Progressive lens
Progressive Lens
A Progressive Lens (pronounced: pruh-gres-iv lenz) is a type of corrective eyewear used to correct presbyopia and other disorders of accommodation. They are also known as multifocal lenses and varifocal lenses.
Etymology
The term "progressive" in this context comes from the lens's ability to progressively adjust the optical power of the lens to provide clear vision at all distances. The term "lens" is derived from the Latin word "lens", which means "lentil", due to the similarity in shape.
Description
A Progressive Lens is characterized by a gradient of increasing lens power, added to the wearer's correction for the other refractive errors. The gradient starts at the wearer's distance prescription, at the top of the lens and reaches a maximum addition power, or the near prescription, at the bottom of the lens. The length of the progressive power gradient on the lens surface depends on the design of the lens, with a final addition power between 0.75 and 3.50 dioptres for most wearers. The addition value prescribed depends on the level of presbyopia of the patient. In general, the older the patient, the higher the addition.
Related Terms
- Presbyopia: A condition associated with the aging of the eye that results in progressively worsening ability to focus clearly on close objects.
- Refractive error: A common eye disorder that occurs when the eye cannot clearly focus the images from the outside world.
- Dioptre: The unit of measurement of the optical power of a lens or curved mirror, which is equal to the reciprocal of the focal length measured in metres.
- Accommodation (eye): The process by which the vertebrate eye changes optical power to maintain a clear image or focus on an object as its distance varies.
External links
- Medical encyclopedia article on Progressive lens
- Wikipedia's article - Progressive lens
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