Synonyms in a broader sense
Hyperopia, hyperopia, hypermetropia, presbyopia, hyperopia, astigmatism, nearsightedness
Definition
In farsightedness (hyperopia) there is an imbalance between the refractive power and the length of the eyeball. Long-sighted people see well at a distance, but objects appear blurred at close range. The eyeball is too short in relation to the refractive power (axial hyperopia) or the refractive power is too weak in relation to the eyeball (refractive hyperopia).
Axial hyperopia (axial hyperopia – farsightedness) is much more common than refractive hyperopia (refractive hyperopia – farsightedness) and is almost always congenital. These are either malformations of the eyeball or the eyeball has simply grown too short. In some cases, especially in cases of severe farsightedness (hyperopia), it can also be inherited.
Refractive hyperopia is usually the so-called lentlessness, in which the eye lens is completely missing. Another cause can also be a lens dislocation (aphakic hyperopia), in which the lens is not in its natural place (lens luxation). In this case, however, the refractive power is not completely cancelled out, since it is managed by the cornea to about two thirds.
However, a person without a lens can no longer accommodate (objects in focus). In farsighted people, the focal point of rays entering the eye in parallel is imaged behind the retina. However, in order to be able to image objects in focus, the focal point must lie exactly on the retina.
With the help of the lens, a person is able to change the focus within a certain range between near and far. This process, or more precisely focusing from a distance on nearby objects, is also called accommodation. This characteristic is best developed in childhood and decreases with age due to a loss of elasticity of the lens.
This leads to the phenomenon of so-called presbyopia. Adolescents can compensate for low or medium farsightedness by their ability to accommodate by increasing their accommodation. This has two consequences: firstly, farsightedness may not be noticed until later in life and secondly, chronically increased accommodation causes the muscle responsible for accommodation (ciliary muscle) to become accustomed to it over time and not be able to relax completely (accommodation spasm).
This form of farsightedness is then also called latent hyperopia (undetected farsightedness). In adolescents, it accounts for about half of total farsightedness, and in middle age for a quarter. Only if a teenager with farsightedness makes sure that he or she wears his or her glasses contact lenses as often as possible can the ciliary muscle relax partially over time.
The other part of farsightedness, which cannot be compensated and therefore cannot be corrected by glasses or contact lenses, is called manifest hyperopia (permanent farsightedness). This is the reciprocal of the focal length. The values always refer to the far point.
This is exactly the point at which the eye is in focus without accommodating, i.e. completely relaxed. In normal vision, this point is at infinity. In the farsighted person, it is virtual and is located behind the eye.
