The Eye

Ciliary Body

Muscle attaches to ligaments

Cornea

A clear outer layer that protects the lens. This layer is made by cells on inner layer

Aqueous Humour

A clear fluid that provides nutrients and applies pressure to cornea

Pupil

A round adjustable hole in the middle of the iris

Iris

A ring of muscle around the pupil that adjusts to light conditions

Lens

An adjustable gel filled structure that focuses light on retina

Suspensory Ligaments

These are attached to the lens. They can adjust the shape of the lens

Vitreous Humour

A thick gel that provides shape and pressure to the entire eye.

Sclera

A tough white protective outer layer

Choroid

A layer of vascular tissue between the retina and Sclera. This supplies nutrients and absorbs stray light

Retina

The layer of photoreceptors

Fovea Centralis

Area of retina containing the highest density of cones. It is responsible for sharp focus

Optic Nerve

Nerve fibers that transfer photoreceptor impulses to the brain

Optic Disc (blind spot)

The area where all photoreceptor nerves leave the eye. There are no photoreceptors there

Ganglion Cells

Cells that receive sensory input from bipolar cells. Ganglion transfer impulses through the optic nerve

Bipolar Cells

A cell that extends from photoreceptors to ganglion

Rods

Photoreceptors that convert shades of light (black, greys and white) into nerve impulses

Amacrine Cells

Cells that inhibit signals arriving from bipolar cells

Horizontal Cells

Cells that inhibit signals arriving from rods and cones

Cones

Photoreceptors that convert colour (red, green and blue) into nerve impulses

Pathway of Light

1. light enters eye through a clear area of tough outer layer (sclera)

2. frontal transparent part of protective layer is cornea, helps focus images

3. light passes through an opening within a ring of muscle. this central dark opening is the pupil

4. The coloured donut shaped muscle around this opening is called the

5. Iris adjusts to varying light conditions through a process called adaptation

6. light then passes through a clear liquid filled sac (lens). This adjusts in a process called focusing. It can become flatter (further focusing) or rounder (near focusing). The change in shape is coordinated by ciliary muscle

7. Liquid in the major portion of the eyeball after lens is called vitreous humour

8. light strikes back portion of the eyes. This area is called the retina

9. image that strikes retina is reversed and inversed, brain automatically corrects for this

10. stray light within the eyeball is absorbed by a middle eyeball layer called choroid. This layer also supplied nutrients and gases

11. specialized sensors are located on retina called rods and cones

12. Rods are sensitive to varying shades of light, there are about 120 million on retina

13. cones are sensitive to red, green and blue light, there are about 6.5 million on retina

14. Receptors convert light into nerve impulses

15. impulses exit the eye through the optic nerve

16. this exit point has no light receptors, produces a blind spot

17. Directly in center portion of retina is an area with a high concentration of cones

18. fovea centralis allows for highly detailed vision, where most of incoming light is focused

Neural Interpretation of Vision

• left eye input is interpreted on right side of brain

• right eye input is interpreted on left side of brain

• use of vision from two eyes is called binocular vision