The structure of the eye
The eye or eyeball, is a hollow structure of generally spherical shape. It consists of tunics, a crystalline and liquid.
The outermost coat is the sclera, which is formed of a dense connective tissue and slightly vascularized, and filled and a role of protection of the eye. The front side, the sclera is replaced by the cornea, transparent. This is the cornea that allows penetration of light rays in the eyeball. It is richer in nociceptive nerve fibers: contact with an object induces the blink of the eye and lacrimal secretion (“Tears”), thereby protecting the eye contact and bacterial attacks.
Innermost these protective covers is mainly vascular tunic consists of three parts: the choroid, ciliary body and iris. The choroid is a highly vascularized membrane, pigmented brown by melanocytes. The ciliary body is mostly made up of smooth muscle through their contractions alter the shape of the lens and thus allow the accommodation The iris is the colored and visible part of the eye.; composed of smooth muscle, it can control the size of the pupil (which is its central opening) and therefore the light rays entering the eyeball: it acts as a diaphragm.
The most internal layer is the retina, composed of two layers. The pigment (outer) layer prevents light from diffusing into the eye. The inner layer is a nerve structure, composed of many photoreceptors (rods and cones) and treating cells and carrying visual information to the brain. This structure is part of the central nervous system.
Efferent nerve fibers emerging from the eye through the optic nerve, At the departure point, the retina is naturally interomptue: the blind spot (because they cannot capture any light stimulus, because of the absence of photoreceptors). Near this blind spot is the yellow spot (with a central dimple, the fovea), which is the point of the retina with the best visual acuity: this is where the light rays arrive directly with the less interference, and this is where the photoreceptor density is the most important.
The lens is a thin, elastic capsule, composed of anucleate cells and specific fibers. She plays the role of a convex lens.
The lens suspensory ligament and divide the globe into two rooms. The anterior chamber is filled with a fluid, the aqueous humor, which is continually renewed. The posterior chamber is filled with a transparent gel-like substance, the vitreous or vitreous humor. The vitreous helps in the intraocular pressure, and thus the shape of the eye.