What is presbyopia?
Presbyopia is not a disease in the true sense of the word, nor is it typical farsightedness. The reason for presbyopia is rather the aging process. Since this is quite natural, it is also called physiological (in contrast to “pathological” = “caused by disease”).
The physiological changes of the lens already start on the day of birth. In order to perceive objects at different distances equally well, the lens adjusts the refractive power of the eye accordingly: When it curves more, the refractive power increases so that nearby objects can be seen sharply on the retina. In the flattened state, the refractive power of the lens is lower – then distant objects can be perceived sharply. This adjustment of visual acuity by changing the shape of the lens is called accommodation.
Presbyopia: accommodation decreases
The width of accommodation indicates the range of vision in which an eye can perceive objects sharply. The lower limit is marked by the near point – the shortest distance at which someone can still perceive something sharply. The upper limit of the range of accommodation is marked by the far point – the furthest point at which someone can still see something sharply. With advancing age, the near point moves further and further into the distance – the accommodation width decreases. In ten-year-olds, for example, it is still 15 diopters, in 30-year-olds seven diopters and in 60-year-olds only one diopter.
Presbyopia: Symptoms
People with presbyopia suffer primarily because reading becomes more strenuous. They have to hold a book or newspaper with their arm further and further away from them in order to still be able to see the letters clearly. The reading distance therefore increases. Normally, it is between 30 and 40 centimeters. With presbyopia, it increases until “the arms are too short” to hold a book or newspaper far enough away for reading.
Correction of presbyopia
The following types of lenses are available for the treatment of presbyopia:
- Bifocal lenses: In these, a converging lens for near correction is cut into the lower part. The upper and middle part of the lens is a lens for distance correction.
- Trifocal lenses: Here, a third lens is ground in between the near and distance parts. This allows those affected to see sharply at medium distances, even if they have completely lost their ability to accommodate.
- Progressive lenses (progressive lenses): With these, affected individuals can see sharply at any distance without image jumps. However, the edges of the image are severely distorted.
Presbyopia in myopia
If nearsighted people become presbyopic over time, this must be taken into account when selecting the strength of the glasses: Those who are only slightly nearsighted can now remove their glasses for reading when presbyopia begins. With stronger short-sightedness the concerning needs against it either two different eyeglasses or a Gleitsichtbrille, which unites both glasses in itself, or Mehrstärken contact lenses. There are suitable glasses for working on the PC.
If farsighted people also become farsighted for age, the diopters necessary for both refractive errors must be added. Overall, the ametropia is then relatively strong. The opposite is the case with nearsighted people: Here, nearsightedness and presbyopia can even cancel each other out at close range, so that they can still manage without reading glasses for a relatively long time.
Laser treatment of presbyopia
As in the case of pathological farsightedness, it is also possible to have the eyes lasered in the case of presbyopia. However, the procedure is usually not successful in presbyopia and is therefore rarely performed.
