1. By the end of this, you should know:
All the parts of the eye
How vision works
What causes color blindness
What causes near- and far-sightedness

2. Vision Needs to be Developed
An infant’s eyes are sensitive to light, but there are many visual skills that must be learned in the first year of life.
What have you noticed when you have watched a baby looking at things?

3. How many directions can you move your eyes in?
Eye Movement
Each of your eyeballs is about an inch in diameter.
Your eyes are surrounded by protective tissue. The muscles around your eyes are capable of some of the fastest movements in your body.
How many directions can you move your eyes in?

4. Layers of the Eye The round walls of your eyes have three layers
The sclera
The retina
A middle layer that provides a rich blood supply
Sclera
Retina

5. Cornea
Light enters the eye through the cornea, a clear “window” in the sclera
The cornea can heal itself very fast, in just a day or two, even though it has no blood supply.
Cornea

6. How is the iris like the shutter of a camera?
Pupil and Iris
The amount of light entering the eye is monitored by the iris. The iris is made of involuntary muscles that adjust the size of the pupil based on how much light is coming in.
Pupil
Iris
How is the iris like the shutter of a camera?

7. The Lens The lens focuses light entering the eye on the retina.
The lens and the structures anterior to it are bathed a nutrient-rich fluid called aqueous humor.
Lens

8. Photoreceptors
Posterior area of eye
The retina contains photoreceptor cells called rods and cones.
Rods see dim light, gray tones, and motion.
There are three types of cones, each sensitive to a different range of color.
Rod
Cone
Interneuron

9. Photoreceptors Rods and cones adjust to changing light conditions
In a dark room, your rods take over your vision. When you come back into the light, things look very bright because your rods need to adjust to the new level of light.

10. Fovea: The Blind Spot
We have photoreceptors over our entire retina except in our blind spot
The blind spot is where the optic nerve leaves the eyeball, carrying signals to the occipital lobe.
Photoreceptors send signals to the brain through the optic nerve.
Blind spot
Optic nerve

11. Focusing Images
When light passes through the lens, it is bent by the lens and focused on the retina.
The exact point of focus is just beyond where all the incoming lines meet and cross. Because the light rays cross, the image they make on your retina is upside down.

12. Vision Problems
In nearsighted eyes, the point of focus falls in a spot in front of the retina
For farsighted people, the problem is the opposite― the focus is past the retina.

13. Vision Problems
Eyeglasses can adjust how the light is bent when it enters your eyes.
Lenses of different shapes will bend the light to different degrees so the point of focus falls on the retina.