Since the 1990s, the number of non-prescription reading glasses purchased has surged to 30 million pairs each year. New styles, colours and features are being offered in response to customer demand. It is the magnification level, though, that makes reading glasses a functional, not just fashionable, accessory. Many people keep reading glasses in several magnification levels on hand. Inexpensive and readily available, reading glasses are finding their way into purses and glove compartments everywhere.
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Around age 40, the lens of the eye begins to stiffen, which makes it difficult to focus on closeup objects properly. This condition is called presbyopia, and it is a natural part of ageing. Holding reading material at arm's length in an effort to read it is a classic sign of presbyopia. Reading glasses with the appropriate magnification level helps people with presbyopia focus on close objects. As presbyopia progresses and the lens of the eye stiffens more, reading glasses with a greater magnification level will be needed.
Dioptre strength is the magnification level in the lenses of a pair of reading glasses. A dioptre strength of 1.00 is weak, so reading glasses have traditionally been offered with magnification levels starting at 1.50 and increasing in increments of 0.25 up to 3.00. As reading glasses have grown in popularity, the range of available magnification levels has grown as well. Reading glasses with dioptre strengths from 0.50 to 4.00 are now available. Because stress can increase presbyopia symptoms, some people keep an extra pair of reading glasses with a greater magnification level on hand.
Most people think of half glasses, like the ones Ben Franklin wore, when they think of reading glasses. Full-frame reading glasses look like traditional glasses and are best for people who spend most of their time concentrating on closeup material. Whether half or full, the magnification level is consistent throughout the entire lens in each of these reading glasses. In bifocal sunglasses, the magnification level only affects the lower portion of the lenses and the remainder of the lens is simply tinted glass.
Use an eye chart to determine the appropriate magnification level when choosing reading glasses. Simple eye charts are usually part of the display where non-prescription reading glasses are sold. Check the lenses for any bubbles, scratches or other defects. Regardless of the magnification level, reading glasses will not aid in computer viewing since the two activities differ in distance and angle of sight. Prescription reading glasses and computer glasses are available from eye-care practitioners. Since presbyopia is progressive, even the best reading glasses will probably need to be replaced with a higher magnification level every two years.
Eyes should be examined every two years even if reading glasses seem to be addressing vision problems sufficiently. Some eye diseases, such as glaucoma, have no warning symptoms but can be treated if caught early. Eye doctors can distinguish presbyopia from more serious conditions with regular eye exams. They can also provide custom reading glasses if necessary. Even good-quality non-prescription reading glasses can cause eyestrain, headaches or nausea because every human eye is different and the glasses are not. Prescription reading glasses are necessary when the patient needs custom accommodations, such as a different magnification level for each eye.
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