Focus of the lenses
Lenses can be divided into two large groups: those designed for non-presbyopic and presbyopic people. Presbyopia or tired vision occurs after about forty years. It consists in the manifest difficulty of focusing objects, texts that are at the usual reading distance.
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In the manufacture of lenses, there are two great technologies. The conventional and the free-form. The fast improvements achieved in recent years have been achieved thanks to the development of free-form technology: each point of the lens is cut according to the mathematical calculations that give a better view without distortion. There are no previous limitations that only the surface could be cut with conventional spherical cutting tools.
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Non-presbyopic lenses:
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a) Monofocals: they are the lenses to compensate myopia, farsightedness or astigmatism. They serve both to look in close proximity as far away.
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b) Free-form monofocals adapted to digital life: the normal reading distance for an adult is about forty centimeters. It has been proven that when we look at the cell phone we place it closer, producing additional tiredness. In intensive users of the monitor or tablet, the visual system is subject to great demand. It has been proven that most people experience discomfort when they look at screens for many hours.
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Manufacturers have introduced lenses with a small addition of +0.4, +0.6 and +0.85 to the bottom of the lens to reduce fatigue and discomfort. The result is more comfort and more concentration.
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Presbyopic lenses:
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a) Monofocals: they are the same lenses that were in the previous section, with the difference that they apply to presbyopic people. These ones experience a clear vision in close vision, but not in a very close or intermediate distance. For example, a medium or advanced presbyopic may read a very clear text at 40 cm, but see the computer screen blur and, of course, the room where it is located.
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b) Progressive: they are the solution to having a clear vision in the near, middle and far. They adapt perfectly to the way people look. Adaptation to most users is very fast.
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From conventional geometry, it has evolutioned to free-form design on one side and then on two sides. Also, lenses can be optimized according to the physiological parameters (inclination of the vertical and horizontal frame, distance between the lens and the eye, rotation center, nasopupillary distances, work distance) and behavior parameters (relationship between rotation eye / turn head, lifestyle).
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c) Occupational: There are people who, when they have to work all day with a computer, looking with some progressive lenses find little visual field on the screen. From this necessity, this type of lens was born. They have a very wide field of vision and, therefore, very comfortable. There are three types: those that focus closely up to 1 meter, up to 2 meters and up to 4 meters. They are free-form designs.
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d) Bifocals: they are lenses with the part of the top to look in distant vision and a segment of near vision, down, that is visible. Currently, they adapt very little.
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