Eye Structure

Eye lies in eye cavity and hasoval round shape. Eye ball  and eye cavity are connected by six muscles which can generate eye movement to various direction.

Eye is composed of three layers, namely sclera, choroid, and retina.

1. Sclera is the outer layer of the eye ball in the form of tought white tissue. It maintains the shape of the eye globe. Sclera contains cornea which is transparent and composed of collagen fibers.

2. Choroid is a thin, dark tissue which lies between sclera and retina (intermediate layer), and contains a large amount of pigment and blood vessel. Between the anterior of choroid and posterior of the cornea there is iris which consists of circular muscle and contains pigment. Iris pigment determines human eye color. Iris is also important to control the amount of light entering the eyes by regulating the pupil size (a sphere located in the center of iris). When receiving strong light intensity, the pupil size will constrict. Conversely, when receiving weak light intensity, the pupil will dilate.

3. Retina is the innermost layer containing photoreceptor and nerve cells which are sensitive to light. Retina has the thickness of less than 1 milimeter. It is composed of several cell layers, which are receptor cell, ganglion cell, and nerve fibers. In the center of retina there is light focus site called yellow spot (macula lutea).