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  • The eye

Behavior


Human eyes are two equal and symmetrical organs, positioned in the two orbital cavities of the skull.

The outer surface of each eye is a partial and opaque sphere constituted for 93% by the sclera, which IN FRONT stops giving origin to a second smaller transparent spherical portion (7% of the total area) and of different curvature, the cornea.

In the sclera there is a pigmented and vascularized layer connected to the choroid: they form the ciliary body and the iris, which is a membranous disc with a central hole (pupil) of which the diameter is adjusted by the iris muscles.

The three pigmented portions form the uveal tract or uvea. Deeply the choroid extends a photosensitive layer (retina) that ends at the junction between choroid and ciliary body.
It contains the eye photoreceptors that convert light into electrical potentials sent through the optic nerve and the visual pathway as far as the brain regions associated with the view.
The ciliary body is connected at the zonular fibers that attach to the lens to the ciliary body that changes shape through his muscles and focus.
Inside the eye there are also three rooms.

The anterior chamber is the space between the cornea and the iris, the posterior chamber is between the iris and the lens, and finally the large vitreous chamber behind the lens.
The first two are filled with ‘umore acqueo’, a clear liquid produced by the ciliary body that flows through the Schlemm's canal into scleral veins, instead of the vitreous cavity is occupied by the vitreous humor, a gelatinous mass that helps to determine the shape of the eyeball , occupying two-thirds of its volume.

Ciliary body Crystalline Anterior chamber Pupil Cornea Iris Sclera Choroid Retina Optic nerve Macula Vitreous body

Information


The eye can be compared to a camera; the lens is made from lenses that allow you to focus on the images thanks to an autofocus system.
The information is then recorded on a video cassette (Retina) and transmitted via a cable (Optic Nerve).

The eye, however, differs from the camera because the images are clearly seen only in a small area of the retina: the Macula. Normally we do not perceive this because the brain always points to the macula on the object to be recognized. The remaining part of the retina allows a less defined but wider vision. This way guarantees the fundamental visual field for orientation.

VIEW UNITS OF MEASURE:
DIOPTER Is the unit of measurement of the power of the lens shade.
Higher will be the value in diopters of a lens, more this will lessen or magnify images. The diopter should not be confused with tenths: you can see 10/10 with over 20 diopter lens. Astigmatism is expressed with an additional number that needs the direction of the lens orientation.

TENTHS
The visual acuity of the eye, also called "Visus", is the ability to distinguish the small details. Usually the normal visual acuity is expressed as a decimal. The normal value is 10/10. The tenths are measured by counting the number of rows read on special tables called "Optotypes". In case of defects of view there is a reduced visual acuity for distance and / or to close.   With the use of glasses or other techniques you can bring the visual acuity at an optimal level. Some diseases can cause reduced vision a few tenths, despite the use of glasses. In these cases a specialized control must examine the possibility of cure or rehabilitate in a timely manner the visual capabilities.