1. The Eye

2. Eye Anatomy
lens
sclera
cornea
retina
fovea
pupil
iris
optic nerve

3. Step 1
Light rays pass through the clear cornea, which focuses them through the pupil.

4. 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 gives people different eye colors.

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

6. SEM – Iris Muscles

7. Step 2
Light passes through the lens, which further focuses the rays onto the retina.

8. The thickness of the lens can be changed.
This lens can become thinner or thicker, depending on how far away an object is.
This is done by ciliary muscles that pull the lens from above and from below.

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

10. Step 3
The focused light rays hit a layer of light-sensitive cells found on the retina.

11. Rods and cones sense different things about the light that hits them.
The Retina
The retina is a layer of cells at the back of the eye that can detect light.
Specialized cells on the retina called rod and cone cells detect light.
Rods and cones sense different things about the light that hits them.
Rod Cell
Cone Cell

12. Rods and Cones Cone Cells Rod Cells At the centre of the retina
3 types: red, green & blue
Detect color
Rod Cells
At the edges of the retina
Only “see” black & white
Detect brightness

13. The Fovea The fovea is a dip in the centre of the retina.
Cone cells are concentrated in the fovea: most color vision occurs here.
Cones concentrated at the fovea

14. The Fovea The fovea is a dip in the centre of the retina.
Cone cells are concentrated in the fovea: most color vision occurs here.
Rods found at the edges
Cones concentrated at the fovea

15. 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 again!

16. Summary
Light enters the eye through the cornea, a convex lens that focuses the light slightly.
It passes through a hole called the pupil, which is controlled by a ring of muscles called the iris.
The 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 for brightness
The rods and cones send electrical impulses to the brain along the optic nerve.
The brain interprets the signals as visual images.

17. Correcting Vision

18. Sight Defects Sometimes, people’s vision is not perfect.
When light does not fall directly on the retina, images will appear blurry.
Normal
This can happen in 2 major ways…

19. Sometimes, people’s vision is not perfect.
Sight Defects
Sometimes, people’s vision is not perfect.
When light does not fall directly on the retina, images will appear blurry.
The eye shape is not perfectly spherical.
The lens muscles do not work properly.
This can happen in 2 major ways…
Short
Long
Weak
Strong

20. Nearsightedness occurs when light is focused in front of the retina.
They see well near, but not far.
Causes:
Eye shape is too long
Lens made too thick
Fixed with a concave lens.

21. Nearsightedness

22. Farsightedness occurs when light is focused behind the retina.
They see well far, but not near.
Causes:
Eye shape is too short
Lens made too thin
Fixed with a convex lens.

23. Farsightedness

24. Cataracts cause the lens to become cloudy.
Cataracts are a genetic condition that run in families, especially African Americans.
Cataracts cause a person to slowly lose their vision Blindness can result.

25. Cataracts

26. Glaucoma High pressure in the eye causes glaucoma.
Normally, fluid inside the eye is continually drained away by a drainage canal.
When this canal gets blocked, fluid builds up and pressure increases
eye fluid
This pressure pushes on the lens, affecting vision

27. Glaucoma