Alan Stern, M.D. [August 20 2010]
It sounds counterintuitive – pushing a newspaper or book farther away so you can read it better.
But if you're over 40 you might find yourself doing just that – with the newspaper, books, labels and anything else requiring you to focus on something close. The cause might be presbyopia, an age-related eye condition that affects nearly everyone.
Presbyopia is not a disease. It's a perfectly natural part of aging, but it can be a little annoying. Those who have it have trouble focusing on things at a normal reading distance (considered to be about 14 inches from the eyes). Other symptoms may include eye fatigue and headaches while doing close work, like sewing or tying flies for fishing.
To understand what causes presbyopia, you need a basic understanding of how we see. Vision occurs when your eyes process light rays that are reflected off objects you're looking at. The cornea, the clear, domed structure at the front of the eye, helps bend the light rays, which then pass through the pupil to the lens. With help from muscles surrounding it, the flexible lens actually changes shape to further bend the light rays and focus them on the retina in the back of the eye.
Presbyopia occurs when the lens loses its flexibility and is no longer able to bend the light rays as effectively. While this change might seem sudden to you, it actually takes years to occur. Symptoms usually become noticeable around the early to mid-40s and continue to worsen until around age 60. (In some cases, presbyopia can appear before age 40 as a result of certain diseases or medications. If you experience premature presbyopia, see your doctor.)
While presbyopia can't be prevented, it's usually easily corrected. People who don't already need glasses to correct near- or farsightedness may be able to use non-prescription “reading glasses” available in most pharmacies. Or, they can get a prescription for glasses they'll wear only while reading or doing close work.
For those who already wear glasses, bifocals or trifocals may be good options. These eyeglasses combine different prescriptions into one lens and come with visible lines or without (called progressive lenses). Looking through bifocals at eye level will correct your distance vision. Looking down through the lower part of the lens corrects vision for reading and close work. Trifocals correct vision for close work, middle-distance vision — such as for computer screens — and distance vision.
Contact lens wearers can get bifocal contact lenses or monovision lenses, in which one lens corrects distance vision and the other closer vision. There are also modified monovision contact lenses. With this option, a bifocal lens is worn in one eye, and a distance lens in the other. Both eyes are used for distance vision and one for reading. While it sounds strange, the brain usually adjusts, so you'll instinctively use the correct eye for whatever you're viewing.
Presbyopia can also be reduced through refractive surgery to reshape the eye's cornea. It's equivalent to wearing monovision contact lenses, so if you're considering refractive surgery, it's best to try monovision contact lenses first to be sure you can adjust.
Your ophthalmologist can talk to you about the best options for correcting presbyopia and help you see better, no matter what your age.
Alan Stern, M.D., is head of the Division of Ophthalmology at The Hospital of Central Connecticut.