VISUAL SYSTEM The entity that sees It all

Humans have very good eyesight. Our eyes enable us to see in color as well as distinguish movement. The way this process works is light passes through the lens which shines it on the retina which is then processed by two photo receptors (rods and cones). The light is then relayed to the optic nerve which goes to the thalamus who gives the visual information to the occipital lobe of the brain’s cerebral cortex

STRUCTURE The visual system is the portion of the nervous system which allows organisms to see. The eyeball consists of the following parts: Cornea Pupil Iris Lens Retina Optic nerve

Cornea: The cornea is the clear bulging surface in front of the eye. It is the main refractive surface of the eye that covers the iris, pupil, and anterior chamber. Pupil: The pupil is the hole situated in the center of the iris of the eye that allows light to enter the retina. The iris is the layer that surrounds the pupil Iris: The iris is a thin, circular structure in the eye. It is the layer that surrounds the pupil. Lens: The lens is a transparent, bulging structure in the eye. The lens of the eye is directly behind the pupil. LOCATION AND EXPLANATION

Retina: The retina is a lining on the back inner surface of the eye that consists of photoreceptors and neurons. It consist of two photoreceptors-rods and cones-which convert light energy to electrical signals that can be interpreted by the brain. -Rods: respond best to dim light. -Cones: respond best to bright light and enable color vision. Optic Nerve: The Optic Nerve exits through the back of the eye and runs along the base of the brain to the thalamus (either of two masses of gray matter lying between the cerebral hemispheres on either side of the third ventricle).

FUNCTION The Pupil: The dark circular opening in the center of the iris of the eye, varying in size to regulate the amount of light reaching the retina The Lens: The lens is a transparent structure in the eye that, helps to refract light to be focused on the retina The Retina: The retina is a light sensitive part inside the inner layer of the eye. It has two photoreceptors: rods and cones, which receive light and transform it into image- forming signals which are transmitted through the optic nerve to the brain.

The Cornea: The most anterior structure in the eye that provides protection to the anterior chamber and acts as the outmost lens The Optic Nerve: Transfers information from the retina of the eye for analysis and integration, resulting in sight The Iris: The colored contractile membrane of the eye. It separates the anterior and posterior chambers of the eyeball and is perforated in the center by the pupil. The iris, by contraction and dilatation, regulates the entrance of light into the eye.

dISEASES Color Blindness:Color Blindness: Color blindness is caused by a difference in how light sensitive cells, in the retina, respond to certain cells, called cones, notice wave lengths of light and control the retina to recognize colors. difference in one or more cones can cause color blindness. There is no treatment but there can be adaptions.

Lazy Eye: Lazy eye may be from crossed-eyes, near-sided and far-sided, cataracts, drooping of the upper eyelid, and refractive problems. In cross- eyed case, one eye is off-focus from the object the person is trying to see. The brains nature is to ignore the off-focus image. This making the eye underused and weak. The weakened eye may become a lazy eye. The treatment is to patch the strong eye to make the weak eye stronger. You can also use contacts or glasses, surgery realigns the muscles, and if not treated soon it can become blind.

The End