Wear gloves and goggles. Place a preserved sheep eye on a dissecting tray. You will also need scissors and a dissecting needle
For each structure, indicate the tissue type
|Outer eye Structure||Function||Tissue type|
|Optic nerve||Sends impulses of vision to the brain.|
|Extrinsic eye muscles||Move eyeball up and down, right to left|
On outside of the eye to provide cushioning
Transparent covering over front of eyeball
|Sclera||The “white” of eye. Fibrous membrane surrounding posterior 5/6ths of outer eyeball|
Cut eyeball into anterior and posterior portions. Make the circular cut a few millimeters posterior to the edge of cornea. Once you have the eye in two pieces, observe the following structures. Relate each structure to its function in vision. Describe in your own words.
- Vitreous humor - gel-like substance fills posterior portion of inner eyeball. Maintains inner eyeball shape.
- Lens - clear, oval structure behind pupil. The shape of the lens changes to focus light waves onto the retina for sharp vision.
- Pupil - round opening that allows light to enter eye. The diameter of the pupil is controlled to let more, or less, light enter the eye.
- Iris - responsible for eye color. Contains muscles that control the diameter of the pupil.
- Retina - Cream-colored membrane stretched over inner back of the eyeball. Contains photoreceptors for vision. Composed of nervous tissue.
- Choroid – Absorbs excess light
* Discard eye in bucket, wash utensils and rinse the tray with water. Wash hands
Label diagram of eye - Lateral view of human eyeball. Fill in A – H.
Questions for Review
Match the structure with the function