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

involved?involved?

About the EyeAbout the Eye The human eye is the The human eye is the

organ which gives us the organ which gives us the sense of sight, allowing sense of sight, allowing us to observe and learn us to observe and learn more about the more about the surrounding world.surrounding world.

The eye allows us to see The eye allows us to see and interpret the shapes, and interpret the shapes, colors, and dimensions of colors, and dimensions of objects in the world by objects in the world by processing the light they processing the light they reflect or emit.  reflect or emit. 

Parts of the EyeParts of the Eye The The corneacornea is the clear is the clear

dome at the front of the dome at the front of the eye, and it is perfecting eye, and it is perfecting curved, as to reduce curved, as to reduce distortion or weakening of distortion or weakening of the image passing the image passing through it.through it.

The The pupilpupil is located in the is located in the middle of the iris, and it middle of the iris, and it regulates the amount of regulates the amount of light passing through to light passing through to the retina.the retina.

The The irisiris is a thin diaphragm is a thin diaphragm composed mostly of composed mostly of connective tissue and smooth connective tissue and smooth muscle fibers; composed of muscle fibers; composed of three layers, the endothelium, three layers, the endothelium, the stroma, and the epithelium.the stroma, and the epithelium.

The color of the iris is The color of the iris is determined by the amount of determined by the amount of pigment present in the iris pigment present in the iris structure, either melanin or structure, either melanin or lipochrome.lipochrome.

   

Parts of the Eye.. Cont’dParts of the Eye.. Cont’d The transparent The transparent

crystalline lenscrystalline lens of the of the eye is located eye is located immediately behind immediately behind the iris. the iris.

When the lens When the lens becomes flat, or less becomes flat, or less convex, it enables the convex, it enables the eye to focus light from eye to focus light from far- away objects.far- away objects.

When both front and When both front and back lens surfaces back lens surfaces become more convex, become more convex, it enables the eye to it enables the eye to focus at near.focus at near.

Adjustments in lens Adjustments in lens shape, to focus at shape, to focus at various distances, is various distances, is referred to as referred to as “accommodations”. “accommodations”.

Parts of the Eye.. Cont’dParts of the Eye.. Cont’d The The sclerasclera is the tough, is the tough,

cellular tunic composed cellular tunic composed of bands of fibrous tissue, of bands of fibrous tissue, which serves to maintain which serves to maintain the shape of the eyeball.the shape of the eyeball.

The The vitreous humorvitreous humor is a is a clear gel which occupies clear gel which occupies the part of the eye the part of the eye between the crystalline between the crystalline lens and retina the and lens and retina the and occupies about 80% of occupies about 80% of the volume of the eyeball. the volume of the eyeball.

The Retina & Optic NerveThe Retina & Optic Nerve The The retina retina is the is the

innermost layer of the innermost layer of the eyeeye; ; it composed of it composed of which senses the light which senses the light entering the eye.entering the eye.

Located in the middle of Located in the middle of the retina is the the retina is the maculamacula, , which is where the which is where the highest concentration of highest concentration of cones in the are located.cones in the are located.

In the middle of the In the middle of the macula, is another macula, is another structure called the structure called the foveafovea and it is largely and it is largely responsible for color responsible for color vision in humans since it vision in humans since it contains only cones and contains only cones and no rods.no rods.

Retina LayersRetina Layers

The Retina & Optic Nerve.. The Retina & Optic Nerve.. Cont’dCont’d

The retina’s complex The retina’s complex system of nerves system of nerves then send impulses then send impulses through the through the optic optic nervenerve back to the back to the brain. brain.

The optic nerve The optic nerve transmits visual transmits visual information from the information from the retina to the brain.retina to the brain.

Diagram of the EyeDiagram of the Eye

The Occipital LobeThe Occipital Lobe The occipital lobe is The occipital lobe is

the the visual processing center of the of the brain.

Located in the Located in the rearmost portion of rearmost portion of the skull, the occipital the skull, the occipital lobes are part of the lobes are part of the forebrain structure.

Parts of the Occipital LobeParts of the Occipital Lobe The occipital lobe can be divided into several The occipital lobe can be divided into several

visual areas. visual areas. The primary visual cortex: processes info about The primary visual cortex: processes info about

static and moving objects: pattern recognitionstatic and moving objects: pattern recognition The ventral stream (visual area V2 & V4): object The ventral stream (visual area V2 & V4): object

recognition and form representation; ties to the recognition and form representation; ties to the medial temporal lobe and the limbic systemmedial temporal lobe and the limbic system

The dorsal stream (visual area V3 & V5): spatial The dorsal stream (visual area V3 & V5): spatial awareness and guidance of actionsawareness and guidance of actions

Major Damage & DiseasesMajor Damage & Diseases Myopia (Nearsightedness): light from a far away Myopia (Nearsightedness): light from a far away

object focuses before it gets to the back of the object focuses before it gets to the back of the eye eye

Hyperopia (Farsightedness): light from Hyperopia (Farsightedness): light from something far away has not focused by the time something far away has not focused by the time it reaches the back of the eyeit reaches the back of the eye

Astigmatism: one or more surfaces of the Astigmatism: one or more surfaces of the cornea or lens are not spherical, like the side of cornea or lens are not spherical, like the side of a basketball but, instead, are cylindrical or toric, a basketball but, instead, are cylindrical or toric, like the side of a footballlike the side of a football

Major Damage and Diseases Major Damage and Diseases Cont’d..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 Damage to one side of the occipital lobe causes homonomus, which is loss of vision, with exactly the loss of vision, with exactly the same "field cut" in both eyes. same "field cut" in both eyes.

Disorders of the occipital lobe can cause visual Disorders of the occipital lobe can cause visual hallucinations and illusions. Visual hallucinations can be hallucinations and illusions. Visual hallucinations can be caused by lesions to the occipital region. Visual illusions caused by lesions to the occipital region. Visual illusions can take the form of objects appearing larger or smaller can take the form of objects appearing larger or smaller than they actually are, objects lacking color or objects than they actually are, objects lacking color or objects having abnormal coloring. having abnormal coloring.

The Blind SpotThe Blind SpotThe beginning of the optic nerve in the The beginning of the optic nerve in the

retina is called 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.