April 26th
2009

Eye Anatomy  ⁄  Eyeball Anatomy

The normal eye is a sphere with about a 24-millimeter diameter and has three layers. The outer layer is the fibrous tunic of eyeball, the middle is the vascular tunic of eyeball, and the inner is the nervous tunic of eyeball, called the retina.

eye_anatomy

The parts of the fibrous tunic are the sclera and the cornea. The sclera is smooth and durable. The back part of the sclera is the thinnest, especially around the optic nerve. The front part of the outer layer, called the cornea, is transparent.

The parts of the vascular tunic are the iris, the ciliary body, and the choroid.


The iris is an adjustable diaphragm with an aperture in its center. The aperture, called the pupil, is narrow when subjected to bright light and wide in the dark.

The ciliary body contains an inner eye muscle, called ciliary muscle, that participates in accommodation, which is how the eye changes its focusing distance.

The choroid participates in supplyng the neuroepithelium of retina with blood.

The retina is the light-sensitive part of eye. It transforms light rays to nervous impulses, which are delivered to the brain through the optic nerve.

The macula is the area of the retina at the posterior pole of the eye responsible for fine, central vision. The oval depression in the center of the macula is called the fovea. The fovea is the most sensitive part of the retina.

From the lens to the retina, the eye is filled by the vitreous body, which contains the vitreous humor.

To obtain the best vision, the image on the retina must be clear. Therefore, the eye has a focusing system that includes the cornea and the lens, which have properties of light refraction.

The refraction unit is the diopter. For example, a one diopter lens has a one-meter focal length, a two-diopter lens has one half-meter focal length, a four-diopter lens one quarter-meter, and so on in inversely proportional dependence D=1/F.

The cornea has a refraction of about 40 diopters, and the lens has a refraction of about 20 diopters.

Take care of your eyes. Get rid of myopia the natural way.

Dr. Arkadiy Davydov.

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