Hypermétropie

From a pure optical point of view the hypermétropie is the opposite of the Myopie: the distant objects would be focused behind retina through the eye hypermétrope at rest.

" Seraient" because the luminous rays cannot obviously cross the ocular wall.
" With the repos" , i.e., without intervention of the accommodation which corresponds to a mechanism of physiological Autofocus which tends to mask, as far as possible, the hypermétropie.

The eye, always at rest, would see the all the more fuzzy objects as they approach. This definition does not give an account of lived of the hypermétrope because of accommodative faculty of the eye.

Accommodative faculty exists for two reasons.

the first is the small size of the eye to the birth and the growth prospect of the eye. All the children who will have a normal sight at the end of their ocular growth (10-12 years) were hypermétropes which were unaware of it. A certain degree of hypermétropie is thus necessary in the child: it is the physiological hypermétropie , in opposition to the hypermétropie-amétropie strictly speaking.
the second is the need for increasing the dioptric power of the eye for the vision of near. Accommodation decrease with the years to disappear completely around 55 years. This loss of the physiological autofocus is the result of the progressive reduction since the childhood of the plasticity of the cortex cristallinien and the elasticity of the capsule cristallinienne. The latter, namely the loss of the elasticity of the capsule, returns the surgery of presbyopia for a utopian substitute cristallinien.

This association reflex of the accommodation and the vision of meadows, i.e. of convergence, gives an account of the important role of the hypermétropie in convergent strabisms. In the event of hypermétropie amétropie, the hyper permanent accommodation can also involve an eyestrain and frequently appears by a pseudo early presbyopia. The hypermétropie-amétropie of the adult is generally lower than 6 dioptres. It can be of higher value, and exceed 10 dioptres. This hypermétropie strong is usually associated with other deteriorations of the eye which can be at the origin of severe complications, of acute Glaucome in particular.

Possible causes of the hypermétropie

The hypermétropie is the inadequacy of the power of the eye compared to its longueur.
Schematically one can distinguish:

the axial hypermétropie (the most frequent form) where the length of the ocular sphere is shorter for a statistically normal power. There usually exists with the birth an axial hypermétropie of 2 or 3 dioptres which decreases gradually until adolescence with the development of the eye.

the hypermétropie of power on the other hand is allotted to a too low power of the eye compared to its length, it normal. As in the case of the Myopia, the hypermétropie of power can be due either to an anomaly of the curve of an ocular diopter, or with a modification of the Index of refraction of a transparent medium of the eye.

the hypermétropie of corneal curve: in this case, the optical defect is an insufficiency of the corneal curve congenital (in extreme cases cornea planed ), or acquired (traumatism or corneal surgery for myopia).
a hypermétropie of curve cristallinienne is frequent with the age and explains the frequent hypermetropisation acquired around 55 60 years. It can also be accompanied by a peak hyperglycemic.
the hypermétropie of index is due quite simply to the absence of the crystalline lens on the optical axis (operation of the cataract, luxation of the crystalline lens) or to an artificial crystalline lens of insufficient power.

See too

Internal bonds

External bonds

Hypermétropie, explanations, vision and correction

Random links: