Part I: The Eye

Part II: Sheep Eye Dissection

EYE

The eye is an extension

of the brain

It helps us take in light

information from our

surroundings.

Eye brain proximity

• Can you see :

• the optic nerve bundle?

• Spinal cord?

What are the parts of the eye?

Cornea

Cornea- transparent membrane that covers iris and pupil. Focuses light on the retina.

Pupil, Iris, Sclera

Pupil- hole passes different amounts of light

Iris- colored part of the eye that controls the size of the pupil

Sclera- “whites” of the eye that forms outer covering

Aqueous Humor, Ciliary Muscle, Lens

Aqueous Humor- nutritious fluid between the iris and the cornea. As we age, it breaks down and we begin to see “floaters”

Ciliary Muscles- produces aqueous humor and controls lens shape

Lens- Bends light rays to the back of the eye to retina.

Retina is to receive light that the lens has focused, convert the light into neural signals, and send these signals on to the brain for visual recognition.

Aqueous Humor, Ciliary Muscle, Lens

Retina

• Full of light receptors which are sensitive to:

• Cones- Colour

• Rods- Light levels

• Massive blood supply is also needed

Blind Spot- site of

optic nerve

connection

Vitreous Humor, Blind Spot, Optic Nerve,

Vitreous Humor- transparent jelly-like fluid that fills the eye and refracts light

Blind Spot- area where optic nerve attaches. No retina is located there so information cannot be picked up; “Blind”

Optic Nerve- sends messages picked up by retina to the brain

Choroid Layer, Tapetum lucidum

Choroid Layer- lies between the sclera and the retina it provides the blood supply to the eye.

Tapetum lucidum- iridescent film under the retina that provides animals with “night vision”

Cross section

You must know:1. Lens2. Cornea3. Aqueous humor4. Pupil5. Iris6. Ciliary Muscle7. Sclera8. Vitreous Humor9. Retina10. Blind Spot11. Choroid Layer12. Optic Nerve13. Tapetum Lucidum

Sclera

Blind

Spot

Ciliary

Choroid Layer

Taptem lucidum

Eye Dissection

• Before we go over the dissection, let’s review the parts of the eye and their function

TIME TO BEGIN THE SHEEP EYE DISSECTION!!!

Cut away fat using scissors

Anterior External Eye Structure

Posterior External Eye Structures

• Select a place to make an incision of the sclera midway between the cornea and optic nerve. Use the point of a surgical scissors to make a small cut through the sclera. Fluid should ooze out of the eyeball when you have cut deeply enough.

• Arrange the two hemispheres of the eye as you see in the photograph.

• Observe the semi-fluid vitreous humor that fills the central cavity of the eye. It is transparent in the living eye but might be cloudy in the preserved specimen

• The retina lines the the posterior cavity of the eye and extends forward to the ciliary body. Use your probe to lift and pull the retina back from the underlying choroid layer.

• Notice that the retina is only firmly attached to the choroid at one place. This region is the optic disc or blind spot.

Internal Eye Structure – Posterior Section

Internal Eye Structures – Anterior Section

Remove the lens and place against newspaper to see that it is a magnifier!

• When the lens is removed, an opening, allowing light to enter the eye is seen. This opening, the pupil is located in the center of the iris. Note the oblong shape of the sheep pupil, in humans the pupil is circular.

• The back side of the iris can be seen just above the pointer in the photograph.

Can you identify the parts? You will need to so you can get credit during the lab

Can you identify the parts? You will need to so you can get credit during the lab

1. Cornea

2. Sclera

3. Optic Nerve

4. Iris

5. Pupil

6. Ora Serrata (you do not have to know this structure!)

7. Ciliary Body

8. Choroid

9. Tapetum Lucidum

10. Retina

11. Lens

12. Vitreous Humor