Science Fair Project Encyclopedia
Presbyopia is a condition that occurs with growing age and results in the inability of the human eye to focus on objects up close. Presbyopia is most likely the result of a decrease in the flexibility of the lens of the eye, changes in its curvature from continual growth, and loss of power of the ciliary muscles (the muscles that bend and straighten the lens).
Presbyopia is not a disease as such, but a condition that affects everyone at a certain age. The first symptoms are usually noticed at the age of 40-50. It can start with difficulty reading fine print, particularly if the lighting is poor, or with eyestrain when reading for long periods. More advanced presbyopes may complain that their arms have become "too short" to hold reading material at a comfortable distance.
Presbyopia cannot be cured, but the loss of focusing ability can be compensated for by corrective lenses of the converging type. In subjects with other refractory problems, multifocal lenses (such as bifocal or trifocal lenses) or progressive lenses are used.
Presbyopia can be corrected with glasses or contact lenses. In some cases, the addition of bifocals to an existing lens prescription is sufficient. As the ability to focus up close worsens, the prescription needs to be changed accordingly.
Around the age of 65, the eyes have usually lost most of the elasticity needed to focus up close. However, it will still be possible to read with the help of the appropriate prescription. Even so, you may find it necessary to hold reading materials further away, and you may require larger print and more light to read by.
People who do not need glasses for distance vision may only need half glasses or reading glasses.
With the use of contact lenses, some people choose to correct one eye for near and one eye for far. This is called "monovision" and eliminates the need for bifocals or reading glasses, but can interfere with depth perception. There are also newer contact lenses that can correct for both near and far vision with the same lens.
New surgical procedures can also provide solutions for those who do not want to wear glasses or contacts.
- 1-contact-lenses-consumer-guide.com Bifocal contact lenses - simple solution for presbyopia (article)
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