1. The Eyes

2. Internal Structures The eye is spherical.
It is made up of three tunics (walls or coats).
The Sclera
The Choroid
The Retina

3. The outermost layer of the eye is the sclera.
This fibrous, white connective tissue is known as the “white of the eye”.
The anterior portion of the sclera is a transparent window called the cornea.
The cornea allow light to enter the eye.
The sclera and the cornea have nerve endings that increase tearing when pain is detected.

4. The cornea has no blood vessels, so it can be transplanted from one person to another without fear of rejection.

6. The middle layer of the eye is the choroid
The middle layer of the eye is the choroid. Around the back of the eye, this layer is blood-rich or vascular.
The anterior portion of the choroid is made up a muscular circle. This is the colored portion of a person’s eye, or the iris.
Located in the center of the iris is a circular opening called the pupil.

7. The iris is actually made up of 2 sets of antagonistic smooth muscles:
1. sphincter
2. dilator
These involuntary muscles control the amount of light that enters the pupil.

8. Just posterior to the iris and the pupil is an elastic, protein structure called the lens.
This disk-shaped structure changes shape and allows us to focus on objects that are up close or far away.
Over time, the lens may lose its ability to change shape and then glasses become necessary.

9. The lens divides the eye cavity into 2 areas:
The interior of the eye is filled with jell-like fluids called humors that help to maintain its shape.
The lens divides the eye cavity into 2 areas:
Anterior chamber
Vitreous body
The anterior chamber is filled with aqueous humor.
The vitreous body is filled with vitreous humor.

10. L The lens is held vertically in place by suspensory ligaments.
These string-like structures extend from small muscles (part of the choroid) called the ciliary body. 1 L 2 4 6 5 3

11. The innermost layer of the eye is the retina.
The retina layer contains receptor cells called rods and cones.
Rods are sensitive to dim light.
Cones are sensitive to bright light and to colors.
Both rods and cones contribute to vision.

13. It is on the retina that light rays collect and form an image.
The image then travels via optic nerve to the occipital lobe and the result is vision.
Photoreceptor cells are found all over the retina, except where the optic nerve leaves the eye.
The lack of rods or cones equals no vision. This site is called the optic disc or the blind spot.

14. A concentration of cones also exists on the retina near the blind spot
A concentration of cones also exists on the retina near the blind spot. This area is called the fovea centralis. This is where vision is the sharpest, or most clear.
Fovea centralis

16. Pathway of Vision
Images in the light → cornea → pupil → lens → into vitreous humor (where light rays are refracted) → retina → picked up by rods and cones → optic nerve → occipital lobe of the brain where the image is interpreted.

17. Pathway of Vision

18. Anterior
Chamber
Vitreous Body