1. Parts of the Eye - Pupil

2. Pupil
The adjustable opening in the center of the eye that controls the amount of light entering the eye (surrounded by the iris)
In bright conditions the iris expands, making the pupil smaller.
In dark conditions the iris contracts, making the pupil larger.

3. Parts of the Eye - Lens

4. Lens
A transparent structure behind the pupil; focuses the image on the back of the eye (retina)
Muscles that change the thickness of the lens change how the light is bent thereby focusing the image (Accommodation)
Glasses or contacts correct problems in the lens’ ability to focus.

5. The lens correctly focuses the image onto the back of the eye (retina).

6. (Myopia)
Misshapen eye focuses light rays from a distant object in front of the retina. Can see near but not far.

7. (Myopia)
Misshapen eye focuses light rays from near objects past the retina. Can see far but not near.
(Hyperopia)

8. Farsightedness
Nearsightedness
Astigmatism
Presbyopia

9. Parts of the Eye - Retina

10. Retina
Light-sensitive surface with cells that convert light energy to nerve impulses
At the back of the eyeball
Made up of three layers of cells
Receptor cells (Rods & Cones)
Bipolar cells
Ganglion cells

11. Parts of the Eye - Fovea

12. Fovea The central focal point of the retina
The spot where vision is best (most detailed)

13. Receptor Cells (Rods & Cones)
These cells are present in every sensory system to change (transduce) some other form of energy into neural impulses.
In sight they change light into neural impulses the brain can understand.
Visual system has two types of receptor cells – rods and cones

14. Rods Visual receptor cells located in the retina
Can only detect black and white
Respond to less light than do cones
Located around the fovea.

15. Cones Visual receptor cells located in the retina
Can detect sharp images and color
Need more light than the rods
Many cones are clustered in the fovea at the center of the retina.

16. Rods
Cones
Discovering PSY p 88 Photo at top of page

17. Distribution of Rods and Cones
Cones—concentrated in center of eye (fovea)
approx. 6 million
Rods—concentrated in periphery
approx. 120 million
Stare at a word and you’ll notice the others around it become blurred. (Clear word seen with cones, blurry area seen with Rods)
Blind spot—region with no rods or cones

18. Parts of the Eye – Optic Nerve

19. Optic Nerve
The nerve that carries visual information from the eye to the thalamus then on to the occipital lobes of the brain

20. Parts of the Eye – Blind Spot

21. Blind Spot
The point at which the optic nerve travels through the retina to exit the eye (Optic Disk)
There are no rods and cones at this point, so there is a small blind spot in vision. (do demo on page 98)
We don’t notice our blind spot because each eye compensates for the other or your brain “fills in” the missing background info. (Top-down process & Gestalt Theory)
Cover your right eye and stare at the can as you move closer to the screen. Notice the spider disappear in your peripheral vision?

22. Visual Pathway From the eye to the brain
Light travels through…
Cornea – Pupil – Lens – Fovea (retina) – Rods/Cones – Bipolar Cells – Ganglion cells (movement & light /color & detail) – Optic Nerve (blind spot) – Optic Chiasm (crossover point) – Thalamus – Occipital Lobe (Primary Visual Cortex)

23. How Can I Possibly Remember All of That in Order?
Cool = Cornea
People = Pupil
Like = Lens
Frosties = Fovea (Rods & Cones)
Because = Bipolar Cells
Gangsters = Ganglion Cells
Never = Optic Nerve
Cheat = Optic Chiasm
The = Thalamus
Officers = Occipital Lobe
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