The Eye Part 1: Structure and Function of the Eye

Eye Structure lens sclera cornea retina fovea pupil iris optic nerve

Pathway of Light Light rays pass through the clear cornea, which is then focused through the pupil.

The Pupil Dark circle in the center of the eye. The size of the pupil can be changed.. This is done by a ring of muscles called the iris, which surrounds the pupil. The color of the iris muscles vary, which defines eye color.

Dim Light Bright Light Iris muscles contract Iris muscles relax Pupil opens - dilates Pupil constricts Lets in more light Lets in less light

Iris Muscles

Pathway of Light Light passes through the lens, which further focuses the rays onto the retina.

This is done by ciliary muscles that pull the lens. A clear, flexible structure that produces an image on the eye’s retina. The lens is flexible so it can change shape, becoming thinner or thicker, depending on how far away an object is. This is done by ciliary muscles that pull the lens.

Distant Objects Near Objects Muscles contract Lens pulled thinner Focus shifts back Near Objects Muscles relax Lens made thicker Focus shifts forward

Pathway of Light The focused light rays hit a layer of light-sensitive cells found on the retina.

The Retina The retina is a layer of light sensitive cells in the back of the eye. Specialized cells called rods and cones are found deep within the retina. The retina detects images focused by the cornea and lens. Rod Cell Cone Cell

Stimulated by bright light At the edges of the retina Rods and Cones Cone Cells Center of the retina 3 types: red, green & blue Stimulated by bright light Rod Cells At the edges of the retina Light sensitive Respond to dim light

The Fovea The fovea is a dip in the center of the retina. Cone cells are concentrated in the fovea: most color vision occurs in that area Cones concentrated at the fovea

The Fovea The fovea is a dip in the center of the retina. Rods found at the edges Cones concentrated at the fovea

From Eye To Brain Your brain “sees” differently than your eye. The optic nerve from the left eye connects to the right side of the brain, and vice versa. So, your brain sees everything reversed and then switches it back.

Summary Light enters the eye through the cornea, a convex lens that focuses the light slightly. Light passes through the pupil, which is controlled by a ring of muscles called the iris. Light passes through the convex lens, which focuses the light onto the retina. The retina is a layer of light-sensitive cells: cones for color vision and rods to respond to dim light. The rods and cones send electrical impulses to the brain along the optic nerve. The optic nerve delivers the signals to the thalamus. The thalamus directs the signals to the occipital lobe where the information is processed.

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The Eye Part 2: Vision Problems and Corrections

Everyone’s vision is not perfect. This can happen in two major ways… Sight Defects Everyone’s vision is not perfect. When light doesn’t fall directly on the retina, images will appear blurry. Normal This can happen in two major ways…

Near-sightedness occurs when light is focused in front of the retina. Ability to see near, not far. Causes: Eye shape is too long Lens is too thick Fixed with a concave lens.

Near-sightedness

Far-sightedness occurs when light is focused behind the retina. Ability to see far, but not near. Causes: Eye shape is too short Lens made too thin Fixed with a convex lens.

Far-sightedness

Cataracts Cataracts cause the lens to become increasingly hard and opaque.. Cataracts are a genetic condition, which causes a person to slowly lose their vision. Blindness can result in the affected eye. Current treatment of cataracts is the surgical removal of the lens.

Cataracts

Glaucoma Blocked drainage of the aqueous humor in the eye causes glaucoma.. Pressure within the eye increase dramatically and compresses the retina and optic nerve. Common cause of blindness, and tends to occur with no obvious signs. eye fluid

Glaucoma

Any Questions?

Pre-Lab Questions What is the path of light through the eye? 2. What are rods and cones? Where are they found? 3. Describe the function of rods. 4. Describe the function of cones. 5. List the events that occur when light enters the eye.