From a pure optical farsightedness is the opposite of myopia distant objects would be focused behind the retina through the farsighted eye to rest.
* "Would" because light rays obviously can not cross the eye wall.
* "Rest", ie without intervention of the accommodation which is a physiological autofocus mechanism that tends to hide as far as possible, hyperopia.
The eye, always at rest, see objects even more vague that they come close. This definition does not reflect the experience of farsighted because of the accommodative ability of the eye.
The possibility exists accommodative for two reasons.
* The first is the small size of the eye at birth and the prospect of growth of the eye. All children have a normal at the end of their eye growth (10-12 years) were unaware that farsighted. A degree of farsightedness is necessary in children is hyperopia physiological, as opposed to hyperopia-ametropie strict sense.
* The second is the need to increase the power diopter of the eye for near vision. The accommodation decreases over the years to completely disappear for 55 years. This loss of the Autofocus physiological is the result of the gradual decline since childhood of plasticity of the brain cristallinien and the elasticity of the capsule. This loss of elasticity of the capsule, makes surgery presbyopia for an ersatz cristallinien utopian.
This association reflex accommodation and the near vision, ie the convergence, reflects the importance of hyperopia in convergent strabismus. In case of hyperopia ametropie, hyper permanent accommodation can also cause eye strain and is frequently a pseudo early presbyopia. Farsightedness-ametropie in adults is usually less than 6 diopters. It may be higher and exceed 10 diopters. This high hyperopia is usually associated with other alterations of the eye that can cause severe complications of acute glaucoma in particular.
Possible causes of hyperopia
Farsightedness is the inadequacy of the power of the eye compared to its length.
Basically we can distinguish:
* The axial hyperopia (the most common form) where the length of the eyeball is shorter for a statistically normal power. There are usually at birth hyperopia an axial 2 or 3 diopters, which gradually decreases until adolescence with the development of the eye.
* Farsightedness power is, however, attributed to a weak power of the eye compared to its length, it normal. As in the case of myopia, hyperopia power may be due either to an abnormal curvature of a Creedmoor eye, or a change in the refractive index of a transparent medium of the eye.
o hyperopia curvature of the cornea: in this case, the default view is a lack of congenital corneal curvature (to limit cornea plana) or acquired (corneal trauma or surgery for nearsightedness).
o farsightedness cristallinienne of curvature is common with age and explains the frequent hypermetropisation gained 55 to 60 years. It may also be accompanied by a hyperglycemic peak.
o farsightedness index is simply due to the absence of the lens on the optical axis (cataract surgery, lens dislocation) or an artificial lens power insufficient.
Read also Myopia