As we age, the lens of the eye becomes increasingly inflexible, making it harder to focus clearly on near objects. This is called presbyopia. No one knows exactly what causes the lens to become inflexible, but it happens to everyone as a natural part of aging.
In order for us to see images clearly, light rays enter the eye, where the lens bends and focuses the rays on the retina. The lens changes shape to allow the eye to focus on objects at different distances. Beginning early in life -- perhaps as early as age 10 -- our lenses gradually stiffen and begin to lose the ability to change shape. By the time we are in our 40s, the lens has trouble focusing up close, and we begin to experience blurred vision when we try to do tasks that require up-close focus, such as reading or needlework. The lens continues to stiffen until about age 65, when nearly all its flexibility has been lost.
Presbyopia eventually affects everyone, even people who are already farsighted (hyperopic) or nearsighted (myopic). Because people who are farsighted already need to work when focusing on near objects, they may experience presbyopia a little earlier in life. People who are nearsighted will still experience presbyopia when wearing their corrective glasses or contact lenses for distance. However, for looking at objects or letters closer to them, they will likely be able to see quite clearly when they take off their glasses. This is where the term "nearsighted" comes from.
Presbyopia causes the following symptoms:
- Words appear blurred at a reading distance that used to be comfortable.
- Reading material or other objects must be held farther away from your eyes to gain clarity or see details.
- Brighter light is needed to see clearly (bright light constricts the pupils, which changes the focus of the light on the retina).
- You have difficulty reading late at night, or when you are tired or stressed.
- Your eyes become uncomfortable, or you become tired or drowsy when doing close work because of the strain of eye muscles working to change the lens shape.
- You may have headaches as a result of muscle tension.
Many people over age 40 diagnose presbyopia themselves based on their inability to read clearly at a distance that used to be natural and comfortable. Because the condition comes on gradually over many years, most people don't notice small vision changes and delay seeking professional help until the focusing problems interfere with daily life. Many optometrists joke that patients seek help only when their arms become "too short," unable to hold printed pages far enough away to see clearly.
Presbyopia can be diagnosed by an optometrist, ophthalmologist or physician, who will take a complete medical history to determine the extent of your vision problem. He or she will test your vision by having you read text at a distance that is typically comfortable to you. If the doctor diagnoses presbyopia, he or she will do a test to determine the extent of the focusing problem and the appropriate lens prescription. In this test, the doctor has you look through corrective lenses, and continues to increase the magnification power until the words on the page are clear to you and you are comfortable reading.
Presbyopia cannot be reversed and gets worse as we get older. Vision changes stop around age 65. The only exception is that which occurs when people develop a type of cataract that causes them to be myopic (nearsighted). Such cataracts cause "second sight." Reading vision returns but of course distance vision becomes blurred.
Nothing can be done to prevent presbyopia. It is an inevitable part of aging. However, people who do a lot of close visual work, such as working with a computer or intensive reading, may develop presbyopia earlier than others. If you do close work, take a 10-minute break every 1 to 2 hours to relieve strain on the eyes. Allow your eyes to focus on objects at a middle or long distance away to give your eyes a rest from close focusing. Be sure to use bright lighting when reading to help your eyes focus.
Presbyopia can be treated with corrective lenses. Glasses are the simplest way to regain your ability to see close objects clearly. If you already wear corrective lenses for nearsightedness or farsightedness you may need two sets of glasses -- one for distance vision and one for close vision -- or glasses with bifocal lenses, in which the upper portion of the glass corrects for distance and the lower portion for near vision. Your optometrist or vision professional can order the appropriate prescriptions.
If you don't already wear corrective lenses or you wear contact lenses, you may choose to wear reading glasses only when necessary to magnify up-close objects. The strength of reading glasses is categorized in increments of .25. Glasses with +.50 have a minimal amount of correction -- only two steps. Standard lenses are available up to +6.00 (24 steps of reading correction), but typically range from +1.00 (four steps) to +2.50 (10 steps). Your vision professional can tell you what amount of correction is best for your eyes.
Standard, inexpensive reading glasses are available in most drugstores, supermarkets and office supply stores. They are rated on the same vision correction scale, so if you know the amount of correction you need, you can purchase the right pair for you. If you don't know how much correction you need, test the glasses in the store by trying to read text at a comfortable distance using different magnification strengths. The one that allows you to read most clearly is the right power for you.
Standard, off-the-rack reading glasses may not be right for everyone. Many people need different amounts of correction in each eye, and therefore require custom glasses. Also, custom glasses usually are made of better materials and are shaped to allow your eyes to focus properly across the full range of the lens.
Because presbyopia continues to get worse as we age, the magnification you need may change over time.
Contact lenses also can be used to treat presbyopia, although many people find it difficult to adjust to them. Bifocal contact lenses can be made, or you can get monovision lenses, in which one eye has a contact lens with a prescription for distance vision, and the other eye has a contact lens for up-close vision.
Although there is no harm in delaying treatment for presbyopia, optometrists recommend seeing a professional whenever you have blurred vision because this can indicate other vision or health problems. For example, cataracts also can cause blurred vision, and diabetes, multiple sclerosis, vascular disease and other diseases can affect vision. If your vision suddenly blurs, or if you have eye pain or double vision, see black spots or light flashes or have other visual problems, see your doctor immediately.
The condition will continue to get worse, then stabilize. With proper corrective glasses or contact lenses, you'll still be able to read and do other close work as well as ever.
American Optometric Association
243 North Lindbergh Blvd.
St. Louis, MO 63141
National Eye Institute
2020 Vision Place
Bethesda, MD 20892-3655