Human Vision (Visual Organ)

     Visual organs are used to see is the eye. Eye is the most advanced camera in the world. Connected with the eye of the occipital lobe of the brain cortex. The stimulus of the visual organ of vision or we are in the form of light. Here is the anatomy of the human eye

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            Light entering our visual system through a structure that is very complex and vulnerable. Note the msg above carefully. Cornea protect and deflect the incoming light into the lens, located behind it. If we think on the camera lenses, camera lenses work by focusing the incoming light by moving toward or away from the camera hole. The lens works by slightly altering its shape, becoming more concave or more convex to focus the light from objects near or far. The amount of light entering the eye is governed by the muscles of the iris, the part that gives the eye color. Iris surrounds a circular or slit pupils. When we're in a dark room the pupil becomes enlarged to the width or more possible  light entry. When we are on bright, sunlight for example, then the pupil will shrink or contract to limit the amount of incoming light. Visual receptors located on the back of the eye or retina (also contains specialized cells that communicate information to know the light and dark in parts of the brain to regulate biological rhythms). In the developing embryo, the retina develops from tissue removed from the brain, rather than the network that should form part of the other eye. That is to say the retina is an extension of the brain. When the eye's lens focuses light on the retina, the result is an inverted image. The light from the upper area of ​​the visual receptor cells stimulates light-sensitive retina at the bottom, and vice versa. If stimulation of the brain then interpret this upside-down as something that is not contrary. See the image below:

           Approximately 120 to 125 million receptors in the retina-shaped long, flat-called stem cells (rod). While there are 7 to 8 million funnel-shaped receptors called cone cells (cones). The most widely available receptors are also called retinal fovea. While the blind spot or blind spot is a place out of these receptors. Stem cells, more sensitive to light than cone cells. Stem cells allows us to see in the dark and at night. (Bats are able to see at night because it has very many stem cells). Stem cells to meet the outer retina, also handles peripheral vision. However, stem cells can not distinguish the various wavelengths of light so that the stem cells are not sensitive to color. While the cone cells are very sensitive and able to distinguish different wavelengths as compared with stem cells, more light to work compared with stem cells, so the cone cells need more light to work compared with stem cells.

Visual Perception Disorders
    Disorders of visual perception can occur because of brain damage in oksipitalis lobe, particularly the vision area association of such defects include: Aperseptif visual agnosia, with symptoms: - · Achromatopsia, it is  inability to distinguish colors, so to see the world as if the color gray. - · Prosopagnosia, it is : inability to recognize faces although sharp vision is normal. (Damage in the fusiform gyrus) Associative visual agnosia is the inability to recognize object although its sharp vision is normal. Thus the importance of understanding the anatomy eye for students or professionals and their study eye disorders.