The Eyes (human anatomy)

 STRUCTURE OF HUMAN EYE 

The eyes: Our paired eyes arelocated in the sockets of the skulls called orbits. Each eye roughly 7 grams.   

The human eyes operate on the same basic principles as camera. A single lens focus light from all parts of the visual field onto a sheet of light sensitive cells. The region of the environment from which I collect light rays is called visual field. this sheet of light sensitive cell is called the retina.

The adult human eyeball is roughly a spherical structure. The wall of eyeball is composed of three concentric layers. The external layer of eyes is called sclera or fibrous tunic, middle layer also called uvea or vascular tunic and third layer of eyeball is called retina.

SCLERA

Sclera is composed of a dense connective tissue and that is why it is a tough layer. It is milky white in colour except in the front. Hence it form the cornea which is transparent. Cornea is a dome shaped structure. The curved surface of the cornea at refracting surface.

Therefore, cornea admits the light rays into the interior of the eyes and Bend the light ray so that they can be brought to a focus. The surface of the cornea is kept moist and dust free by the secretion from tear gland.

CHOROID

The middle court of the eyeball the choroid cote, is deeply pigmented with melanin and well supplied with the blood vessels. Choroid look blue in colour. It is not visible from outside because it covered with the sclera. The rule of choroid layer is to prevent the reflection of light rays within the eyes. This is the same function accomplished by dull black paint within the camera.

RETINA

The inner court of the eyeball is the retina. It contains the actual light receptor, the rods and cones, and thus retina function in the same way as the film of camera does. Retina contain three layers of cell form inside to outside. There are two type of photoreceptor cells namely rod and cones. These cells contain the light sensitive protein call photopigments.

RODS

There are approximately hundred million rod in each eye. Rods are used used chiefly for vision in dim light that is why tubelight vision is function of the rods. For the light to be absorbed, they must be a light absorbing substance a pigment. This light absorbing pigment is called photopigment. The rods contain a purplish red protein called the rhodopsin or visual purple. 

CONES

Unlike the rods, the cones operate only in bright light. Furthermore, they enable us to see colours. Hence, the daylight vision and colour vision a function of cones. In human eye, there are three types of cone which possess their own characteristic photopigments that respond to red, green and blue lights. The photopigment of cones are called cone pigment.

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