Index
- Contact Us
- Accessibility Statement
- Privacy Policy
- Terms & Conditions
| Cataract Information | Cataract Treatment | Cataract Operations |
Copyright © 2010 Alcon, Inc., a global company based in Hünenberg, Switzerland. The information on this site is intended for U.S. audiences and is not to be interpreted as a substitute for medical advice from your doctor.
