As you read this, do you wonder why you’re able to? Or what's involved?

About the Eye The human eye is the organ which gives us the sense of sight, allowing us to observe and learn more about the surrounding world. The human eye is the organ which gives us the sense of sight, allowing us to observe and learn more about the surrounding world. The eye allows us to see and interpret the shapes, colors, and dimensions of objects in the world by processing the light they reflect or emit. The eye allows us to see and interpret the shapes, colors, and dimensions of objects in the world by processing the light they reflect or emit.

Parts of the Eye The cornea is the clear dome at the front of the eye, and it is perfecting curved, as to reduce distortion or weakening of the image passing through it. The cornea is the clear dome at the front of the eye, and it is perfecting curved, as to reduce distortion or weakening of the image passing through it. The pupil is located in the middle of the iris, and it regulates the amount of light passing through to the retina. The pupil is located in the middle of the iris, and it regulates the amount of light passing through to the retina. The iris is a thin diaphragm composed mostly of connective tissue and smooth muscle fibers; composed of three layers, the endothelium, the stroma, and the epithelium. The iris is a thin diaphragm composed mostly of connective tissue and smooth muscle fibers; composed of three layers, the endothelium, the stroma, and the epithelium. The color of the iris is determined by the amount of pigment present in the iris structure, either melanin or lipochrome. The color of the iris is determined by the amount of pigment present in the iris structure, either melanin or lipochrome.

Parts of the Eye.. Cont’d The transparent crystalline lens of the eye is located immediately behind the iris. The transparent crystalline lens of the eye is located immediately behind the iris. When the lens becomes flat, or less convex, it enables the eye to focus light from far- away objects. When the lens becomes flat, or less convex, it enables the eye to focus light from far- away objects. When both front and back lens surfaces become more convex, it enables the eye to focus at near. When both front and back lens surfaces become more convex, it enables the eye to focus at near. Adjustments in lens shape, to focus at various distances, is referred to as “accommodations”. Adjustments in lens shape, to focus at various distances, is referred to as “accommodations”.

Parts of the Eye.. Cont’d The sclera is the tough, cellular tunic composed of bands of fibrous tissue, which serves to maintain the shape of the eyeball. The sclera is the tough, cellular tunic composed of bands of fibrous tissue, which serves to maintain the shape of the eyeball. The vitreous humor is a clear gel which occupies the part of the eye between the crystalline lens and retina the and occupies about 80% of the volume of the eyeball. The vitreous humor is a clear gel which occupies the part of the eye between the crystalline lens and retina the and occupies about 80% of the volume of the eyeball.

The Retina & Optic Nerve The retina is the innermost layer of the eye; it composed of which senses the light entering the eye. The retina is the innermost layer of the eye; it composed of which senses the light entering the eye. Located in the middle of the retina is the macula, which is where the highest concentration of cones in the are located. Located in the middle of the retina is the macula, which is where the highest concentration of cones in the are located. In the middle of the macula, is another structure called the fovea and it is largely responsible for color vision in humans since it contains only cones and no rods. In the middle of the macula, is another structure called the fovea and it is largely responsible for color vision in humans since it contains only cones and no rods.

Retina Layers

The Retina & Optic Nerve.. Cont’d The retina’s complex system of nerves then send impulses through the optic nerve back to the brain. The retina’s complex system of nerves then send impulses through the optic nerve back to the brain. The optic nerve transmits visual information from the retina to the brain. The optic nerve transmits visual information from the retina to the brain.

Diagram of the Eye

The Occipital Lobe The occipital lobe is the of the The occipital lobe is the visual processing center of the brain. Located in the rearmost portion of the skull, the occipital lobes are part of the Located in the rearmost portion of the skull, the occipital lobes are part of the forebrain structure.

Parts of the Occipital Lobe The occipital lobe can be divided into several visual areas. The occipital lobe can be divided into several visual areas. The primary visual cortex: processes info about static and moving objects: pattern recognition The primary visual cortex: processes info about static and moving objects: pattern recognition The ventral stream (visual area V2 & V4): object recognition and form representation; ties to the medial temporal lobe and the limbic system The ventral stream (visual area V2 & V4): object recognition and form representation; ties to the medial temporal lobe and the limbic system The dorsal stream (visual area V3 & V5): spatial awareness and guidance of actions The dorsal stream (visual area V3 & V5): spatial awareness and guidance of actions

Major Damage & Diseases Myopia (Nearsightedness): light from a far away object focuses before it gets to the back of the eye Myopia (Nearsightedness): light from a far away object focuses before it gets to the back of the eye Hyperopia (Farsightedness): light from something far away has not focused by the time it reaches the back of the eye Hyperopia (Farsightedness): light from something far away has not focused by the time it reaches the back of the eye Astigmatism: one or more surfaces of the cornea or lens are not spherical, like the side of a basketball but, instead, are cylindrical or toric, like the side of a football Astigmatism: one or more surfaces of the cornea or lens are not spherical, like the side of a basketball but, instead, are cylindrical or toric, like the side of a football

Major Damage and Diseases Cont’d.. Retinal Detachment: vitreous gel collapses, pulling on the retina causing a tear, which could lead to vitreous fluid seeping into the retina and causes its separation from the pigmented epithelium Damage to one side of the occipital lobe causes loss of vision, with exactly the same "field cut" in both eyes. Damage to one side of the occipital lobe causes homonomus, which is loss of vision, with exactly the same "field cut" in both eyes. Disorders of the occipital lobe can cause visual hallucinations and illusions. Visual hallucinations can be caused by lesions to the occipital region. Visual illusions can take the form of objects appearing larger or smaller than they actually are, objects lacking color or objects having abnormal coloring. Disorders of the occipital lobe can cause visual hallucinations and illusions. Visual hallucinations can be caused by lesions to the occipital region. Visual illusions can take the form of objects appearing larger or smaller than they actually are, objects lacking color or objects having abnormal coloring.

The Blind Spot The beginning of the optic nerve in the retina is called the The beginning of the optic nerve in the retina is called the optic nerve head or the optic disc. Since there are no photoreceptors in the optic disc, this area cannot respond to light stimulation, and one is located in each eye.