2.To examine the internal parts of the eye (in order) through which light passes as it travels through the eye to the brain

APPARATUS AND MATERIALS:

Preserved sheep's eyeDissecting trayScissorsTongs

Razor bladeBlunt probeMoist paper towelPetri dish

Hand lensScalpelTweezersPins

PROCEDURE:

1.Carefully observe the eye. Determine what is fat, what is muscle, and what is other tissue

2.Carefully cut the fat from around the eye using the scalpel and scissors. Identify the six different muscle groups around the eye and determine their use. Four bands run toward the back of the eye and two bands run around the eye. Determine which muscle groups are larger. Determine the use of each muscle group by comparing to the four ways you can move your own eyes which have the same muscle groups.

3.Observe the outer layer of the eye, the sclerotic coat. Determine its colour. Observe the pupil and determine its shape. Observe the iris and determine its colour. Observe the optic nerve and determine its shape, colour, and texture. Be prepared to include this information in your observations.

4.Draw a LARGE properly formatted diagram of the external features of the eye as seen from the side with the optic nerve located on the left. Three of the muscle groups should be visible from the side of the eye. Identify the following features and add appropriate labels to your diagram of the external features:

Sclerotic coatPupil Eye lashes Eye lids IrisEye brows Eye muscles

5.Carefully remove all the muscle groups using the scalpel. Wrap the eye in a moist paper towel and store as instructed. Carefully clean your dissecting equipment and store as instructed.

6.Complete the questions in the Observation section for the External Features.

1.Place the eye on its side in the dissecting tray so that the optic nerve is to your left. Use the razor blade to make a cut around the eye about 1 cm to the right of the optic nerve as indicated in the diagram. The incision should only go through the tissue layers and should not cause a change in the shape of the eye. Be careful not to cut any more than absolutely necessary so as not to disturb the inside or damage any internal features. As you make the cut a liquid may seep out.

2.Carefully remove the back part of the eye containing the optic nerve. Try not to spill the contents of the rest of the eye. Find the thin white skin of the retina attached in the area of optic nerve. If it is not stretched out across the back of the eye try stretching it carefully to determine its size.

3.Find the thin black choroid coat layer behind the retina. Determine whether the choroid coat is thinner or thicker than the sclerotic coat. Locate the blind spot on the retina immediately in front of the point where the optic nerve emerges.

4.In the larger front section of the eye find the jelly-like vitreous humour. Carefully remove it. Behind the vitreous humour locate the extension of the choroid coat that forms the iris and also locate the round opaque ball-shaped lens. Do not remove the lens yet.

5.If you can see through the lens hold the eye close to the printing on this paper and look through it. Note the orientation of the printing compared to its appearance without the lens.

6.Use a hand lens to examine the area around the lens on the inside of the eye. Locate the very small suspensory ligaments.

7.Place the eye in the dissecting tray with the cornea down. Carefully remove the lens without moving the eye. Observe its shape. Note the liquid aqueous humour found between lens and the cornea. Locate the pupil.

8.Place the lens on the dissecting tray and cut it in half. Describe the interior of the lens.

9.Turn the eye over and look through the cornea. Note any differences between its appearance now and when the eye was intact.

10.Draw a LARGE properly formatted diagram of the internal features of the eye as seen from the side with the optic nerve located on the left. Identify the following features and add appropriate labels to your diagram of the internal features:

Vitreous humourRetinaChoroid coatLens

Aqueous humourPupilIrisSclerotic coat

Optic nerveBlind spotMuscleCornea

1.a)What colour is the fat ?

b)What colour is the muscle tissue ?

c)What colour is the outer sclerotic coating of the eye ?

2.Which muscles are larger; those controlling the up/down or those controlling the left/right motions of the eye ?

1.a)How thick is the part of the eye you are cutting ?

b)How firm is this part of the eye ?

c)Can you find more than one layer as you are cutting ? If so how many layers ?

2.a)Describe the retina (size, shape, texture etc.)

b)Is the optic nerve connected to the retina ?

c)About what fraction of the inside of the eye is covered by the retina ?

3.Is the choroid coat thinner or thicker than the sclerotic coat ?

4.a)Describe the appearance and the amount of the vitreous humour.

b)Describe the appearance of the iris.

5.Assuming you were able to see through the lens what is the appearance of the printing ?

6.a)Where are the suspensory ligaments attached ?

b)How long are the suspensory ligaments ?

7.a)How is the aqueous humour different from the vitreous humor ?

b)What shape is the lens ?

c)What shape is the pupil ?

8.Describe the appearance of the inside of the lens.

9.Describe the appearance of the pupil before and after the dissection and removal of the lens.

1.a)Would you be able to move your eyes if there were no muscles attached to your eyeball ?

b)What would you have to do to see all around if you had no eye muscles ?

c)What is a possible use for the fat surrounding the eyeball ?

d)What holds the eyeball in place so it does not fall out of the socket ?

2.What is the function of the optic nerve ?

1.What part of the eye receives the light and creates the image that we see ?

2.Name the parts of the eye (in order) that light passes through to enable us to see.

3.a) Why does the pupil not appear to be black after the dissection and removal of the lens ?

b)Why did the pupil look black before the dissection ?

4.The liquid and the jelly in the eye help the cornea and the lens to focus the light from an object on the retina. They also keep the eyeball round so that it can focus properly.

a)How would objects appear if the light coming from them were not focused properly ?

b)How can people with this problem of not being able to focus be helped ?

c)Would you be able to see if the liquid aqueous humour, the jelly-like vitreous humour and the lens were not transparent ? Explain what would happen to the light.

Answer the two questions in the original problem in a brief paragraph that clearly explains how the eye functions to enable us to see.