1. The Retina

2. Eye Rap

3. The Retina
The structures of the eye are dedicated to focusing an image on the retina.
The retina is the curved screen on the back of the eye where light energy changes to electric impulses.
These electric impulses travel to the brain to be processed.

5. How the Eye Works Video

6. Nerves
When light reaches the retina, it passes through two layers of nerve cells called neurons.
After passing the neurons, the light hits a dense layer of photoreceptors.
Photoreceptors are the specialized light-sensitive neurons that that convert light energy to electric impulses.

7. Photoreceptors There are two types of photoreceptors. Cones Rods
Triangular in shape.
Respond to bright light
Distinguish color and detect fine details in objects.
Three types of cones- each respond to a different color (red, green, and blue)
Rods
Long and skinny.
Sensitive to dim light and not sensitive to bright light.
Rods cannot detect color.

8. Parts of the Retina Macula- Cone cells are concentrated here
Optic Disk
Blood Vessels
Fovea

9. Optic Disk
Optic disk- the spot where the optic nerve attaches to the back of the eye.
Has no photoreceptors at all.
Therefore, it is the blind spot in the vision of each eye.
Several large blood vessels radiate from the optic disk.

10. Blood Vessels in the Eye
Blood vessels- nourish the living tissue in the retina
Block light from reaching the photoreceptors beneath them, creating additional blind spots.

12. Fovea November 2, 2010
Fovea- A small depression in the center of the macula that contains only cone cells.
The fovea is the area of the retina that has the most sensitivity to color and detail.
This contains only cone cells.
The fovea is where an image is focused TO when you look directly at the object.

14. Field of Vision November 2, 2010
What you can see with both eyes open is your field of vision.
Typically, this is 180 degrees from side to side.
Up and down, your field of vision is about 120 degrees.
You cannot see as much up and down because of the eyebrow ridge and cheekbones--- they reduce the vertical field of vision.

15. Field of Vision: part 2 November 2, 2010
Color vision is seen in a visual field of up to 120o for bright colors, and down to 90o for pale colors
Fine detail such as that required for reading, can be seen is a narrow field of vision of about 10o

16. Reading Vision
Color Vision
Color Vision
Peripheral Vision
Peripheral Vision
Rods Only
Rods Only
Rods with some Cones
Rods with some Cones
Mostly cones

18. Blind Spots November 3, 2010
Blind spots occur where blood vessels and the optic disk block light from reaching the photoreceptors.
Blind spots are not easily detected because both eyes work together and compensate for blind spots.
In addition to the eyes working together, the brain fills in missing details, making blind spots harder to detect.

20. Peripheral vision November 3, 2010
Vision to the sides and top/bottom of our visual field.
Provides us mostly with contrast and motion information.

22. Overstimulation of Photoreceptors November 3, 2010
Rods: Saturation: when the rods get too much light, they lapse into inactivity.
Cones respond to intense light. If overstimulated, the cells in the macula and fovea can be destroyed.
This can happen if you look directly at the sun or by looking at arc welding.