The human eye is an organ which reacts to light for several purposes.
The eye is not properly a sphere, rather it is a fused two-piece unit. The smaller, less curved unit called the cornea, is linked to the larger unit called the sclera.
The cornea and sclera are connected by a ring called the limbus. The iris and its black center, the pupil, are seen instead of the cornea due to the cornea's transparency.
Dimensions differ among adults by only one or two millimeters. The vertical measure, generally less than the horizontal distance, is about 24 mm among adults, at birth about 16-17 mm. The eyeball grows rapidly, increasing to 22.5-23 mm (approx. 0.89 in) by the age of three years. From then to age 13, the eye attains its full size. The volume is 6.5 ml (0.4 cu. in.) and the weight is 7.5 g. (0.25 oz.)
The eye is made up of three coats, enclosing three transparent structures. The outermost layer is composed of the cornea and sclera. The middle layer consists of the choroid, ciliary body, and iris. The innermost is the retina, which gets its circulation from the vessels of the choroid as well as the retinal vessels, which can be seen in an opthalmoscope.
Within these coats are the aqueous humor, the vitreous body, and the flexible lens.
The aqueous humor is a clear fluid that is contained in two areas: the anterior chamber between the cornea and the iris and exposed area of the lens; and the posterior chamber, behind the iris and the rest. The lens is suspended to the ciliary body by the suspensory ligament (Zonule of Zinn), made up of fine transparent fibers. The vitreous body is a clear jelly that is much larger than the aqueous humor, and is bordered by the sclera, zonule, and lens.
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There are six Orbital Muscles
Four of the muscles control the movement of the eye going up and down and side to side.Two of the muscles control the eye to move while the head moves. For instance look in the mirror sometime, you can see your eyes looking right at it.Then stare at the mirror while moving your head side to side. You can see your eyes move but you still are looking at the mirror. That is what the other two muscles do
Muscle
Innervation
Primary function
Secondary function
Tertiary function
Levator palpebrae superioris
Oculomotor nerve
Elevation of the superior (upper) eyelid
.
.
Superior rectus
Oculomotor nerve
Elevation
Intorsion
Adduction
Inferior rectus
Oculomotor nerve
Depression
Extorsion
Adduction
Lateral rectus
Abducens nerve
Abduction
.
.
Medial rectus
Oculomotor nerve
Adduction
.
.
Superior oblique
Trochlear nerve
Intorsion
Depression
Abduction
Inferior oblique
Oculomotor nerve
Extorsion
Elevation
Abduction
This faithful reproduction of a lithograph plate fromGray's Anatomy, a two-dimensional work of art, is not copyrightable in the U.S. as per Bridgeman Art Library v. Corel Corp.; the same is also true in many other countries, including Germany. Unless stated otherwise, it is from the 20th U.S. edition of Gray's Anatomy of the Human Body, originally published in 1918 and therefore lapsed into the public domain. Other copies of Gray's Anatomy can be found on Bartleby and also on Yahoo