Presbyopia
Presbyopia is the condition that causes loss of near vision as we get older. It usually occurs beginning at around age 40, when people experience blurred near vision when reading, sewing or working at the computer.
You can't escape presbyopia, even if you've never had a vision problem before. Even people who are nearsighted will notice that their near vision blurs when they wear their usual eyeglasses or contact lenses to correct distance vision.
Presbyopia Symptoms and Signs
When people develop presbyopia, they find they need to hold books, magazines, newspapers, menus and other reading materials at arm's length in order to focus properly. When they perform near work, such as embroidery or handwriting, they may develop headaches, eye strain or feel fatigued.
What Causes Presbyopia?
Presbyopia is caused by an age-related process. This differs from astigmatism, nearsightedness and farsightedness, which are related to the shape of the eyeball and caused by genetic and environmental factors. Presbyopia generally is believed to stem from a gradual thickening and loss of flexibility of the natural lens inside your eye.
These age-related changes occur within the proteins in the lens, making the lens harder and less elastic over time. Age-related changes also take place in the muscle fibers surrounding the lens. With less elasticity, the eye has a harder time focusing up close. Other, less popular theories exist as well.
Presbyopia Treatment: Eyewear
Eyeglasses with bifocal or progressive addition lensesare a common correction for presbyopia. Bifocal means two points of focus: the main part of the spectacle lens contains a prescription for distance vision, while the lower portion of the lens holds the stronger near prescription for close work. Some patients have difficulty accomendating to the bifocal lens and find it easier to wear one pair of glasses for distance while keeping a pair of readers available for reading and close up task. The most common complaint with glasses is they will fog up with a tempature change such as leaving a building or car to go outside. It is often difficult to keep up with a pair of reading glasses since they are taken off often.
Presbyopes also can opt for multifocal contact lenses, available in gas permeableor soft lens materials. The level with these lenses is fair, but often patients do not find the results they expected from these lenses. There are monofocal contact lenses available but again in many cases the patient will have problems adapting to the vision correction being different since one eye is for distance and the other for close up vision. The brain must learn to favor one eye or the other for different tasks. Some loss of depth perception with monovision.
Because the human lens continues to change as you grow older, your presbyopic prescription will need to be increased over time as well. You can expect your eye care practitioner to prescribe a stronger correction for near work as you need it.
Presbyopia Treatment: Surgery
Surgical options to treat presbyopia also are available. One example is Refractec Inc.'s conductive keratoplasty or NearVision CK treatment, which uses radio waves to create more curvature in the cornea for a higher "plus" prescription to improve near vision. The procedure is performed on one eye only for a monovision correction. Studies have shown that NearVision CK effectively treats presbyopia, but the correction is temporary and diminishes over time.
PresbyLASIK is a new presbyopia-correcting surgery now undergoing U.S. clinical trials. This innovative procedure uses an excimer laser to create a multifocal ablation directly on the eye's clear surface or cornea. This enables vision at multiple distances.
LASIK also can be used to create monovision, in which one eye is corrected for near vision while the other eye is stronger for distance vision.
A highly experimental treatment being studied is the injection of an elastic gel into the capsular bag, the structure in the eye that contains the natural lens. In theory, the gel would replace the natural lens and serve as a new, more elastic lens.
Experiments also have centered on laser treatment of the eye's hardened lens to increase its flexibility and thereby improve focus.
With the recent introduction of presbyopia-correcting intraocular lenses, some people undergoing cataract surgery may be able to achieve clear vision at all distances.
Also, an elective procedure known as refractive lens exchangemay enable you to replace your eye's clear but inflexible natural lens with an artificial presbyopia-correcting lens for multifocal vision.
